Commit 5b31044e authored by Harry Yoo (Oracle)'s avatar Harry Yoo (Oracle) Committed by Vlastimil Babka (SUSE)
Browse files

mm/slab: return NULL early from kmalloc_nolock() in NMI on UP 

On UP kernels (!CONFIG_SMP), spin_trylock() is a no-op that
unconditionally succeeds even when the lock is already held. As a
result, kmalloc_nolock() called from NMI context can re-enter the slab
allocator and acquire n->list_lock that the interrupted context is
already holding, corrupting slab state.

With CONFIG_DEBUG_SPINLOCK on UP, the following BUG is triggered with
the slub_kunit test module:

  BUG: spinlock trylock failure on UP on CPU#0, kunit_try_catch/243
  [...]
  Call Trace:
   <NMI>
   dump_stack_lvl+0x3f/0x60
   do_raw_spin_trylock+0x41/0x50
   _raw_spin_trylock+0x24/0x50
   get_from_partial_node+0x120/0x4d0
   ___slab_alloc+0x8a/0x4c0
   kmalloc_nolock_noprof+0x164/0x310
   [...]
   </NMI>

Fix this by returning NULL early when invoked from NMI on a UP kernel.

Link: https://lore.kernel.org/linux-mm/ad_cqe51pvr1WaDg@hyeyoo


Cc: stable@vger.kernel.org
Fixes: af92793e ("slab: Introduce kmalloc_nolock() and kfree_nolock().")
Signed-off-by: default avatarHarry Yoo (Oracle) <harry@kernel.org>
Link: https://patch.msgid.link/20260427-nolock-api-fix-v2-2-a6b83a92d9a4@kernel.org


Signed-off-by: default avatarVlastimil Babka (SUSE) <vbabka@kernel.org>
parent 620b46ed

mm/slub.c

+4 −0
Original line number Diff line number Diff line
@@ -5339,6 +5339,10 @@ void *kmalloc_nolock_noprof(size_t size, gfp_t gfp_flags, int node) 
	if (IS_ENABLED(CONFIG_PREEMPT_RT) && (in_nmi() || in_hardirq()))

		return NULL;



	/* On UP, spin_trylock() always succeeds even when it is locked */

	if (!IS_ENABLED(CONFIG_SMP) && in_nmi())

		return NULL;



retry:

	if (unlikely(size > KMALLOC_MAX_CACHE_SIZE))

		return NULL;