Patchwork [1/1] ppc64: fix missing to check all bits of _TIF_USER_WORK_MASK in preempt

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Submitter Tiejun Chen
Date Dec. 12, 2011, 9:10 a.m.
Message ID <1323681035-19350-1-git-send-email-tiejun.chen@windriver.com>
Download mbox | patch
Permalink /patch/130677/
State Superseded
Headers show

Comments

Tiejun Chen - Dec. 12, 2011, 9:10 a.m.
In entry_64.S version of ret_from_except_lite, you'll notice that
in the !preempt case, after we've checked MSR_PR we test for any
TIF flag in _TIF_USER_WORK_MASK to decide whether to go to do_work
or not. However, in the preempt case, we do a convoluted trick to
test SIGPENDING only if PR was set and always test NEED_RESCHED ...
but we forget to test any other bit of _TIF_USER_WORK_MASK !!! So
that means that with preempt, we completely fail to test for things
like single step, syscall tracing, etc...

This should be fixed as the following path:

 - Test PR. If set, go to test_work_user, else continue.

 - In test_work_user, always test for _TIF_USER_WORK_MASK to decide to
go to do_work, maybe call it do_user_work

 - In test_work_kernel, test for _TIF_KERNEL_WORK_MASK which is set to
our new flag along with NEED_RESCHED if preempt is enabled and branch to
do_kernel_work.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com>
---
 arch/powerpc/kernel/entry_64.S |   33 +++++++++++++++------------------
 1 files changed, 15 insertions(+), 18 deletions(-)
Tiejun Chen - Dec. 13, 2011, 5:01 a.m.
Tiejun Chen wrote:
> In entry_64.S version of ret_from_except_lite, you'll notice that
> in the !preempt case, after we've checked MSR_PR we test for any
> TIF flag in _TIF_USER_WORK_MASK to decide whether to go to do_work
> or not. However, in the preempt case, we do a convoluted trick to
> test SIGPENDING only if PR was set and always test NEED_RESCHED ...
> but we forget to test any other bit of _TIF_USER_WORK_MASK !!! So
> that means that with preempt, we completely fail to test for things
> like single step, syscall tracing, etc...
> 
> This should be fixed as the following path:
> 
>  - Test PR. If set, go to test_work_user, else continue.
> 
>  - In test_work_user, always test for _TIF_USER_WORK_MASK to decide to
> go to do_work, maybe call it do_user_work
> 
>  - In test_work_kernel, test for _TIF_KERNEL_WORK_MASK which is set to
> our new flag along with NEED_RESCHED if preempt is enabled and branch to
> do_kernel_work.

Ben,

Any comment for this?

Tiejun

> 
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com>
> ---
>  arch/powerpc/kernel/entry_64.S |   33 +++++++++++++++------------------
>  1 files changed, 15 insertions(+), 18 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> index d834425..9e70b9a 100644
> --- a/arch/powerpc/kernel/entry_64.S
> +++ b/arch/powerpc/kernel/entry_64.S
> @@ -571,27 +571,26 @@ _GLOBAL(ret_from_except_lite)
>  	mtmsrd	r9,1		/* Update machine state */
>  #endif /* CONFIG_PPC_BOOK3E */
>  
> -#ifdef CONFIG_PREEMPT
> -	clrrdi	r9,r1,THREAD_SHIFT	/* current_thread_info() */
> -	li	r0,_TIF_NEED_RESCHED	/* bits to check */
> -	ld	r3,_MSR(r1)
> -	ld	r4,TI_FLAGS(r9)
> -	/* Move MSR_PR bit in r3 to _TIF_SIGPENDING position in r0 */
> -	rlwimi	r0,r3,32+TIF_SIGPENDING-MSR_PR_LG,_TIF_SIGPENDING
> -	and.	r0,r4,r0	/* check NEED_RESCHED and maybe SIGPENDING */
> -	bne	do_work
> -
> -#else /* !CONFIG_PREEMPT */
>  	ld	r3,_MSR(r1)	/* Returning to user mode? */
>  	andi.	r3,r3,MSR_PR
> -	beq	restore		/* if not, just restore regs and return */
> +	bne	test_work_user
>  
> +	clrrdi	r9,r1,THREAD_SHIFT	/* current_thread_info() */
> +	li	r0,_TIF_USER_WORK_MASK
> +#ifdef CONFIG_PREEMPT
> +	ori	r0,r0,_TIF_NEED_RESCHED
> +#endif
> +	ld	r4,TI_FLAGS(r9)
> +	and.	r0,r4,r0	/* check NEED_RESCHED and maybe _TIF_USER_WORK_MASK */
> +	bne	do_kernel_work
> +	b	restore		/* if so, just restore regs and return */
> +
> +test_work_user:
>  	/* Check current_thread_info()->flags */
>  	clrrdi	r9,r1,THREAD_SHIFT
>  	ld	r4,TI_FLAGS(r9)
>  	andi.	r0,r4,_TIF_USER_WORK_MASK
> -	bne	do_work
> -#endif
> +	bne	do_user_work
>  
>  restore:
>  BEGIN_FW_FTR_SECTION
> @@ -693,10 +692,8 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
>  	b	.ret_from_except_lite		/* loop back and handle more */
>  #endif
>  
> -do_work:
> +do_kernel_work:
>  #ifdef CONFIG_PREEMPT
> -	andi.	r0,r3,MSR_PR	/* Returning to user mode? */
> -	bne	user_work
>  	/* Check that preempt_count() == 0 and interrupts are enabled */
>  	lwz	r8,TI_PREEMPT(r9)
>  	cmpwi	cr1,r8,0
> @@ -738,9 +735,9 @@ do_work:
>  	bne	1b
>  	b	restore
>  
> -user_work:
>  #endif /* CONFIG_PREEMPT */
>  
> +do_user_work:
>  	/* Enable interrupts */
>  #ifdef CONFIG_PPC_BOOK3E
>  	wrteei	1
Benjamin Herrenschmidt - Dec. 13, 2011, 5:55 a.m.
On Tue, 2011-12-13 at 13:01 +0800, tiejun.chen wrote:
> Tiejun Chen wrote:
> > In entry_64.S version of ret_from_except_lite, you'll notice that
> > in the !preempt case, after we've checked MSR_PR we test for any
> > TIF flag in _TIF_USER_WORK_MASK to decide whether to go to do_work
> > or not. However, in the preempt case, we do a convoluted trick to
> > test SIGPENDING only if PR was set and always test NEED_RESCHED ...
> > but we forget to test any other bit of _TIF_USER_WORK_MASK !!! So
> > that means that with preempt, we completely fail to test for things
> > like single step, syscall tracing, etc...
> > 
> > This should be fixed as the following path:
> > 
> >  - Test PR. If set, go to test_work_user, else continue.
> > 
> >  - In test_work_user, always test for _TIF_USER_WORK_MASK to decide to
> > go to do_work, maybe call it do_user_work
> > 
> >  - In test_work_kernel, test for _TIF_KERNEL_WORK_MASK which is set to
> > our new flag along with NEED_RESCHED if preempt is enabled and branch to
> > do_kernel_work.
> 
> Ben,
> 
> Any comment for this?

Sorry, I didn't get to review that one yet (nor reply to your newer
responses), I have very sore eyes and basically had to get off the
computer. Hopefully I'll be better tomorrow.

Cheers,
Ben.
Tiejun Chen - Dec. 13, 2011, 6:02 a.m.
Benjamin Herrenschmidt wrote:
> On Tue, 2011-12-13 at 13:01 +0800, tiejun.chen wrote:
>> Tiejun Chen wrote:
>>> In entry_64.S version of ret_from_except_lite, you'll notice that
>>> in the !preempt case, after we've checked MSR_PR we test for any
>>> TIF flag in _TIF_USER_WORK_MASK to decide whether to go to do_work
>>> or not. However, in the preempt case, we do a convoluted trick to
>>> test SIGPENDING only if PR was set and always test NEED_RESCHED ...
>>> but we forget to test any other bit of _TIF_USER_WORK_MASK !!! So
>>> that means that with preempt, we completely fail to test for things
>>> like single step, syscall tracing, etc...
>>>
>>> This should be fixed as the following path:
>>>
>>>  - Test PR. If set, go to test_work_user, else continue.
>>>
>>>  - In test_work_user, always test for _TIF_USER_WORK_MASK to decide to
>>> go to do_work, maybe call it do_user_work
>>>
>>>  - In test_work_kernel, test for _TIF_KERNEL_WORK_MASK which is set to
>>> our new flag along with NEED_RESCHED if preempt is enabled and branch to
>>> do_kernel_work.
>> Ben,
>>
>> Any comment for this?
> 
> Sorry, I didn't get to review that one yet (nor reply to your newer

I'm nothing, please do this when you're fine completely.

Thanks
Tiejun

> responses), I have very sore eyes and basically had to get off the
> computer. Hopefully I'll be better tomorrow.
> 
> Cheers,
> Ben.
Benjamin Herrenschmidt - Dec. 15, 2011, 1:04 a.m.
On Mon, 2011-12-12 at 17:10 +0800, Tiejun Chen wrote:

> -#else /* !CONFIG_PREEMPT */
>  	ld	r3,_MSR(r1)	/* Returning to user mode? */
>  	andi.	r3,r3,MSR_PR
> -	beq	restore		/* if not, just restore regs and return */
> +	bne	test_work_user
>  
> +	clrrdi	r9,r1,THREAD_SHIFT	/* current_thread_info() */
> +	li	r0,_TIF_USER_WORK_MASK

You meant _TIF_KERNEL_WORK_MASK ?

> +#ifdef CONFIG_PREEMPT
> +	ori	r0,r0,_TIF_NEED_RESCHED
> +#endif

No, include that in _TIF_KERNEL_WORK_MASK when CONFIG_PREEMPT, ie,
modify the definition of _TIF_KERNEL_WORK_MASK to include it

> +	ld	r4,TI_FLAGS(r9)
> +	and.	r0,r4,r0	/* check NEED_RESCHED and maybe _TIF_USER_WORK_MASK */

Comment is wrong after the above

> +	bne	do_kernel_work
> +	b	restore		/* if so, just restore regs and return */
> +
> +test_work_user:
>  	/* Check current_thread_info()->flags */
>  	clrrdi	r9,r1,THREAD_SHIFT
>  	ld	r4,TI_FLAGS(r9)

For better scheduling, couldn't you have preloaded the TIF flags, then
checked for PR ?

Looks like this (also replaces do_work)

IE.	ld	r3,_MSR(r1)
	clrrdi	r9,r1,THREAD_SHIFT
  	ld	r4,TI_FLAGS(r9)
 	andi.	r3,r3,MSR_PR
	bne	test_work_user
test_work_kernel:
 	andi.	r0,r4,_TIF_KERNEL_WORK_MASK
	beq+	restore
#ifdef CONFIG_PREEMPT
	/* Check if we need to preempt */
	andi.	r0,r4,_TIF_NEED_RESCHED
	beq+	2f
	lwz	r8,TI_PREEMPT(r9)
	cmpwi	cr1,r8,0
	ld	r0,SOFTE(r1)
	cmpdi	r0,0
	crandc	eq,cr1*4+eq,eq
	bne	1f
	/* ... copy comment about preempt here ... */
	li	r0,0
	stb	r0,PACASOFTIRQEN(r13)
	stb	r0,PACAHARDIRQEN(r13)
	TRACE_DISABLE_INTS
1:	bl	.preempt_schedule_irq

	/* preempt may have re-enabled and then disabled interrupts,
	 * so we may come here as soft-disabled & hard-enabled, but
	 * we really want hard disabled.
	 */ 
#ifdef CONFIG_PPC_BOOK3E
	wrteei	0
#else
	mfmsr	r10
	rldicl	r10,r10,48,1
	rotldi	r10,r10,16
	mtmsrd	r10,1
#endif
	li	r0,0
	stb	r0,PACAHARDIRQEN(r13)

	/* Re-check if we need to preempt again */
	clrrdi	r9,r1,THREAD_SHIFT
	ld	r4,TI_FLAGS(r9)
	andi.	r0,r4,_TIF_NEED_RESCHED
	bne	1b
2:
#endif /* CONFIG_PREEMPT */	
	andi.	r0,r4,_TIF_OUR_NEW_FLAG
	beq+	restore
	... handle our new flag here
	b	restore

test_work_user:
 	andi.	r0,r4,_TIF_USER_WORK_MASK
	beq+	restore
	/* ... move user_work here ... */

>  	andi.	r0,r4,_TIF_USER_WORK_MASK
> -	bne	do_work
> -#endif
> +	bne	do_user_work
>  
>  restore:
>  BEGIN_FW_FTR_SECTION
> @@ -693,10 +692,8 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
>  	b	.ret_from_except_lite		/* loop back and handle more */
>  #endif
>  
> -do_work:
> +do_kernel_work:
>  #ifdef CONFIG_PREEMPT
> -	andi.	r0,r3,MSR_PR	/* Returning to user mode? */
> -	bne	user_work
>  	/* Check that preempt_count() == 0 and interrupts are enabled */
>  	lwz	r8,TI_PREEMPT(r9)
>  	cmpwi	cr1,r8,0
> @@ -738,9 +735,9 @@ do_work:
>  	bne	1b
>  	b	restore
>  
> -user_work:
>  #endif /* CONFIG_PREEMPT */
>  
> +do_user_work:
>  	/* Enable interrupts */
>  #ifdef CONFIG_PPC_BOOK3E
>  	wrteei	1
Benjamin Herrenschmidt - May 10, 2012, 4 a.m.
On Mon, 2011-12-12 at 17:10 +0800, Tiejun Chen wrote:

>  
> -#ifdef CONFIG_PREEMPT
> -	clrrdi	r9,r1,THREAD_SHIFT	/* current_thread_info() */
> -	li	r0,_TIF_NEED_RESCHED	/* bits to check */
> -	ld	r3,_MSR(r1)
> -	ld	r4,TI_FLAGS(r9)
> -	/* Move MSR_PR bit in r3 to _TIF_SIGPENDING position in r0 */
> -	rlwimi	r0,r3,32+TIF_SIGPENDING-MSR_PR_LG,_TIF_SIGPENDING
> -	and.	r0,r4,r0	/* check NEED_RESCHED and maybe SIGPENDING */
> -	bne	do_work
> -
> -#else /* !CONFIG_PREEMPT */
>  	ld	r3,_MSR(r1)	/* Returning to user mode? */
>  	andi.	r3,r3,MSR_PR
> -	beq	restore		/* if not, just restore regs and return */
> +	bne	test_work_user

Any reason to not use restore_user / resume_kernel like ppc32 ? It might
help whoever wants to look at that code in the future if we make both
sides a bit closer :-) Not a big deal and if you prefer like this I
don't have a firm objection
 
> +	clrrdi	r9,r1,THREAD_SHIFT	/* current_thread_info() */
> +	li	r0,_TIF_USER_WORK_MASK
> +#ifdef CONFIG_PREEMPT
> +	ori	r0,r0,_TIF_NEED_RESCHED
> +#endif

Why the above ? Doesn't _TIF_USER_WORK_MASK altready contain
TIF_NEED_RESCHED ? Also this is the kernel path, I'd rather just
define something along the lines of _TIF_KERNEL_WORK_MASK.

Then, you change the definition of it based on PREEMPT, ie:

#ifdef CONFIG_PREEMPT
#define _TIF_KERNEL_WORK_MASK	_TIF_NEED_RESCHED
#else
#define _TIF_KERNEL_WORK_MASK	0
#endif

Now, that does mean that you'll have a useless test without PREEMPT
here but ... it will stop being useless as soon as you port over
the stux emulation so it's fine as a placeholder.

> +	ld	r4,TI_FLAGS(r9)
> +	and.	r0,r4,r0	/* check NEED_RESCHED and maybe _TIF_USER_WORK_MASK */
> +	bne	do_kernel_work
> +	b	restore		/* if so, just restore regs and return */
> +
> +test_work_user:
>  	/* Check current_thread_info()->flags */
>  	clrrdi	r9,r1,THREAD_SHIFT
>  	ld	r4,TI_FLAGS(r9)
>  	andi.	r0,r4,_TIF_USER_WORK_MASK
> -	bne	do_work
> -#endif
> +	bne	do_user_work
>  
>  restore:
>  BEGIN_FW_FTR_SECTION
> @@ -693,10 +692,8 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
>  	b	.ret_from_except_lite		/* loop back and handle more */
>  #endif
>  
> -do_work:
> +do_kernel_work:
>  #ifdef CONFIG_PREEMPT
> -	andi.	r0,r3,MSR_PR	/* Returning to user mode? */
> -	bne	user_work
>  	/* Check that preempt_count() == 0 and interrupts are enabled */
>  	lwz	r8,TI_PREEMPT(r9)
>  	cmpwi	cr1,r8,0
> @@ -738,9 +735,9 @@ do_work:
>  	bne	1b
>  	b	restore
>  
> -user_work:
>  #endif /* CONFIG_PREEMPT */
>  
> +do_user_work:
>  	/* Enable interrupts */
>  #ifdef CONFIG_PPC_BOOK3E
>  	wrteei	1

Patch

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index d834425..9e70b9a 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -571,27 +571,26 @@  _GLOBAL(ret_from_except_lite)
 	mtmsrd	r9,1		/* Update machine state */
 #endif /* CONFIG_PPC_BOOK3E */
 
-#ifdef CONFIG_PREEMPT
-	clrrdi	r9,r1,THREAD_SHIFT	/* current_thread_info() */
-	li	r0,_TIF_NEED_RESCHED	/* bits to check */
-	ld	r3,_MSR(r1)
-	ld	r4,TI_FLAGS(r9)
-	/* Move MSR_PR bit in r3 to _TIF_SIGPENDING position in r0 */
-	rlwimi	r0,r3,32+TIF_SIGPENDING-MSR_PR_LG,_TIF_SIGPENDING
-	and.	r0,r4,r0	/* check NEED_RESCHED and maybe SIGPENDING */
-	bne	do_work
-
-#else /* !CONFIG_PREEMPT */
 	ld	r3,_MSR(r1)	/* Returning to user mode? */
 	andi.	r3,r3,MSR_PR
-	beq	restore		/* if not, just restore regs and return */
+	bne	test_work_user
 
+	clrrdi	r9,r1,THREAD_SHIFT	/* current_thread_info() */
+	li	r0,_TIF_USER_WORK_MASK
+#ifdef CONFIG_PREEMPT
+	ori	r0,r0,_TIF_NEED_RESCHED
+#endif
+	ld	r4,TI_FLAGS(r9)
+	and.	r0,r4,r0	/* check NEED_RESCHED and maybe _TIF_USER_WORK_MASK */
+	bne	do_kernel_work
+	b	restore		/* if so, just restore regs and return */
+
+test_work_user:
 	/* Check current_thread_info()->flags */
 	clrrdi	r9,r1,THREAD_SHIFT
 	ld	r4,TI_FLAGS(r9)
 	andi.	r0,r4,_TIF_USER_WORK_MASK
-	bne	do_work
-#endif
+	bne	do_user_work
 
 restore:
 BEGIN_FW_FTR_SECTION
@@ -693,10 +692,8 @@  ALT_FTR_SECTION_END_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
 	b	.ret_from_except_lite		/* loop back and handle more */
 #endif
 
-do_work:
+do_kernel_work:
 #ifdef CONFIG_PREEMPT
-	andi.	r0,r3,MSR_PR	/* Returning to user mode? */
-	bne	user_work
 	/* Check that preempt_count() == 0 and interrupts are enabled */
 	lwz	r8,TI_PREEMPT(r9)
 	cmpwi	cr1,r8,0
@@ -738,9 +735,9 @@  do_work:
 	bne	1b
 	b	restore
 
-user_work:
 #endif /* CONFIG_PREEMPT */
 
+do_user_work:
 	/* Enable interrupts */
 #ifdef CONFIG_PPC_BOOK3E
 	wrteei	1