[PATCH v3 0/2] pstore,efi_pstore: Avoid deadlock in non-blocking paths

[PATCH v3 0/2] pstore,efi_pstore: Avoid deadlock in non-blocking paths

[Seiji Aguchi]

Changelog 
v2 -> v3
 - Merge modifications of pstore part in 2/2 to 1/2.
 - Rename pstore_is_non_blocking_path() to pstore_cannot_block_path().

v1 -> v2
 - Erase a logic checking the number of online cpus.
 - Create a patchset to fix deadlocking issue in both pstore filesystem and
   efi_pstore driver.
   - Introduce a function, is_non_blocking_path(), to check if pstore 
     is in panic and emergency-restart paths (PATCH 1/2)
   - Avoid efi_pstore_driver is blocked in non-blocking paths
     such as nmi, panic and emergency-restart paths (PATCH 2/2)

[Issue]

There are some paths in kernel which shouldn't be blocked, 
like NMI, panic case after stopping cpus, emergency-restart.

On the other hand, current pstore avoids blocking in a NMI path 
but it may be blocked in other paths.
Also, an efi_pstore driver may be blocked in all of those paths 
because it simply takes a spin lock at writing time.

If they are blocked in those paths, the system will hang up and
it has a big impact for users.

Here is an example scenario which pstore is blocked in panic path.

 - cpuA grabs psinfo->buf_lock
 - cpuB panics and calls smp_send_stop
 - smp_send_stop sends IRQ to cpuA
   after 1 second, cpuB gives up on cpuA and sends an NMI instead
 - cpuA is now in an NMI handler while still holding buf_lock.
   And then, cpuB is deadlocked by taking efi_pstore->lock again.

This case may happen if a firmware has a bug and cpuA is stuck in it.

[Solution]

This patchset avoids that pstore and efi_pstore driver are blocked 
in the non-blocking paths like NMI, panic, and emrgency-restart
by introducing a function checking if they are in those paths.
Please see each patch for detailed explanations.

Seiji Aguchi (2):
  [PATCH v3 1/2] pstore: Avoid deadlock in panic and emergency-restart path
  [PATCH v3 2/2] efi_pstore: Avoid deadlock in non-blocking paths

 drivers/firmware/efivars.c |   11 ++++++++++-
 fs/pstore/platform.c       |   34 ++++++++++++++++++++++++++++------
 include/linux/pstore.h     |    6 ++++++
 3 files changed, 44 insertions(+), 7 deletions(-)

Re: [PATCH v3 0/2] pstore,efi_pstore: Avoid deadlock in non-blocking paths

[Don Zickus]

On Thu, Dec 20, 2012 at 03:11:14PM +0000, Seiji Aguchi wrote:
> Changelog 
> v2 -> v3
>  - Merge modifications of pstore part in 2/2 to 1/2.
>  - Rename pstore_is_non_blocking_path() to pstore_cannot_block_path().
> 
> v1 -> v2
>  - Erase a logic checking the number of online cpus.
>  - Create a patchset to fix deadlocking issue in both pstore filesystem and
>    efi_pstore driver.
>    - Introduce a function, is_non_blocking_path(), to check if pstore 
>      is in panic and emergency-restart paths (PATCH 1/2)
>    - Avoid efi_pstore_driver is blocked in non-blocking paths
>      such as nmi, panic and emergency-restart paths (PATCH 2/2)
> 
> [Issue]
> 
> There are some paths in kernel which shouldn't be blocked, 
> like NMI, panic case after stopping cpus, emergency-restart.

I am ok with it.

Acked-by: Don Zickus <dzickus@redhat.com>

RE: [PATCH v3 0/2] pstore,efi_pstore: Avoid deadlock in non-blocking paths

[Seiji Aguchi]

Tony,

Could you please apply this patchset to your tree?

Seiji

> -----Original Message-----
> From: Don Zickus [mailto:dzickus@redhat.com]
> Sent: Thursday, December 20, 2012 2:09 PM
> To: Seiji Aguchi
> Cc: linux-kernel@vger.kernel.org; Luck, Tony (tony.luck@intel.com); ccross@android.com; keescook@chromium.org;
> cbouatmailru@gmail.com; Satoru Moriya; dle-develop@lists.sourceforge.net
> Subject: Re: [PATCH v3 0/2] pstore,efi_pstore: Avoid deadlock in non-blocking paths
> 
> On Thu, Dec 20, 2012 at 03:11:14PM +0000, Seiji Aguchi wrote:
> > Changelog
> > v2 -> v3
> >  - Merge modifications of pstore part in 2/2 to 1/2.
> >  - Rename pstore_is_non_blocking_path() to pstore_cannot_block_path().
> >
> > v1 -> v2
> >  - Erase a logic checking the number of online cpus.
> >  - Create a patchset to fix deadlocking issue in both pstore filesystem and
> >    efi_pstore driver.
> >    - Introduce a function, is_non_blocking_path(), to check if pstore
> >      is in panic and emergency-restart paths (PATCH 1/2)
> >    - Avoid efi_pstore_driver is blocked in non-blocking paths
> >      such as nmi, panic and emergency-restart paths (PATCH 2/2)
> >
> > [Issue]
> >
> > There are some paths in kernel which shouldn't be blocked, like NMI,
> > panic case after stopping cpus, emergency-restart.
> 
> I am ok with it.
> 
> Acked-by: Don Zickus <dzickus@redhat.com>

Re: [PATCH v3 0/2] pstore,efi_pstore: Avoid deadlock in non-blocking paths

[Anton Vorontsov]

On Fri, Dec 21, 2012 at 11:27:00PM +0000, Seiji Aguchi wrote:
> Tony,
> 
> Could you please apply this patchset to your tree?

Actually, I'd prefer to take both patches via pstore tree. The EFI part is
isolated and small, so even if it conflicts, it would be easy to resolve,
unlike to pstore core part.

So, would be great if Tony could give an Ack for EFI part and we'd merge
this via pstore tree.

Thanks,
Anton

RE: [PATCH v3 0/2] pstore,efi_pstore: Avoid deadlock in non-blocking paths

[Seiji Aguchi]

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[-- Attachment #1: Type: text/plain; charset="utf-8", Size: 1062 bytes --]

Tony,

Can you review this patchset?

Seiji

> -----Original Message-----
> From: Anton Vorontsov [mailto:cbouatmailru@gmail.com]
> Sent: Friday, December 21, 2012 6:37 PM
> To: Seiji Aguchi
> Cc: Luck, Tony (tony.luck@intel.com); linux-kernel@vger.kernel.org; ccross@android.com; keescook@chromium.org; Satoru Moriya;
> dle-develop@lists.sourceforge.net; dzickus@redhat.com
> Subject: Re: [PATCH v3 0/2] pstore,efi_pstore: Avoid deadlock in non-blocking paths
> 
> On Fri, Dec 21, 2012 at 11:27:00PM +0000, Seiji Aguchi wrote:
> > Tony,
> >
> > Could you please apply this patchset to your tree?
> 
> Actually, I'd prefer to take both patches via pstore tree. The EFI part is isolated and small, so even if it conflicts, it would be easy to
> resolve, unlike to pstore core part.
> 
> So, would be great if Tony could give an Ack for EFI part and we'd merge this via pstore tree.
> 
> Thanks,
> Anton
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