The patch titled
Subject: stackdepot: fix stack_depot_save_flags() in NMI context
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
stackdepot-fix-stack_depot_save_flags-in-nmi-context.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/stackdepot-fix-stack_depot_save_flags-in-nmi-context.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Marco Elver <elver@xxxxxxxxxx>
Subject: stackdepot: fix stack_depot_save_flags() in NMI context
Date: Fri, 22 Nov 2024 16:39:47 +0100
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
Link: https://lkml.kernel.org/r/20241122154051.3914732-1-elver@xxxxxxxxxx
Fixes: 4434a56ec209 ("stackdepot: make fast paths lock-less again")
Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
Reported-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/stackdepot.h | 6 +++---
lib/stackdepot.c | 10 +++++++++-
2 files changed, 12 insertions(+), 4 deletions(-)
--- a/include/linux/stackdepot.h~stackdepot-fix-stack_depot_save_flags-in-nmi-context
+++ a/include/linux/stackdepot.h
@@ -147,7 +147,7 @@ static inline int stack_depot_early_init
* 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
*/
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_fl
* 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
--- a/lib/stackdepot.c~stackdepot-fix-stack_depot_save_flags-in-nmi-context
+++ a/lib/stackdepot.c
@@ -630,7 +630,15 @@ depot_stack_handle_t stack_depot_save_fl
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. */
_
Patches currently in -mm which might be from elver@xxxxxxxxxx are
stackdepot-fix-stack_depot_save_flags-in-nmi-context.patch
