Patchwork PSeries: Cancel RTAS event scan before firmware flash

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Submitter Ravi K. Nittala
Date July 27, 2011, 12:09 p.m.
Message ID <20110727120801.10429.7276.stgit@localhost6.localdomain6>
Download mbox | patch
Permalink /patch/107046/
State Superseded
Headers show

Comments

Ravi K. Nittala - July 27, 2011, 12:09 p.m.
The firmware flash update is conducted using an RTAS call, that is serialized
by lock_rtas() which uses spin_lock. rtasd keeps scanning for the RTAS events
generated on the machine. This is performed via a delayed workqueue, invoking
an RTAS call to scan the events.

The flash update takes a while to complete and during this time, any other
RTAS call has to wait. In this case, rtas_event_scan() waits for a long time
on the spin_lock resulting in a soft lockup.

Approaches to fix the issue :

Approach 1: Stop all the other CPUs before we start flashing the firmware.

Before the rtas firmware update starts, all other CPUs should be stopped.
Which means no other CPU should be in lock_rtas(). We do not want other CPUs
execute while FW update is in progress and the system will be rebooted anyway
after the update.
Suzuki Poulose - Aug. 8, 2011, 6:46 a.m.
On 07/27/11 17:39, Ravi K. Nittala wrote:
> The firmware flash update is conducted using an RTAS call, that is serialized
> by lock_rtas() which uses spin_lock. rtasd keeps scanning for the RTAS events
> generated on the machine. This is performed via a delayed workqueue, invoking
> an RTAS call to scan the events.
>
> The flash update takes a while to complete and during this time, any other
> RTAS call has to wait. In this case, rtas_event_scan() waits for a long time
> on the spin_lock resulting in a soft lockup.
>
> Approaches to fix the issue :
>
> Approach 1: Stop all the other CPUs before we start flashing the firmware.
>
> Before the rtas firmware update starts, all other CPUs should be stopped.
> Which means no other CPU should be in lock_rtas(). We do not want other CPUs
> execute while FW update is in progress and the system will be rebooted anyway
> after the update.
>
> --- arch/powerpc/kernel/setup-common.c.orig    2011-07-01 22:41:12.952507971 -0400
> +++ arch/powerpc/kernel/setup-common.c    2011-07-01 22:48:31.182507915 -0400
> @@ -109,11 +109,12 @@ void machine_shutdown(void)
>    void machine_restart(char *cmd)
>    {
>        machine_shutdown();
> -    if (ppc_md.restart)
> -        ppc_md.restart(cmd);
>    #ifdef CONFIG_SMP
> -    smp_send_stop();
> +        smp_send_stop();
>    #endif
> +    if (ppc_md.restart)
> +        ppc_md.restart(cmd);
> +
>        printk(KERN_EMERG "System Halted, OK to turn off power\n");
>        local_irq_disable();
>        while (1) ;
>
> Problems with this approach:
> Stopping the CPUs suddenly may cause other serious problems depending on what
> was running on them. Hence, this approach cannot be considered.
>
>
> Approach 2: Cancel the rtas_scan_event work before starting the firmware flash.
>
> Just before the flash update is performed, the queued rtas_event_scan() work
> item is cancelled from the work queue so that there is no other RTAS call
> issued while the flash is in progress. After the flash completes, the system
> reboots and the rtas_event_scan() is rescheduled.
>
> Approach 2 looks to be a better solution than Approach 1. Kindly let us know
> your thoughts. Patch attached.
>

Ben,

Could you please let us know your thoughts about the following patch ?

Thanks
Suzuki


>
> Signed-off-by: Suzuki Poulose<suzuki@in.ibm.com>
> Signed-off-by: Ravi Nittala<ravi.nittala@in.ibm.com>
>
>
> ---
>   arch/powerpc/include/asm/rtas.h  |    2 ++
>   arch/powerpc/kernel/rtas_flash.c |    6 ++++++
>   arch/powerpc/kernel/rtasd.c      |    6 ++++++
>   3 files changed, 14 insertions(+), 0 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/rtas.h b/arch/powerpc/include/asm/rtas.h
> index 58625d1..3f26f87 100644
> --- a/arch/powerpc/include/asm/rtas.h
> +++ b/arch/powerpc/include/asm/rtas.h
> @@ -245,6 +245,8 @@ extern int early_init_dt_scan_rtas(unsigned long node,
>
>   extern void pSeries_log_error(char *buf, unsigned int err_type, int fatal);
>
> +extern bool rtas_cancel_event_scan(void);
> +
>   /* Error types logged.  */
>   #define ERR_FLAG_ALREADY_LOGGED	0x0
>   #define ERR_FLAG_BOOT		0x1 	/* log was pulled from NVRAM on boot */
> diff --git a/arch/powerpc/kernel/rtas_flash.c b/arch/powerpc/kernel/rtas_flash.c
> index e037c74..4174b4b 100644
> --- a/arch/powerpc/kernel/rtas_flash.c
> +++ b/arch/powerpc/kernel/rtas_flash.c
> @@ -568,6 +568,12 @@ static void rtas_flash_firmware(int reboot_type)
>   	}
>
>   	/*
> +	 * Just before starting the firmware flash, cancel the event scan work
> +	 * to avoid any soft lockup issues.
> +	 */
> +	rtas_cancel_event_scan();
> +
> +	/*
>   	 * NOTE: the "first" block must be under 4GB, so we create
>   	 * an entry with no data blocks in the reserved buffer in
>   	 * the kernel data segment.
> diff --git a/arch/powerpc/kernel/rtasd.c b/arch/powerpc/kernel/rtasd.c
> index 481ef06..e8f03fa 100644
> --- a/arch/powerpc/kernel/rtasd.c
> +++ b/arch/powerpc/kernel/rtasd.c
> @@ -472,6 +472,12 @@ static void start_event_scan(void)
>   				&event_scan_work, event_scan_delay);
>   }
>
> +/* Cancel the rtas event scan work */
> +bool rtas_cancel_event_scan(void)
> +{
> +	return cancel_delayed_work_sync(&event_scan_work);
> +}
> +
>   static int __init rtas_init(void)
>   {
>   	struct proc_dir_entry *entry;
>
Benjamin Herrenschmidt - Aug. 30, 2011, 6:03 a.m.
On Wed, 2011-07-27 at 17:39 +0530, Ravi K. Nittala wrote:
> The firmware flash update is conducted using an RTAS call, that is serialized
> by lock_rtas() which uses spin_lock. rtasd keeps scanning for the RTAS events
> generated on the machine. This is performed via a delayed workqueue, invoking
> an RTAS call to scan the events.
> 
> The flash update takes a while to complete and during this time, any other
> RTAS call has to wait. In this case, rtas_event_scan() waits for a long time
> on the spin_lock resulting in a soft lockup.
> 
> Approaches to fix the issue :
> 
> Approach 1: Stop all the other CPUs before we start flashing the firmware.
> 
> Before the rtas firmware update starts, all other CPUs should be stopped.
> Which means no other CPU should be in lock_rtas(). We do not want other CPUs
> execute while FW update is in progress and the system will be rebooted anyway
> after the update.

Shouldn't we resume the event scan after the flash ?

Appart from that, no objection with the approach.

Cheers,
Ben.

> --- arch/powerpc/kernel/setup-common.c.orig    2011-07-01 22:41:12.952507971 -0400
> +++ arch/powerpc/kernel/setup-common.c    2011-07-01 22:48:31.182507915 -0400
> @@ -109,11 +109,12 @@ void machine_shutdown(void)
>   void machine_restart(char *cmd)
>   {
>       machine_shutdown();
> -    if (ppc_md.restart)
> -        ppc_md.restart(cmd);
>   #ifdef CONFIG_SMP
> -    smp_send_stop();
> +        smp_send_stop();
>   #endif
> +    if (ppc_md.restart)
> +        ppc_md.restart(cmd);
> +
>       printk(KERN_EMERG "System Halted, OK to turn off power\n");
>       local_irq_disable();
>       while (1) ;
> 
> Problems with this approach:
> Stopping the CPUs suddenly may cause other serious problems depending on what
> was running on them. Hence, this approach cannot be considered.
> 
> 
> Approach 2: Cancel the rtas_scan_event work before starting the firmware flash.
> 
> Just before the flash update is performed, the queued rtas_event_scan() work
> item is cancelled from the work queue so that there is no other RTAS call
> issued while the flash is in progress. After the flash completes, the system
> reboots and the rtas_event_scan() is rescheduled.
> 
> Approach 2 looks to be a better solution than Approach 1. Kindly let us know
> your thoughts. Patch attached.
> 
> 
> Signed-off-by: Suzuki Poulose <suzuki@in.ibm.com>
> Signed-off-by: Ravi Nittala <ravi.nittala@in.ibm.com>
> 
> 
> ---
>  arch/powerpc/include/asm/rtas.h  |    2 ++
>  arch/powerpc/kernel/rtas_flash.c |    6 ++++++
>  arch/powerpc/kernel/rtasd.c      |    6 ++++++
>  3 files changed, 14 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/rtas.h b/arch/powerpc/include/asm/rtas.h
> index 58625d1..3f26f87 100644
> --- a/arch/powerpc/include/asm/rtas.h
> +++ b/arch/powerpc/include/asm/rtas.h
> @@ -245,6 +245,8 @@ extern int early_init_dt_scan_rtas(unsigned long node,
>  
>  extern void pSeries_log_error(char *buf, unsigned int err_type, int fatal);
>  
> +extern bool rtas_cancel_event_scan(void);
> +
>  /* Error types logged.  */
>  #define ERR_FLAG_ALREADY_LOGGED	0x0
>  #define ERR_FLAG_BOOT		0x1 	/* log was pulled from NVRAM on boot */
> diff --git a/arch/powerpc/kernel/rtas_flash.c b/arch/powerpc/kernel/rtas_flash.c
> index e037c74..4174b4b 100644
> --- a/arch/powerpc/kernel/rtas_flash.c
> +++ b/arch/powerpc/kernel/rtas_flash.c
> @@ -568,6 +568,12 @@ static void rtas_flash_firmware(int reboot_type)
>  	}
>  
>  	/*
> +	 * Just before starting the firmware flash, cancel the event scan work
> +	 * to avoid any soft lockup issues.
> +	 */
> +	rtas_cancel_event_scan();
> +
> +	/*
>  	 * NOTE: the "first" block must be under 4GB, so we create
>  	 * an entry with no data blocks in the reserved buffer in
>  	 * the kernel data segment.
> diff --git a/arch/powerpc/kernel/rtasd.c b/arch/powerpc/kernel/rtasd.c
> index 481ef06..e8f03fa 100644
> --- a/arch/powerpc/kernel/rtasd.c
> +++ b/arch/powerpc/kernel/rtasd.c
> @@ -472,6 +472,12 @@ static void start_event_scan(void)
>  				 &event_scan_work, event_scan_delay);
>  }
>  
> +/* Cancel the rtas event scan work */
> +bool rtas_cancel_event_scan(void)
> +{
> +	return cancel_delayed_work_sync(&event_scan_work);
> +}
> +
>  static int __init rtas_init(void)
>  {
>  	struct proc_dir_entry *entry;
> 
> _______________________________________________
> Linuxppc-dev mailing list
> Linuxppc-dev@lists.ozlabs.org
> https://lists.ozlabs.org/listinfo/linuxppc-dev
Suzuki Poulose - Aug. 30, 2011, 6:17 a.m.
On 08/30/11 11:33, Benjamin Herrenschmidt wrote:
> On Wed, 2011-07-27 at 17:39 +0530, Ravi K. Nittala wrote:
>> The firmware flash update is conducted using an RTAS call, that is serialized
>> by lock_rtas() which uses spin_lock. rtasd keeps scanning for the RTAS events
>> generated on the machine. This is performed via a delayed workqueue, invoking
>> an RTAS call to scan the events.
>>
>> The flash update takes a while to complete and during this time, any other
>> RTAS call has to wait. In this case, rtas_event_scan() waits for a long time
>> on the spin_lock resulting in a soft lockup.
>>
>> Approaches to fix the issue :
>>
>> Approach 1: Stop all the other CPUs before we start flashing the firmware.
>>
>> Before the rtas firmware update starts, all other CPUs should be stopped.
>> Which means no other CPU should be in lock_rtas(). We do not want other CPUs
>> execute while FW update is in progress and the system will be rebooted anyway
>> after the update.
>
> Shouldn't we resume the event scan after the flash ?
>

The flash operation is performed in the reboot path at the very end.
So, even if we restart the event scan, the thread may not be able to process
the events. Hence we thought we would leave it stopped.

Again, we do not have much expertise in deciding which is the best thing to do.
We could resume the event scan, if you think that is needed.

Thanks for the review.

Suzuki
Benjamin Herrenschmidt - Aug. 30, 2011, 6:19 a.m.
On Tue, 2011-08-30 at 11:47 +0530, Suzuki Poulose wrote:
> >
> 
> The flash operation is performed in the reboot path at the very end.
> So, even if we restart the event scan, the thread may not be able to
> process
> the events. Hence we thought we would leave it stopped.
> 
> Again, we do not have much expertise in deciding which is the best
> thing to do.
> We could resume the event scan, if you think that is needed.
> 
> Thanks for the review. 

No that's ok, I'll merge the patch as-is then.

Cheers,
Ben.
Benjamin Herrenschmidt - Aug. 30, 2011, 6:21 a.m.
On Tue, 2011-08-30 at 16:19 +1000, Benjamin Herrenschmidt wrote:
> On Tue, 2011-08-30 at 11:47 +0530, Suzuki Poulose wrote:
> > >
> > 
> > The flash operation is performed in the reboot path at the very end.
> > So, even if we restart the event scan, the thread may not be able to
> > process
> > the events. Hence we thought we would leave it stopped.
> > 
> > Again, we do not have much expertise in deciding which is the best
> > thing to do.
> > We could resume the event scan, if you think that is needed.
> > 
> > Thanks for the review. 
> 
> No that's ok, I'll merge the patch as-is then.

Actually, please dbl check you get the dependencies right. The event
scan stuff is only compiled if CONFIG_PPC_RTAS_DAEMON is set, but the
rtas flash code depends on a different config option that can be set
independently.

So at the very least you need an ifdef to guard the cross-call

Cheers,
Ben.
Suzuki Poulose - Aug. 30, 2011, 6:57 a.m.
On 08/30/11 11:51, Benjamin Herrenschmidt wrote:
> On Tue, 2011-08-30 at 16:19 +1000, Benjamin Herrenschmidt wrote:
>> On Tue, 2011-08-30 at 11:47 +0530, Suzuki Poulose wrote:
>>>>
>>>
>>> The flash operation is performed in the reboot path at the very end.
>>> So, even if we restart the event scan, the thread may not be able to
>>> process
>>> the events. Hence we thought we would leave it stopped.
>>>
>>> Again, we do not have much expertise in deciding which is the best
>>> thing to do.
>>> We could resume the event scan, if you think that is needed.
>>>
>>> Thanks for the review.
>>
>> No that's ok, I'll merge the patch as-is then.
>
> Actually, please dbl check you get the dependencies right. The event
> scan stuff is only compiled if CONFIG_PPC_RTAS_DAEMON is set, but the
> rtas flash code depends on a different config option that can be set
> independently.
>
> So at the very least you need an ifdef to guard the cross-call

Thanks for catching this ! Will address this in the next version.

Thanks
Suzuki

Patch

--- arch/powerpc/kernel/setup-common.c.orig    2011-07-01 22:41:12.952507971 -0400
+++ arch/powerpc/kernel/setup-common.c    2011-07-01 22:48:31.182507915 -0400
@@ -109,11 +109,12 @@  void machine_shutdown(void)
  void machine_restart(char *cmd)
  {
      machine_shutdown();
-    if (ppc_md.restart)
-        ppc_md.restart(cmd);
  #ifdef CONFIG_SMP
-    smp_send_stop();
+        smp_send_stop();
  #endif
+    if (ppc_md.restart)
+        ppc_md.restart(cmd);
+
      printk(KERN_EMERG "System Halted, OK to turn off power\n");
      local_irq_disable();
      while (1) ;

Problems with this approach:
Stopping the CPUs suddenly may cause other serious problems depending on what
was running on them. Hence, this approach cannot be considered.


Approach 2: Cancel the rtas_scan_event work before starting the firmware flash.

Just before the flash update is performed, the queued rtas_event_scan() work
item is cancelled from the work queue so that there is no other RTAS call
issued while the flash is in progress. After the flash completes, the system
reboots and the rtas_event_scan() is rescheduled.

Approach 2 looks to be a better solution than Approach 1. Kindly let us know
your thoughts. Patch attached.


Signed-off-by: Suzuki Poulose <suzuki@in.ibm.com>
Signed-off-by: Ravi Nittala <ravi.nittala@in.ibm.com>


---
 arch/powerpc/include/asm/rtas.h  |    2 ++
 arch/powerpc/kernel/rtas_flash.c |    6 ++++++
 arch/powerpc/kernel/rtasd.c      |    6 ++++++
 3 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/include/asm/rtas.h b/arch/powerpc/include/asm/rtas.h
index 58625d1..3f26f87 100644
--- a/arch/powerpc/include/asm/rtas.h
+++ b/arch/powerpc/include/asm/rtas.h
@@ -245,6 +245,8 @@  extern int early_init_dt_scan_rtas(unsigned long node,
 
 extern void pSeries_log_error(char *buf, unsigned int err_type, int fatal);
 
+extern bool rtas_cancel_event_scan(void);
+
 /* Error types logged.  */
 #define ERR_FLAG_ALREADY_LOGGED	0x0
 #define ERR_FLAG_BOOT		0x1 	/* log was pulled from NVRAM on boot */
diff --git a/arch/powerpc/kernel/rtas_flash.c b/arch/powerpc/kernel/rtas_flash.c
index e037c74..4174b4b 100644
--- a/arch/powerpc/kernel/rtas_flash.c
+++ b/arch/powerpc/kernel/rtas_flash.c
@@ -568,6 +568,12 @@  static void rtas_flash_firmware(int reboot_type)
 	}
 
 	/*
+	 * Just before starting the firmware flash, cancel the event scan work
+	 * to avoid any soft lockup issues.
+	 */
+	rtas_cancel_event_scan();
+
+	/*
 	 * NOTE: the "first" block must be under 4GB, so we create
 	 * an entry with no data blocks in the reserved buffer in
 	 * the kernel data segment.
diff --git a/arch/powerpc/kernel/rtasd.c b/arch/powerpc/kernel/rtasd.c
index 481ef06..e8f03fa 100644
--- a/arch/powerpc/kernel/rtasd.c
+++ b/arch/powerpc/kernel/rtasd.c
@@ -472,6 +472,12 @@  static void start_event_scan(void)
 				 &event_scan_work, event_scan_delay);
 }
 
+/* Cancel the rtas event scan work */
+bool rtas_cancel_event_scan(void)
+{
+	return cancel_delayed_work_sync(&event_scan_work);
+}
+
 static int __init rtas_init(void)
 {
 	struct proc_dir_entry *entry;