@@ -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
@@ -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. */
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@elver.google.com Fixes: 4434a56ec209 ("stackdepot: make fast paths lock-less again") Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Marco Elver <elver@google.com> --- include/linux/stackdepot.h | 6 +++--- lib/stackdepot.c | 10 +++++++++- 2 files changed, 12 insertions(+), 4 deletions(-)