Per documentation, stack_depot_save_flags() was meant to be usable from NMI context if STACK_DEPOT_FLAG_CAN_ALLOC is unset. However, it still would try to take the pool_lock in an attempt to save a stack trace in the current pool (if space is available). This could result in deadlock if an NMI is handled while pool_lock is already held. To avoid deadlock, only try to take the lock in NMI context and give up if unsuccessful. The documentation is fixed to clearly convey this. Link: https://lkml.kernel.org/r/Z0CcyfbPqmxJ9uJH@xxxxxxxxxxxxxxxx Fixes: 4434a56ec209 ("stackdepot: make fast paths lock-less again") Reported-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Signed-off-by: Marco Elver <elver@xxxxxxxxxx> --- include/linux/stackdepot.h | 6 +++--- lib/stackdepot.c | 10 +++++++++- 2 files changed, 12 insertions(+), 4 deletions(-) diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h index e9ec32fb97d4..2cc21ffcdaf9 100644 --- a/include/linux/stackdepot.h +++ b/include/linux/stackdepot.h @@ -147,7 +147,7 @@ static inline int stack_depot_early_init(void) { return 0; } * If the provided stack trace comes from the interrupt context, only the part * up to the interrupt entry is saved. * - * Context: Any context, but setting STACK_DEPOT_FLAG_CAN_ALLOC is required if + * Context: Any context, but unsetting STACK_DEPOT_FLAG_CAN_ALLOC is required if * alloc_pages() cannot be used from the current context. Currently * this is the case for contexts where neither %GFP_ATOMIC nor * %GFP_NOWAIT can be used (NMI, raw_spin_lock). @@ -156,7 +156,7 @@ static inline int stack_depot_early_init(void) { return 0; } */ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries, unsigned int nr_entries, - gfp_t gfp_flags, + gfp_t alloc_flags, depot_flags_t depot_flags); /** @@ -175,7 +175,7 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries, * Return: Handle of the stack trace stored in depot, 0 on failure */ depot_stack_handle_t stack_depot_save(unsigned long *entries, - unsigned int nr_entries, gfp_t gfp_flags); + unsigned int nr_entries, gfp_t alloc_flags); /** * __stack_depot_get_stack_record - Get a pointer to a stack_record struct diff --git a/lib/stackdepot.c b/lib/stackdepot.c index 5ed34cc963fc..245d5b416699 100644 --- a/lib/stackdepot.c +++ b/lib/stackdepot.c @@ -630,7 +630,15 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries, prealloc = page_address(page); } - raw_spin_lock_irqsave(&pool_lock, flags); + if (in_nmi()) { + /* We can never allocate in NMI context. */ + WARN_ON_ONCE(can_alloc); + /* Best effort; bail if we fail to take the lock. */ + if (!raw_spin_trylock_irqsave(&pool_lock, flags)) + goto exit; + } else { + raw_spin_lock_irqsave(&pool_lock, flags); + } printk_deferred_enter(); /* Try to find again, to avoid concurrently inserting duplicates. */ -- 2.47.0.371.ga323438b13-goog
