From: Seiji Aguchi <seiji.aguchi@hds.com>
Date: Fri, 11 Jan 2013 18:10:05 +0000 (+0000)
Subject: efi_pstore: Avoid deadlock in non-blocking paths
X-Git-Tag: v3.9-rc1~130^2~3
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e59310adf5eebce108f78b6c47bb330aae2e1666;p=pandora-kernel.git

efi_pstore: Avoid deadlock in non-blocking paths

[Issue]

There is a scenario which efi_pstore may hang up:

 - cpuA grabs efivars->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 efivars->lock
 - cpuB is deadlocked

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

[Solution]

This patch changes a spin_lock to a spin_trylock in non-blocking paths.
and if the spin_lock has already taken by another cpu,
it returns without accessing to a firmware to avoid the deadlock.

Signed-off-by: Seiji Aguchi <seiji.aguchi@hds.com>
Acked-by: Don Zickus <dzickus@redhat.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
---

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