[PATCH v2 0/2] pstore,efi_pstore: Avoid deadlock in non-blockingpaths

From: Seiji Aguchi
Date: Mon Dec 17 2012 - 15:56:39 EST

Changelog 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)


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

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.


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 v2 1/2] pstore: Avoid deadlock in panic and emergency-restart path
[PATCH v2 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(-)
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/