From e59310adf5eebce108f78b6c47bb330aae2e1666 Mon Sep 17 00:00:00 2001 From: Seiji Aguchi Date: Fri, 11 Jan 2013 18:10:05 +0000 Subject: [PATCH] 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 Acked-by: Don Zickus Signed-off-by: Tony Luck --- drivers/firmware/efivars.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c index 7b1c37497c9a..ef5070d86f88 100644 --- a/drivers/firmware/efivars.c +++ b/drivers/firmware/efivars.c @@ -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. -- 2.20.1