From 031e04bdc834cda3b054ef6b698503b2b97e8186 Mon Sep 17 00:00:00 2001 From: Marco Elver Date: Fri, 22 Nov 2024 16:39:47 +0100 Subject: stackdepot: fix stack_depot_save_flags() in NMI context 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 Link: https://lkml.kernel.org/r/20241122154051.3914732-1-elver@google.com Fixes: 4434a56ec209 ("stackdepot: make fast paths lock-less again") Signed-off-by: Marco Elver Reported-by: Sebastian Andrzej Siewior Reviewed-by: Sebastian Andrzej Siewior Cc: Alexander Potapenko Cc: Andrey Konovalov Cc: Dmitry Vyukov Cc: Oscar Salvador Cc: Vlastimil Babka Cc: Signed-off-by: Andrew Morton --- lib/stackdepot.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) (limited to 'lib/stackdepot.c') 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. */ -- cgit v1.2.3