Messages in this thread Patch in this message | | | From | Seiji Aguchi <> | Subject | [PATCH v2 2/2] efi_pstore: Avoid deadlock in non-blocking paths | Date | Mon, 17 Dec 2012 20:57:52 +0000 |
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[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> --- drivers/firmware/efivars.c | 11 ++++++++++- fs/pstore/platform.c | 6 +++--- include/linux/pstore.h | 6 ++++++ 3 files changed, 19 insertions(+), 4 deletions(-)
diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c index 52c5d89..25d464e 100644 --- a/drivers/firmware/efivars.c +++ b/drivers/firmware/efivars.c @@ -1210,7 +1210,16 @@ 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_is_non_blocking_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. diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c index b87d1de..f959eba 100644 --- a/fs/pstore/platform.c +++ b/fs/pstore/platform.c @@ -96,7 +96,7 @@ static const char *get_reason_str(enum kmsg_dump_reason reason) } } -static bool is_non_blocking_path(enum kmsg_dump_reason reason) +bool pstore_is_non_blocking_path(enum kmsg_dump_reason reason) { /* * In case of NMI path, pstore shouldn't be blocked @@ -134,7 +134,7 @@ static void pstore_dump(struct kmsg_dumper *dumper, why = get_reason_str(reason); - if (is_non_blocking_path(reason)) { + if (pstore_is_non_blocking_path(reason)) { is_locked = spin_trylock_irqsave(&psinfo->buf_lock, flags); if (!is_locked) { pr_err("pstore dump routine blocked in %s path, may corrupt error record\n" @@ -165,7 +165,7 @@ static void pstore_dump(struct kmsg_dumper *dumper, total += hsize + len; part++; } - if (is_non_blocking_path(reason)) { + if (pstore_is_non_blocking_path(reason)) { if (is_locked) spin_unlock_irqrestore(&psinfo->buf_lock, flags); } else diff --git a/include/linux/pstore.h b/include/linux/pstore.h index 1788909..595a040 100644 --- a/include/linux/pstore.h +++ b/include/linux/pstore.h @@ -68,12 +68,18 @@ struct pstore_info { #ifdef CONFIG_PSTORE extern int pstore_register(struct pstore_info *); +extern bool pstore_is_non_blocking_path(enum kmsg_dump_reason reason); #else static inline int pstore_register(struct pstore_info *psi) { return -ENODEV; } +static inline bool +pstore_is_non_blocking_path(enum kmsg_dump_reason reason) +{ + return false; +} #endif #endif /*_LINUX_PSTORE_H*/ -- 1.7.1
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