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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>
This commit is contained in:
Seiji Aguchi 2013-01-11 18:10:05 +00:00 committed by Tony Luck
parent 9f244e9cfd
commit e59310adf5
1 changed files with 10 additions and 1 deletions
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11
drivers/firmware/efivars.c
View File

@ -1209,7 +1209,16 @@ static int efi_pstore_write(enum pstore_type_id type,
u64 storage_space, remaining_space, max_variable_size;
efi_status_t status = EFI_NOT_FOUND;
spin_lock(&efivars->lock);
if (pstore_cannot_block_path(reason)) {
/*
* If the lock is taken by another cpu in non-blocking path,
* this driver returns without entering firmware to avoid
* hanging up.
*/
if (!spin_trylock(&efivars->lock))
return -EBUSY;
} else
spin_lock(&efivars->lock);
/*
* Check if there is a space enough to log.