[v3] cfi: fix deadloop in cfi_cmdset_0002.c do_write_buffer
diff mbox series

Message ID 1551189648-58073-1-git-send-email-liujian56@huawei.com
State Superseded
Delegated to: Vignesh R
Headers show
Series
  • [v3] cfi: fix deadloop in cfi_cmdset_0002.c do_write_buffer
Related show

Commit Message

Liu Jian Feb. 26, 2019, 2 p.m. UTC
In function do_write_buffer(), in the for loop, there is a case
chip_ready() returns 1 while chip_good() returns 0, so it never
break the loop.
To fix this, chip_good() is enough and it should timeout if it stay
bad for a while.

Fixes: dfeae1073583("mtd: cfi_cmdset_0002: Change write buffer to check correct value")
Signed-off-by: Yi Huaijie <yihuaijie@huawei.com>
Signed-off-by: Liu Jian <liujian56@huawei.com>
Reviewed-by: Tokunori Ikegami <ikegami_to@yahoo.co.jp>
---
v2->v3:
Follow Vignesh's advice:
add one more check for check_good() even when time_after() returns true.

 drivers/mtd/chips/cfi_cmdset_0002.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Tokunori Ikegami Feb. 28, 2019, 2:25 p.m. UTC | #1
> -----Original Message-----
> From: linux-mtd [mailto:linux-mtd-bounces@lists.infradead.org] On Behalf
> Of Liu Jian
> Sent: Tuesday, February 26, 2019 11:01 PM
> To: dwmw2@infradead.org; computersforpeace@gmail.com;
> bbrezillon@kernel.org; marek.vasut@gmail.com; richard@nod.at;
> joakim.tjernlund@infinera.com; ikegami@allied-telesis.co.jp;
> keescook@chromium.org; vigneshr@ti.com
> Cc: linux-mtd@lists.infradead.org; liujian56@huawei.com;
> linux-kernel@vger.kernel.org
> Subject: [PATCH v3] cfi: fix deadloop in cfi_cmdset_0002.c do_write_buffer
> 
> In function do_write_buffer(), in the for loop, there is a case
> chip_ready() returns 1 while chip_good() returns 0, so it never
> break the loop.
> To fix this, chip_good() is enough and it should timeout if it stay
> bad for a while.
> 
> Fixes: dfeae1073583("mtd: cfi_cmdset_0002: Change write buffer to check
> correct value")
> Signed-off-by: Yi Huaijie <yihuaijie@huawei.com>
> Signed-off-by: Liu Jian <liujian56@huawei.com>
> Reviewed-by: Tokunori Ikegami <ikegami_to@yahoo.co.jp>
> ---
> v2->v3:
> Follow Vignesh's advice:
> add one more check for check_good() even when time_after() returns true.
> 
>  drivers/mtd/chips/cfi_cmdset_0002.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c
> b/drivers/mtd/chips/cfi_cmdset_0002.c
> index 72428b6..3da2376 100644
> --- a/drivers/mtd/chips/cfi_cmdset_0002.c
> +++ b/drivers/mtd/chips/cfi_cmdset_0002.c
> @@ -1876,7 +1876,7 @@ static int __xipram do_write_buffer(struct map_info
> *map, struct flchip *chip,
>  			continue;
>  		}
> 
> -		if (time_after(jiffies, timeo) && !chip_ready(map, adr))
> +		if (time_after(jiffies, timeo) && !chip_good(map, adr,
> datum))

  Just another idea to understand easily.

    unsigned long now = jiffies;

    if (chip_good(map, adr, datum)) {
        xip_enable(map, chip, adr);
        goto op_done;
    }

    if (time_after(now, timeo) {
        break;
    }

Regards,
Ikegami

>  			break;
> 
>  		if (chip_good(map, adr, datum)) {
> --
> 2.7.4
> 
> 
> ______________________________________________________
> Linux MTD discussion mailing list
> http://lists.infradead.org/mailman/listinfo/linux-mtd/
Liu Jian Feb. 28, 2019, 3:12 p.m. UTC | #2
> -----Original Message-----
> From: Tokunori Ikegami [mailto:ikegami.t@gmail.com]
> Sent: Thursday, February 28, 2019 10:26 PM
> To: liujian (CE) <liujian56@huawei.com>; dwmw2@infradead.org;
> computersforpeace@gmail.com; bbrezillon@kernel.org;
> marek.vasut@gmail.com; richard@nod.at; joakim.tjernlund@infinera.com;
> ikegami@allied-telesis.co.jp; keescook@chromium.org; vigneshr@ti.com
> Cc: linux-mtd@lists.infradead.org; linux-kernel@vger.kernel.org
> Subject: RE: [PATCH v3] cfi: fix deadloop in cfi_cmdset_0002.c do_write_buffer
> 
> 
> 
> > -----Original Message-----
> > From: linux-mtd [mailto:linux-mtd-bounces@lists.infradead.org] On
> > Behalf Of Liu Jian
> > Sent: Tuesday, February 26, 2019 11:01 PM
> > To: dwmw2@infradead.org; computersforpeace@gmail.com;
> > bbrezillon@kernel.org; marek.vasut@gmail.com; richard@nod.at;
> > joakim.tjernlund@infinera.com; ikegami@allied-telesis.co.jp;
> > keescook@chromium.org; vigneshr@ti.com
> > Cc: linux-mtd@lists.infradead.org; liujian56@huawei.com;
> > linux-kernel@vger.kernel.org
> > Subject: [PATCH v3] cfi: fix deadloop in cfi_cmdset_0002.c
> > do_write_buffer
> >
> > In function do_write_buffer(), in the for loop, there is a case
> > chip_ready() returns 1 while chip_good() returns 0, so it never break
> > the loop.
> > To fix this, chip_good() is enough and it should timeout if it stay
> > bad for a while.
> >
> > Fixes: dfeae1073583("mtd: cfi_cmdset_0002: Change write buffer to
> > check correct value")
> > Signed-off-by: Yi Huaijie <yihuaijie@huawei.com>
> > Signed-off-by: Liu Jian <liujian56@huawei.com>
> > Reviewed-by: Tokunori Ikegami <ikegami_to@yahoo.co.jp>
> > ---
> > v2->v3:
> > Follow Vignesh's advice:
> > add one more check for check_good() even when time_after() returns true.
> >
> >  drivers/mtd/chips/cfi_cmdset_0002.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c
> > b/drivers/mtd/chips/cfi_cmdset_0002.c
> > index 72428b6..3da2376 100644
> > --- a/drivers/mtd/chips/cfi_cmdset_0002.c
> > +++ b/drivers/mtd/chips/cfi_cmdset_0002.c
> > @@ -1876,7 +1876,7 @@ static int __xipram do_write_buffer(struct
> > map_info *map, struct flchip *chip,
> >  			continue;
> >  		}
> >
> > -		if (time_after(jiffies, timeo) && !chip_ready(map, adr))
> > +		if (time_after(jiffies, timeo) && !chip_good(map, adr,
> > datum))
> 
>   Just another idea to understand easily.
> 
>     unsigned long now = jiffies;
> 
>     if (chip_good(map, adr, datum)) {
>         xip_enable(map, chip, adr);
>         goto op_done;
>     }
> 
>     if (time_after(now, timeo) {
>         break;
>     }
> 

Thank you~. It is more easier to understand!
If there are no other comments, I will send new patch again ):  

Best Regards,
Liujian

> Regards,
> Ikegami
> 
> >  			break;
> >
> >  		if (chip_good(map, adr, datum)) {
> > --
> > 2.7.4
> >
> >
> > ______________________________________________________
> > Linux MTD discussion mailing list
> > http://lists.infradead.org/mailman/listinfo/linux-mtd/
Boris Brezillon Feb. 28, 2019, 3:42 p.m. UTC | #3
On Thu, 28 Feb 2019 15:12:15 +0000
"liujian (CE)" <liujian56@huawei.com> wrote:

> > -----Original Message-----
> > From: Tokunori Ikegami [mailto:ikegami.t@gmail.com]
> > Sent: Thursday, February 28, 2019 10:26 PM
> > To: liujian (CE) <liujian56@huawei.com>; dwmw2@infradead.org;
> > computersforpeace@gmail.com; bbrezillon@kernel.org;
> > marek.vasut@gmail.com; richard@nod.at; joakim.tjernlund@infinera.com;
> > ikegami@allied-telesis.co.jp; keescook@chromium.org; vigneshr@ti.com
> > Cc: linux-mtd@lists.infradead.org; linux-kernel@vger.kernel.org
> > Subject: RE: [PATCH v3] cfi: fix deadloop in cfi_cmdset_0002.c do_write_buffer
> > 
> > 
> >   
> > > -----Original Message-----
> > > From: linux-mtd [mailto:linux-mtd-bounces@lists.infradead.org] On
> > > Behalf Of Liu Jian
> > > Sent: Tuesday, February 26, 2019 11:01 PM
> > > To: dwmw2@infradead.org; computersforpeace@gmail.com;
> > > bbrezillon@kernel.org; marek.vasut@gmail.com; richard@nod.at;
> > > joakim.tjernlund@infinera.com; ikegami@allied-telesis.co.jp;
> > > keescook@chromium.org; vigneshr@ti.com
> > > Cc: linux-mtd@lists.infradead.org; liujian56@huawei.com;
> > > linux-kernel@vger.kernel.org
> > > Subject: [PATCH v3] cfi: fix deadloop in cfi_cmdset_0002.c
> > > do_write_buffer
> > >
> > > In function do_write_buffer(), in the for loop, there is a case
> > > chip_ready() returns 1 while chip_good() returns 0, so it never break
> > > the loop.
> > > To fix this, chip_good() is enough and it should timeout if it stay
> > > bad for a while.
> > >
> > > Fixes: dfeae1073583("mtd: cfi_cmdset_0002: Change write buffer to
> > > check correct value")
> > > Signed-off-by: Yi Huaijie <yihuaijie@huawei.com>
> > > Signed-off-by: Liu Jian <liujian56@huawei.com>
> > > Reviewed-by: Tokunori Ikegami <ikegami_to@yahoo.co.jp>
> > > ---
> > > v2->v3:
> > > Follow Vignesh's advice:
> > > add one more check for check_good() even when time_after() returns true.
> > >
> > >  drivers/mtd/chips/cfi_cmdset_0002.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c
> > > b/drivers/mtd/chips/cfi_cmdset_0002.c
> > > index 72428b6..3da2376 100644
> > > --- a/drivers/mtd/chips/cfi_cmdset_0002.c
> > > +++ b/drivers/mtd/chips/cfi_cmdset_0002.c
> > > @@ -1876,7 +1876,7 @@ static int __xipram do_write_buffer(struct
> > > map_info *map, struct flchip *chip,
> > >  			continue;
> > >  		}
> > >
> > > -		if (time_after(jiffies, timeo) && !chip_ready(map, adr))
> > > +		if (time_after(jiffies, timeo) && !chip_good(map, adr,
> > > datum))  
> > 
> >   Just another idea to understand easily.
> > 
> >     unsigned long now = jiffies;
> > 
> >     if (chip_good(map, adr, datum)) {
> >         xip_enable(map, chip, adr);
> >         goto op_done;
> >     }
> > 
> >     if (time_after(now, timeo) {
> >         break;
> >     }
> >   
> 
> Thank you~. It is more easier to understand!
> If there are no other comments, I will send new patch again ): 

Except this version no longer does what Vignesh suggested. See how you
no longer test if chip_good() is true if time_after() returns true. So,
imagine the thread entering this function is preempted just after the
first chip_good() test, and resumed a few ms later. time_after() will
return true, but chip_good() might also return true, and you ignore it.
Tokunori Ikegami March 1, 2019, 2:51 p.m. UTC | #4
> -----Original Message-----
> From: linux-mtd [mailto:linux-mtd-bounces@lists.infradead.org] On Behalf
> Of Boris Brezillon
> Sent: Friday, March 1, 2019 12:42 AM
> To: liujian (CE)
> Cc: Tokunori Ikegami; keescook@chromium.org; bbrezillon@kernel.org;
> ikegami@allied-telesis.co.jp; richard@nod.at;
> linux-kernel@vger.kernel.org; marek.vasut@gmail.com;
> linux-mtd@lists.infradead.org; computersforpeace@gmail.com;
> dwmw2@infradead.org; vigneshr@ti.com
> Subject: Re: [PATCH v3] cfi: fix deadloop in cfi_cmdset_0002.c
> do_write_buffer
> 
> On Thu, 28 Feb 2019 15:12:15 +0000
> "liujian (CE)" <liujian56@huawei.com> wrote:
> 
> > > -----Original Message-----
> > > From: Tokunori Ikegami [mailto:ikegami.t@gmail.com]
> > > Sent: Thursday, February 28, 2019 10:26 PM
> > > To: liujian (CE) <liujian56@huawei.com>; dwmw2@infradead.org;
> > > computersforpeace@gmail.com; bbrezillon@kernel.org;
> > > marek.vasut@gmail.com; richard@nod.at;
> joakim.tjernlund@infinera.com;
> > > ikegami@allied-telesis.co.jp; keescook@chromium.org; vigneshr@ti.com
> > > Cc: linux-mtd@lists.infradead.org; linux-kernel@vger.kernel.org
> > > Subject: RE: [PATCH v3] cfi: fix deadloop in cfi_cmdset_0002.c
> do_write_buffer
> > >
> > >
> > >
> > > > -----Original Message-----
> > > > From: linux-mtd [mailto:linux-mtd-bounces@lists.infradead.org] On
> > > > Behalf Of Liu Jian
> > > > Sent: Tuesday, February 26, 2019 11:01 PM
> > > > To: dwmw2@infradead.org; computersforpeace@gmail.com;
> > > > bbrezillon@kernel.org; marek.vasut@gmail.com; richard@nod.at;
> > > > joakim.tjernlund@infinera.com; ikegami@allied-telesis.co.jp;
> > > > keescook@chromium.org; vigneshr@ti.com
> > > > Cc: linux-mtd@lists.infradead.org; liujian56@huawei.com;
> > > > linux-kernel@vger.kernel.org
> > > > Subject: [PATCH v3] cfi: fix deadloop in cfi_cmdset_0002.c
> > > > do_write_buffer
> > > >
> > > > In function do_write_buffer(), in the for loop, there is a case
> > > > chip_ready() returns 1 while chip_good() returns 0, so it never break
> > > > the loop.
> > > > To fix this, chip_good() is enough and it should timeout if it stay
> > > > bad for a while.
> > > >
> > > > Fixes: dfeae1073583("mtd: cfi_cmdset_0002: Change write buffer to
> > > > check correct value")
> > > > Signed-off-by: Yi Huaijie <yihuaijie@huawei.com>
> > > > Signed-off-by: Liu Jian <liujian56@huawei.com>
> > > > Reviewed-by: Tokunori Ikegami <ikegami_to@yahoo.co.jp>
> > > > ---
> > > > v2->v3:
> > > > Follow Vignesh's advice:
> > > > add one more check for check_good() even when time_after() returns
> true.
> > > >
> > > >  drivers/mtd/chips/cfi_cmdset_0002.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c
> > > > b/drivers/mtd/chips/cfi_cmdset_0002.c
> > > > index 72428b6..3da2376 100644
> > > > --- a/drivers/mtd/chips/cfi_cmdset_0002.c
> > > > +++ b/drivers/mtd/chips/cfi_cmdset_0002.c
> > > > @@ -1876,7 +1876,7 @@ static int __xipram do_write_buffer(struct
> > > > map_info *map, struct flchip *chip,
> > > >  			continue;
> > > >  		}
> > > >
> > > > -		if (time_after(jiffies, timeo) && !chip_ready(map, adr))
> > > > +		if (time_after(jiffies, timeo) && !chip_good(map, adr,
> > > > datum))
> > >
> > >   Just another idea to understand easily.
> > >
> > >     unsigned long now = jiffies;
> > >
> > >     if (chip_good(map, adr, datum)) {
> > >         xip_enable(map, chip, adr);
> > >         goto op_done;
> > >     }
> > >
> > >     if (time_after(now, timeo) {
> > >         break;
> > >     }
> > >
> >
> > Thank you~. It is more easier to understand!
> > If there are no other comments, I will send new patch again ):
> 
> Except this version no longer does what Vignesh suggested. See how you
> no longer test if chip_good() is true if time_after() returns true. So,
> imagine the thread entering this function is preempted just after the
> first chip_good() test, and resumed a few ms later. time_after() will
> return true, but chip_good() might also return true, and you ignore it.

I think that the following 3 versions will be worked for time_after() as a same result and follow the Vignesh-san suggestion.

1. Original Vignesh-san suggestion

	if (chip_good(map, adr, datum)) {
		xip_enable(map, chip, adr);
		goto op_done;
	}

	if (time_after(jiffies, timeo)) {
		/* Test chip_good() if TRUE incorrectly again so write failure by time_after() can be avoided. */
		if (chip_good(map, adr, datum)) {
			xip_enable(map, chip, adr);
			goto op_done;
		}
		break;
	}

2. Liujian-san v3 patch

	/* Test chip_good() if FALSE correctly so write failure by time_after() can be avoided. */
	if (time_after(jiffies, timeo) && !chip_good(map, adr))
		break;

	if (chip_good(map, adr, datum)) {
		xip_enable(map, chip, adr);
		goto op_done;
	}

3. My idea

	/* Save current jiffies value before chip_good() to avoid write failure by time_after() without testing chip_good() again. */
	unsigned long now = jiffies;

	if (chip_good(map, adr, datum)) {
		xip_enable(map, chip, adr);
		goto op_done;
	}

	if (time_after(now, timeo))
		break;

          Note: Some brackets have been fixed from the previous mail.

Regards,
Ikegami

> 
> ______________________________________________________
> Linux MTD discussion mailing list
> http://lists.infradead.org/mailman/listinfo/linux-mtd/
Boris Brezillon March 1, 2019, 4:07 p.m. UTC | #5
Hi Ikegami,

On Fri, 1 Mar 2019 23:51:16 +0900
"Tokunori Ikegami" <ikegami_to@yahoo.co.jp> wrote:

> > Except this version no longer does what Vignesh suggested. See how you
> > no longer test if chip_good() is true if time_after() returns true. So,
> > imagine the thread entering this function is preempted just after the
> > first chip_good() test, and resumed a few ms later. time_after() will
> > return true, but chip_good() might also return true, and you ignore it.  
> 
> I think that the following 3 versions will be worked for time_after() as a same result and follow the Vignesh-san suggestion.

Let me show you how they are different:

> 
> 1. Original Vignesh-san suggestion
> 
> 	if (chip_good(map, adr, datum)) {
> 		xip_enable(map, chip, adr);
> 		goto op_done;
> 	}

--> thread preempted here
==> chip_good() test becomes valid here
--> thread resumed here, but timeout has expired

> 
> 	if (time_after(jiffies, timeo)) {

you enter this branch

> 		/* Test chip_good() if TRUE incorrectly again so write failure by time_after() can be avoided. */
> 		if (chip_good(map, adr, datum)) {

chip_good() returns true

> 			xip_enable(map, chip, adr);
> 			goto op_done;
> 		}
> 		break;
> 	}
> 
> 2. Liujian-san v3 patch
> 
> 	/* Test chip_good() if FALSE correctly so write failure by time_after() can be avoided. */

--> thread preempted here
==> chip_good() test becomes valid here
--> thread resumed here, but timeout has expired

> 	if (time_after(jiffies, timeo) && !chip_good(map, adr))

You do not enter this branch because the chip_good() test is done once
more in case of timeout.

> 		break;
> 
> 	if (chip_good(map, adr, datum)) {
> 		xip_enable(map, chip, adr);
> 		goto op_done;
> 	}
> 
> 3. My idea
> 
> 	/* Save current jiffies value before chip_good() to avoid write failure by time_after() without testing chip_good() again. */
> 	unsigned long now = jiffies;
> 
> 	if (chip_good(map, adr, datum)) {
> 		xip_enable(map, chip, adr);
> 		goto op_done;
> 	}
> 

--> thread preempted here
==> chip_good() test becomes valid here
--> thread resumed here, but timeout has expired

> 	if (time_after(now, timeo))

You do enter this branch, and erroneously report a failure.

> 		break;
> 

See now why your version is not correct?

Regards,

Boris
Vignesh Raghavendra March 1, 2019, 4:47 p.m. UTC | #6
[...]
>>>>> In function do_write_buffer(), in the for loop, there is a case
>>>>> chip_ready() returns 1 while chip_good() returns 0, so it never break
>>>>> the loop.
>>>>> To fix this, chip_good() is enough and it should timeout if it stay
>>>>> bad for a while.
>>>>>
>>>>> Fixes: dfeae1073583("mtd: cfi_cmdset_0002: Change write buffer to
>>>>> check correct value")
>>>>> Signed-off-by: Yi Huaijie <yihuaijie@huawei.com>
>>>>> Signed-off-by: Liu Jian <liujian56@huawei.com>
>>>>> Reviewed-by: Tokunori Ikegami <ikegami_to@yahoo.co.jp>
>>>>> ---
>>>>> v2->v3:
>>>>> Follow Vignesh's advice:
>>>>> add one more check for check_good() even when time_after() returns
>> true.
>>>>>
>>>>>  drivers/mtd/chips/cfi_cmdset_0002.c | 2 +-
>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c
>>>>> b/drivers/mtd/chips/cfi_cmdset_0002.c
>>>>> index 72428b6..3da2376 100644
>>>>> --- a/drivers/mtd/chips/cfi_cmdset_0002.c
>>>>> +++ b/drivers/mtd/chips/cfi_cmdset_0002.c
>>>>> @@ -1876,7 +1876,7 @@ static int __xipram do_write_buffer(struct
>>>>> map_info *map, struct flchip *chip,
>>>>>  			continue;
>>>>>  		}
>>>>>
>>>>> -		if (time_after(jiffies, timeo) && !chip_ready(map, adr))
>>>>> +		if (time_after(jiffies, timeo) && !chip_good(map, adr,
>>>>> datum))
>>>>
>>>>   Just another idea to understand easily.
>>>>
>>>>     unsigned long now = jiffies;
>>>>
>>>>     if (chip_good(map, adr, datum)) {
>>>>         xip_enable(map, chip, adr);
>>>>         goto op_done;
>>>>     }
>>>>
>>>>     if (time_after(now, timeo) {
>>>>         break;
>>>>     }
>>>>
>>>
>>> Thank you~. It is more easier to understand!
>>> If there are no other comments, I will send new patch again ):
>>
>> Except this version no longer does what Vignesh suggested. See how you
>> no longer test if chip_good() is true if time_after() returns true. So,
>> imagine the thread entering this function is preempted just after the
>> first chip_good() test, and resumed a few ms later. time_after() will
>> return true, but chip_good() might also return true, and you ignore it.
> 
> I think that the following 3 versions will be worked for time_after() as a same result and follow the Vignesh-san suggestion.
> 

As Boris explained above version 3 does not really follow my
suggestion... Please see below

> 1. Original Vignesh-san suggestion
> 
> 	if (chip_good(map, adr, datum)) {
> 		xip_enable(map, chip, adr);
> 		goto op_done;
> 	}
> 
> 	if (time_after(jiffies, timeo)) {
> 		/* Test chip_good() if TRUE incorrectly again so write failure by time_after() can be avoided. */
> 		if (chip_good(map, adr, datum)) {
> 			xip_enable(map, chip, adr);
> 			goto op_done;
> 		}
> 		break;
> 	}
> 


Right, here we check chip_good() once _even when time_after() is true_
to avoid _spurious_ timeout

> 2. Liujian-san v3 patch
> 
> 	/* Test chip_good() if FALSE correctly so write failure by time_after() can be avoided. */
> 	if (time_after(jiffies, timeo) && !chip_good(map, adr))
> 		break;
> 
> 	if (chip_good(map, adr, datum)) {
> 		xip_enable(map, chip, adr);
> 		goto op_done;
> 	}
> 

This is a better version of 1

> 3. My idea
> 
> 	/* Save current jiffies value before chip_good() to avoid write failure by time_after() without testing chip_good() again. */
> 	unsigned long now = jiffies;
> 
> 	if (chip_good(map, adr, datum)) {
> 		xip_enable(map, chip, adr);
> 		goto op_done;
> 	}
> 

What if thread gets pre-empted at this point and is re-scheduled exactly
after timeo jiffies have elapsed? Below check would be true and exit loop

> 	if (time_after(now, timeo))
> 		break;
> 

So, code does not check for check chip_good() after timeoout has
elapsed. But chip_good() might be true at this point. Therefore leading
to spurious timeout.  So this version is still not right.

>           Note: Some brackets have been fixed from the previous mail.
>
Tokunori Ikegami March 1, 2019, 4:54 p.m. UTC | #7
Hi Boris-san,

> -----Original Message-----
> From: linux-mtd [mailto:linux-mtd-bounces@lists.infradead.org] On Behalf
> Of Boris Brezillon
> Sent: Saturday, March 2, 2019 1:07 AM
> To: Tokunori Ikegami
> Cc: 'Tokunori Ikegami'; keescook@chromium.org; bbrezillon@kernel.org;
> ikegami@allied-telesis.co.jp; richard@nod.at;
> linux-kernel@vger.kernel.org; marek.vasut@gmail.com;
> linux-mtd@lists.infradead.org; computersforpeace@gmail.com;
> dwmw2@infradead.org; 'liujian (CE)'; vigneshr@ti.com
> Subject: Re: [PATCH v3] cfi: fix deadloop in cfi_cmdset_0002.c
> do_write_buffer
> 
> Hi Ikegami,
> 
> On Fri, 1 Mar 2019 23:51:16 +0900
> "Tokunori Ikegami" <ikegami_to@yahoo.co.jp> wrote:
> 
> > > Except this version no longer does what Vignesh suggested. See how you
> > > no longer test if chip_good() is true if time_after() returns true.
> So,
> > > imagine the thread entering this function is preempted just after the
> > > first chip_good() test, and resumed a few ms later. time_after() will
> > > return true, but chip_good() might also return true, and you ignore
> it.
> >
> > I think that the following 3 versions will be worked for time_after()
> as a same result and follow the Vignesh-san suggestion.
> 
> Let me show you how they are different:
> 
> >
> > 1. Original Vignesh-san suggestion
> >
> > 	if (chip_good(map, adr, datum)) {
> > 		xip_enable(map, chip, adr);
> > 		goto op_done;
> > 	}
> 
> --> thread preempted here
> ==> chip_good() test becomes valid here
> --> thread resumed here, but timeout has expired
> 
> >
> > 	if (time_after(jiffies, timeo)) {
> 
> you enter this branch
> 
> > 		/* Test chip_good() if TRUE incorrectly again so write
> failure by time_after() can be avoided. */
> > 		if (chip_good(map, adr, datum)) {
> 
> chip_good() returns true
> 
> > 			xip_enable(map, chip, adr);
> > 			goto op_done;
> > 		}
> > 		break;
> > 	}
> >
> > 2. Liujian-san v3 patch
> >
> > 	/* Test chip_good() if FALSE correctly so write failure by
> time_after() can be avoided. */
> 
> --> thread preempted here
> ==> chip_good() test becomes valid here
> --> thread resumed here, but timeout has expired
> 
> > 	if (time_after(jiffies, timeo) && !chip_good(map, adr))
> 
> You do not enter this branch because the chip_good() test is done once
> more in case of timeout.
> 
> > 		break;
> >
> > 	if (chip_good(map, adr, datum)) {
> > 		xip_enable(map, chip, adr);
> > 		goto op_done;
> > 	}
> >
> > 3. My idea
> >
> > 	/* Save current jiffies value before chip_good() to avoid write
> failure by time_after() without testing chip_good() again. */
> > 	unsigned long now = jiffies;
> >
> > 	if (chip_good(map, adr, datum)) {
> > 		xip_enable(map, chip, adr);
> > 		goto op_done;
> > 	}
> >
> 
> --> thread preempted here
> ==> chip_good() test becomes valid here
> --> thread resumed here, but timeout has expired
> 
> > 	if (time_after(now, timeo))
> 
> You do enter this branch, and erroneously report a failure.

I do not think that it is not entered here since the value timeo is compare
with the saved value now before the chip_bood() by time_after().

> 
> > 		break;
> >
> 
> See now why your version is not correct?
> 
> Regards,
> 
> Boris
> 
> ______________________________________________________
> Linux MTD discussion mailing list
> http://lists.infradead.org/mailman/listinfo/linux-mtd/
Tokunori Ikegami March 1, 2019, 4:59 p.m. UTC | #8
> [...]
> >>>>> In function do_write_buffer(), in the for loop, there is a case
> >>>>> chip_ready() returns 1 while chip_good() returns 0, so it never break
> >>>>> the loop.
> >>>>> To fix this, chip_good() is enough and it should timeout if it stay
> >>>>> bad for a while.
> >>>>>
> >>>>> Fixes: dfeae1073583("mtd: cfi_cmdset_0002: Change write buffer to
> >>>>> check correct value")
> >>>>> Signed-off-by: Yi Huaijie <yihuaijie@huawei.com>
> >>>>> Signed-off-by: Liu Jian <liujian56@huawei.com>
> >>>>> Reviewed-by: Tokunori Ikegami <ikegami_to@yahoo.co.jp>
> >>>>> ---
> >>>>> v2->v3:
> >>>>> Follow Vignesh's advice:
> >>>>> add one more check for check_good() even when time_after() returns
> >> true.
> >>>>>
> >>>>>  drivers/mtd/chips/cfi_cmdset_0002.c | 2 +-
> >>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>>
> >>>>> diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c
> >>>>> b/drivers/mtd/chips/cfi_cmdset_0002.c
> >>>>> index 72428b6..3da2376 100644
> >>>>> --- a/drivers/mtd/chips/cfi_cmdset_0002.c
> >>>>> +++ b/drivers/mtd/chips/cfi_cmdset_0002.c
> >>>>> @@ -1876,7 +1876,7 @@ static int __xipram do_write_buffer(struct
> >>>>> map_info *map, struct flchip *chip,
> >>>>>  			continue;
> >>>>>  		}
> >>>>>
> >>>>> -		if (time_after(jiffies, timeo) && !chip_ready(map, adr))
> >>>>> +		if (time_after(jiffies, timeo) && !chip_good(map, adr,
> >>>>> datum))
> >>>>
> >>>>   Just another idea to understand easily.
> >>>>
> >>>>     unsigned long now = jiffies;
> >>>>
> >>>>     if (chip_good(map, adr, datum)) {
> >>>>         xip_enable(map, chip, adr);
> >>>>         goto op_done;
> >>>>     }
> >>>>
> >>>>     if (time_after(now, timeo) {
> >>>>         break;
> >>>>     }
> >>>>
> >>>
> >>> Thank you~. It is more easier to understand!
> >>> If there are no other comments, I will send new patch again ):
> >>
> >> Except this version no longer does what Vignesh suggested. See how you
> >> no longer test if chip_good() is true if time_after() returns true. So,
> >> imagine the thread entering this function is preempted just after the
> >> first chip_good() test, and resumed a few ms later. time_after() will
> >> return true, but chip_good() might also return true, and you ignore it.
> >
> > I think that the following 3 versions will be worked for time_after()
> as a same result and follow the Vignesh-san suggestion.
> >
> 
> As Boris explained above version 3 does not really follow my
> suggestion... Please see below
> 
> > 1. Original Vignesh-san suggestion
> >
> > 	if (chip_good(map, adr, datum)) {
> > 		xip_enable(map, chip, adr);
> > 		goto op_done;
> > 	}
> >
> > 	if (time_after(jiffies, timeo)) {
> > 		/* Test chip_good() if TRUE incorrectly again so write
> failure by time_after() can be avoided. */
> > 		if (chip_good(map, adr, datum)) {
> > 			xip_enable(map, chip, adr);
> > 			goto op_done;
> > 		}
> > 		break;
> > 	}
> >
> 
> 
> Right, here we check chip_good() once _even when time_after() is true_
> to avoid _spurious_ timeout
> 
> > 2. Liujian-san v3 patch
> >
> > 	/* Test chip_good() if FALSE correctly so write failure by
> time_after() can be avoided. */
> > 	if (time_after(jiffies, timeo) && !chip_good(map, adr))
> > 		break;
> >
> > 	if (chip_good(map, adr, datum)) {
> > 		xip_enable(map, chip, adr);
> > 		goto op_done;
> > 	}
> >
> 
> This is a better version of 1
> 
> > 3. My idea
> >
> > 	/* Save current jiffies value before chip_good() to avoid write
> failure by time_after() without testing chip_good() again. */
> > 	unsigned long now = jiffies;
> >
> > 	if (chip_good(map, adr, datum)) {
> > 		xip_enable(map, chip, adr);
> > 		goto op_done;
> > 	}
> >
> 
> What if thread gets pre-empted at this point and is re-scheduled exactly
> after timeo jiffies have elapsed? Below check would be true and exit loop

  I think that the jiffies value now is save before chip_good() so below check would be false and not exit loop.

Regards,
Ikegami

> 
> > 	if (time_after(now, timeo))
> > 		break;
> >
> 
> So, code does not check for check chip_good() after timeoout has
> elapsed. But chip_good() might be true at this point. Therefore leading
> to spurious timeout.  So this version is still not right.
> 
> >           Note: Some brackets have been fixed from the previous mail.
> >
> 
> ______________________________________________________
> Linux MTD discussion mailing list
> http://lists.infradead.org/mailman/listinfo/linux-mtd/
Boris Brezillon March 1, 2019, 5:43 p.m. UTC | #9
On Sat, 2 Mar 2019 01:59:41 +0900
"Tokunori Ikegami" <ikegami.t@gmail.com> wrote:

> > [...]  
> > >>>>> In function do_write_buffer(), in the for loop, there is a
> > >>>>> case chip_ready() returns 1 while chip_good() returns 0, so
> > >>>>> it never break the loop.
> > >>>>> To fix this, chip_good() is enough and it should timeout if
> > >>>>> it stay bad for a while.
> > >>>>>
> > >>>>> Fixes: dfeae1073583("mtd: cfi_cmdset_0002: Change write
> > >>>>> buffer to check correct value")
> > >>>>> Signed-off-by: Yi Huaijie <yihuaijie@huawei.com>
> > >>>>> Signed-off-by: Liu Jian <liujian56@huawei.com>
> > >>>>> Reviewed-by: Tokunori Ikegami <ikegami_to@yahoo.co.jp>
> > >>>>> ---
> > >>>>> v2->v3:
> > >>>>> Follow Vignesh's advice:
> > >>>>> add one more check for check_good() even when time_after()
> > >>>>> returns  
> > >> true.  
> > >>>>>
> > >>>>>  drivers/mtd/chips/cfi_cmdset_0002.c | 2 +-
> > >>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
> > >>>>>
> > >>>>> diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c
> > >>>>> b/drivers/mtd/chips/cfi_cmdset_0002.c
> > >>>>> index 72428b6..3da2376 100644
> > >>>>> --- a/drivers/mtd/chips/cfi_cmdset_0002.c
> > >>>>> +++ b/drivers/mtd/chips/cfi_cmdset_0002.c
> > >>>>> @@ -1876,7 +1876,7 @@ static int __xipram
> > >>>>> do_write_buffer(struct map_info *map, struct flchip *chip,
> > >>>>>  			continue;
> > >>>>>  		}
> > >>>>>
> > >>>>> -		if (time_after(jiffies, timeo)
> > >>>>> && !chip_ready(map, adr))
> > >>>>> +		if (time_after(jiffies, timeo)
> > >>>>> && !chip_good(map, adr, datum))  
> > >>>>
> > >>>>   Just another idea to understand easily.
> > >>>>
> > >>>>     unsigned long now = jiffies;
> > >>>>
> > >>>>     if (chip_good(map, adr, datum)) {
> > >>>>         xip_enable(map, chip, adr);
> > >>>>         goto op_done;
> > >>>>     }
> > >>>>
> > >>>>     if (time_after(now, timeo) {
> > >>>>         break;
> > >>>>     }
> > >>>>  
> > >>>
> > >>> Thank you~. It is more easier to understand!
> > >>> If there are no other comments, I will send new patch again ):  
> > >>
> > >> Except this version no longer does what Vignesh suggested. See
> > >> how you no longer test if chip_good() is true if time_after()
> > >> returns true. So, imagine the thread entering this function is
> > >> preempted just after the first chip_good() test, and resumed a
> > >> few ms later. time_after() will return true, but chip_good()
> > >> might also return true, and you ignore it.  
> > >
> > > I think that the following 3 versions will be worked for
> > > time_after()  
> > as a same result and follow the Vignesh-san suggestion.  
> > >  
> > 
> > As Boris explained above version 3 does not really follow my
> > suggestion... Please see below
> >   
> > > 1. Original Vignesh-san suggestion
> > >
> > > 	if (chip_good(map, adr, datum)) {
> > > 		xip_enable(map, chip, adr);
> > > 		goto op_done;
> > > 	}
> > >
> > > 	if (time_after(jiffies, timeo)) {
> > > 		/* Test chip_good() if TRUE incorrectly again so
> > > write  
> > failure by time_after() can be avoided. */  
> > > 		if (chip_good(map, adr, datum)) {
> > > 			xip_enable(map, chip, adr);
> > > 			goto op_done;
> > > 		}
> > > 		break;
> > > 	}
> > >  
> > 
> > 
> > Right, here we check chip_good() once _even when time_after() is
> > true_ to avoid _spurious_ timeout
> >   
> > > 2. Liujian-san v3 patch
> > >
> > > 	/* Test chip_good() if FALSE correctly so write failure
> > > by  
> > time_after() can be avoided. */  
> > > 	if (time_after(jiffies, timeo) && !chip_good(map, adr))
> > > 		break;
> > >
> > > 	if (chip_good(map, adr, datum)) {
> > > 		xip_enable(map, chip, adr);
> > > 		goto op_done;
> > > 	}
> > >  
> > 
> > This is a better version of 1
> >   
> > > 3. My idea
> > >
> > > 	/* Save current jiffies value before chip_good() to avoid
> > > write  
> > failure by time_after() without testing chip_good() again. */  
> > > 	unsigned long now = jiffies;
> > >
> > > 	if (chip_good(map, adr, datum)) {
> > > 		xip_enable(map, chip, adr);
> > > 		goto op_done;
> > > 	}
> > >  
> > 
> > What if thread gets pre-empted at this point and is re-scheduled
> > exactly after timeo jiffies have elapsed? Below check would be true
> > and exit loop  
> 
>   I think that the jiffies value now is save before chip_good() so
> below check would be false and not exit loop.

True, I overlooked that part, and so Vignesh did. This proves one
thing: code is not easier to follow with your version. IMO, if we want
to make things clear, we should add a comment to Liujian's explaining
why the extra test after time_after(jiffies, timeo) is needed.
Tokunori Ikegami March 1, 2019, 5:55 p.m. UTC | #10
> > > [...]
> > > >>>>> In function do_write_buffer(), in the for loop, there is a
> > > >>>>> case chip_ready() returns 1 while chip_good() returns 0, so
> > > >>>>> it never break the loop.
> > > >>>>> To fix this, chip_good() is enough and it should timeout if
> > > >>>>> it stay bad for a while.
> > > >>>>>
> > > >>>>> Fixes: dfeae1073583("mtd: cfi_cmdset_0002: Change write
> > > >>>>> buffer to check correct value")
> > > >>>>> Signed-off-by: Yi Huaijie <yihuaijie@huawei.com>
> > > >>>>> Signed-off-by: Liu Jian <liujian56@huawei.com>
> > > >>>>> Reviewed-by: Tokunori Ikegami <ikegami_to@yahoo.co.jp>
> > > >>>>> ---
> > > >>>>> v2->v3:
> > > >>>>> Follow Vignesh's advice:
> > > >>>>> add one more check for check_good() even when time_after()
> > > >>>>> returns
> > > >> true.
> > > >>>>>
> > > >>>>>  drivers/mtd/chips/cfi_cmdset_0002.c | 2 +-
> > > >>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >>>>>
> > > >>>>> diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c
> > > >>>>> b/drivers/mtd/chips/cfi_cmdset_0002.c
> > > >>>>> index 72428b6..3da2376 100644
> > > >>>>> --- a/drivers/mtd/chips/cfi_cmdset_0002.c
> > > >>>>> +++ b/drivers/mtd/chips/cfi_cmdset_0002.c
> > > >>>>> @@ -1876,7 +1876,7 @@ static int __xipram
> > > >>>>> do_write_buffer(struct map_info *map, struct flchip *chip,
> > > >>>>>  			continue;
> > > >>>>>  		}
> > > >>>>>
> > > >>>>> -		if (time_after(jiffies, timeo)
> > > >>>>> && !chip_ready(map, adr))
> > > >>>>> +		if (time_after(jiffies, timeo)
> > > >>>>> && !chip_good(map, adr, datum))
> > > >>>>
> > > >>>>   Just another idea to understand easily.
> > > >>>>
> > > >>>>     unsigned long now = jiffies;
> > > >>>>
> > > >>>>     if (chip_good(map, adr, datum)) {
> > > >>>>         xip_enable(map, chip, adr);
> > > >>>>         goto op_done;
> > > >>>>     }
> > > >>>>
> > > >>>>     if (time_after(now, timeo) {
> > > >>>>         break;
> > > >>>>     }
> > > >>>>
> > > >>>
> > > >>> Thank you~. It is more easier to understand!
> > > >>> If there are no other comments, I will send new patch again ):
> > > >>
> > > >> Except this version no longer does what Vignesh suggested. See
> > > >> how you no longer test if chip_good() is true if time_after()
> > > >> returns true. So, imagine the thread entering this function is
> > > >> preempted just after the first chip_good() test, and resumed a
> > > >> few ms later. time_after() will return true, but chip_good()
> > > >> might also return true, and you ignore it.
> > > >
> > > > I think that the following 3 versions will be worked for
> > > > time_after()
> > > as a same result and follow the Vignesh-san suggestion.
> > > >
> > >
> > > As Boris explained above version 3 does not really follow my
> > > suggestion... Please see below
> > >
> > > > 1. Original Vignesh-san suggestion
> > > >
> > > > 	if (chip_good(map, adr, datum)) {
> > > > 		xip_enable(map, chip, adr);
> > > > 		goto op_done;
> > > > 	}
> > > >
> > > > 	if (time_after(jiffies, timeo)) {
> > > > 		/* Test chip_good() if TRUE incorrectly again so
> > > > write
> > > failure by time_after() can be avoided. */
> > > > 		if (chip_good(map, adr, datum)) {
> > > > 			xip_enable(map, chip, adr);
> > > > 			goto op_done;
> > > > 		}
> > > > 		break;
> > > > 	}
> > > >
> > >
> > >
> > > Right, here we check chip_good() once _even when time_after() is
> > > true_ to avoid _spurious_ timeout
> > >
> > > > 2. Liujian-san v3 patch
> > > >
> > > > 	/* Test chip_good() if FALSE correctly so write failure
> > > > by
> > > time_after() can be avoided. */
> > > > 	if (time_after(jiffies, timeo) && !chip_good(map, adr))
> > > > 		break;
> > > >
> > > > 	if (chip_good(map, adr, datum)) {
> > > > 		xip_enable(map, chip, adr);
> > > > 		goto op_done;
> > > > 	}
> > > >
> > >
> > > This is a better version of 1
> > >
> > > > 3. My idea
> > > >
> > > > 	/* Save current jiffies value before chip_good() to avoid
> > > > write
> > > failure by time_after() without testing chip_good() again. */
> > > > 	unsigned long now = jiffies;
> > > >
> > > > 	if (chip_good(map, adr, datum)) {
> > > > 		xip_enable(map, chip, adr);
> > > > 		goto op_done;
> > > > 	}
> > > >
> > >
> > > What if thread gets pre-empted at this point and is re-scheduled
> > > exactly after timeo jiffies have elapsed? Below check would be true
> > > and exit loop
> >
> >   I think that the jiffies value now is save before chip_good() so
> > below check would be false and not exit loop.
> 
> True, I overlooked that part, and so Vignesh did. This proves one
> thing: code is not easier to follow with your version. IMO, if we want
> to make things clear, we should add a comment to Liujian's explaining
> why the extra test after time_after(jiffies, timeo) is needed.

I see so I am okay with the change of Liujian-san v3 patch.
Also agree with the comment to be added.

Regards,
Ikegami

> 
> ______________________________________________________
> Linux MTD discussion mailing list
> http://lists.infradead.org/mailman/listinfo/linux-mtd/
Boris Brezillon March 1, 2019, 7:56 p.m. UTC | #11
The "mtd: " prefix is still missing. Should be "mtd: cfi: ". If you
send a new version, please fix that.

Thanks,

Boris

On Tue, 26 Feb 2019 22:00:48 +0800
Liu Jian <liujian56@huawei.com> wrote:

> In function do_write_buffer(), in the for loop, there is a case
> chip_ready() returns 1 while chip_good() returns 0, so it never
> break the loop.
> To fix this, chip_good() is enough and it should timeout if it stay
> bad for a while.
> 
> Fixes: dfeae1073583("mtd: cfi_cmdset_0002: Change write buffer to check correct value")
> Signed-off-by: Yi Huaijie <yihuaijie@huawei.com>
> Signed-off-by: Liu Jian <liujian56@huawei.com>
> Reviewed-by: Tokunori Ikegami <ikegami_to@yahoo.co.jp>
> ---
> v2->v3:
> Follow Vignesh's advice:
> add one more check for check_good() even when time_after() returns true.
> 
>  drivers/mtd/chips/cfi_cmdset_0002.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c b/drivers/mtd/chips/cfi_cmdset_0002.c
> index 72428b6..3da2376 100644
> --- a/drivers/mtd/chips/cfi_cmdset_0002.c
> +++ b/drivers/mtd/chips/cfi_cmdset_0002.c
> @@ -1876,7 +1876,7 @@ static int __xipram do_write_buffer(struct map_info *map, struct flchip *chip,
>  			continue;
>  		}
>  
> -		if (time_after(jiffies, timeo) && !chip_ready(map, adr))
> +		if (time_after(jiffies, timeo) && !chip_good(map, adr, datum))
>  			break;
>  
>  		if (chip_good(map, adr, datum)) {
Vignesh Raghavendra March 2, 2019, 8:57 a.m. UTC | #12
On 01-Mar-19 11:25 PM, Tokunori Ikegami wrote:
>>>> [...]
>>>>>>>>> In function do_write_buffer(), in the for loop, there is a
>>>>>>>>> case chip_ready() returns 1 while chip_good() returns 0, so
>>>>>>>>> it never break the loop.
>>>>>>>>> To fix this, chip_good() is enough and it should timeout if
>>>>>>>>> it stay bad for a while.
>>>>>>>>>
>>>>>>>>> Fixes: dfeae1073583("mtd: cfi_cmdset_0002: Change write
>>>>>>>>> buffer to check correct value")
>>>>>>>>> Signed-off-by: Yi Huaijie <yihuaijie@huawei.com>
>>>>>>>>> Signed-off-by: Liu Jian <liujian56@huawei.com>
>>>>>>>>> Reviewed-by: Tokunori Ikegami <ikegami_to@yahoo.co.jp>
>>>>>>>>> ---
>>>>>>>>> v2->v3:
>>>>>>>>> Follow Vignesh's advice:
>>>>>>>>> add one more check for check_good() even when time_after()
>>>>>>>>> returns
>>>>>> true.
>>>>>>>>>
>>>>>>>>>  drivers/mtd/chips/cfi_cmdset_0002.c | 2 +-
>>>>>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>>>>
>>>>>>>>> diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c
>>>>>>>>> b/drivers/mtd/chips/cfi_cmdset_0002.c
>>>>>>>>> index 72428b6..3da2376 100644
>>>>>>>>> --- a/drivers/mtd/chips/cfi_cmdset_0002.c
>>>>>>>>> +++ b/drivers/mtd/chips/cfi_cmdset_0002.c
>>>>>>>>> @@ -1876,7 +1876,7 @@ static int __xipram
>>>>>>>>> do_write_buffer(struct map_info *map, struct flchip *chip,
>>>>>>>>>  			continue;
>>>>>>>>>  		}
>>>>>>>>>
>>>>>>>>> -		if (time_after(jiffies, timeo)
>>>>>>>>> && !chip_ready(map, adr))
>>>>>>>>> +		if (time_after(jiffies, timeo)
>>>>>>>>> && !chip_good(map, adr, datum))
>>>>>>>>
>>>>>>>>   Just another idea to understand easily.
>>>>>>>>
>>>>>>>>     unsigned long now = jiffies;
>>>>>>>>
>>>>>>>>     if (chip_good(map, adr, datum)) {
>>>>>>>>         xip_enable(map, chip, adr);
>>>>>>>>         goto op_done;
>>>>>>>>     }
>>>>>>>>
>>>>>>>>     if (time_after(now, timeo) {
>>>>>>>>         break;
>>>>>>>>     }
>>>>>>>>
>>>>>>>
>>>>>>> Thank you~. It is more easier to understand!
>>>>>>> If there are no other comments, I will send new patch again ):
>>>>>>
>>>>>> Except this version no longer does what Vignesh suggested. See
>>>>>> how you no longer test if chip_good() is true if time_after()
>>>>>> returns true. So, imagine the thread entering this function is
>>>>>> preempted just after the first chip_good() test, and resumed a
>>>>>> few ms later. time_after() will return true, but chip_good()
>>>>>> might also return true, and you ignore it.
>>>>>
>>>>> I think that the following 3 versions will be worked for
>>>>> time_after()
>>>> as a same result and follow the Vignesh-san suggestion.
>>>>>
>>>>
>>>> As Boris explained above version 3 does not really follow my
>>>> suggestion... Please see below
>>>>
>>>>> 1. Original Vignesh-san suggestion
>>>>>
>>>>> 	if (chip_good(map, adr, datum)) {
>>>>> 		xip_enable(map, chip, adr);
>>>>> 		goto op_done;
>>>>> 	}
>>>>>
>>>>> 	if (time_after(jiffies, timeo)) {
>>>>> 		/* Test chip_good() if TRUE incorrectly again so
>>>>> write
>>>> failure by time_after() can be avoided. */
>>>>> 		if (chip_good(map, adr, datum)) {
>>>>> 			xip_enable(map, chip, adr);
>>>>> 			goto op_done;
>>>>> 		}
>>>>> 		break;
>>>>> 	}
>>>>>
>>>>
>>>>
>>>> Right, here we check chip_good() once _even when time_after() is
>>>> true_ to avoid _spurious_ timeout
>>>>
>>>>> 2. Liujian-san v3 patch
>>>>>
>>>>> 	/* Test chip_good() if FALSE correctly so write failure
>>>>> by
>>>> time_after() can be avoided. */
>>>>> 	if (time_after(jiffies, timeo) && !chip_good(map, adr))
>>>>> 		break;
>>>>>
>>>>> 	if (chip_good(map, adr, datum)) {
>>>>> 		xip_enable(map, chip, adr);
>>>>> 		goto op_done;
>>>>> 	}
>>>>>
>>>>
>>>> This is a better version of 1
>>>>
>>>>> 3. My idea
>>>>>
>>>>> 	/* Save current jiffies value before chip_good() to avoid
>>>>> write
>>>> failure by time_after() without testing chip_good() again. */
>>>>> 	unsigned long now = jiffies;
>>>>>
>>>>> 	if (chip_good(map, adr, datum)) {
>>>>> 		xip_enable(map, chip, adr);
>>>>> 		goto op_done;
>>>>> 	}
>>>>>
>>>>
>>>> What if thread gets pre-empted at this point and is re-scheduled
>>>> exactly after timeo jiffies have elapsed? Below check would be true
>>>> and exit loop
>>>
>>>   I think that the jiffies value now is save before chip_good() so
>>> below check would be false and not exit loop.
>>

Ok, I get it now.

>> True, I overlooked that part, and so Vignesh did. This proves one
>> thing: code is not easier to follow with your version. IMO, if we want
>> to make things clear, we should add a comment to Liujian's explaining
>> why the extra test after time_after(jiffies, timeo) is needed.
> 
> I see so I am okay with the change of Liujian-san v3 patch.
> Also agree with the comment to be added.
> 

Right, I like the current patch from Liujian, because its more
consistent with the existing code in this file.

Liujian, Could you re-post with a comment added as suggested above?

Regards
Vignesh

Patch
diff mbox series

diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c b/drivers/mtd/chips/cfi_cmdset_0002.c
index 72428b6..3da2376 100644
--- a/drivers/mtd/chips/cfi_cmdset_0002.c
+++ b/drivers/mtd/chips/cfi_cmdset_0002.c
@@ -1876,7 +1876,7 @@  static int __xipram do_write_buffer(struct map_info *map, struct flchip *chip,
 			continue;
 		}
 
-		if (time_after(jiffies, timeo) && !chip_ready(map, adr))
+		if (time_after(jiffies, timeo) && !chip_good(map, adr, datum))
 			break;
 
 		if (chip_good(map, adr, datum)) {