From: Harry Yoo (Oracle) <harry@kernel.org>
Date: Mon, 27 Apr 2026 07:09:52 +0000 (+0900)
Subject: mm/page_alloc: return NULL early from alloc_frozen_pages_nolock() in NMI on UP
X-Git-Tag: v7.1-rc2~2^2~1
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=620b46ed6ae17c8438d889c8c0cfddab36a1476c;p=thirdparty%2Fkernel%2Flinux.git

mm/page_alloc: return NULL early from alloc_frozen_pages_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, alloc_frozen_pages_nolock() called from NMI context can
re-enter rmqueue() and acquire the zone lock that the interrupted
context is already holding, corrupting the freelists.

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
   rmqueue.isra.0+0x2a9/0xa70
   get_page_from_freelist+0xeb/0x450
   alloc_frozen_pages_nolock_noprof+0x111/0x1e0
   allocate_slab+0x42a/0x500
   ___slab_alloc+0xa7/0x4c0
   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: d7242af86434 ("mm: Introduce alloc_frozen_pages_nolock()")
Signed-off-by: Harry Yoo (Oracle) <harry@kernel.org>
Link: https://patch.msgid.link/20260427-nolock-api-fix-v2-1-a6b83a92d9a4@kernel.org
Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
---

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 111b54df8a3c..b1b1039287e9 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7775,6 +7775,11 @@ struct page *alloc_frozen_pages_nolock_noprof(gfp_t gfp_flags, int nid, unsigned
 	 */
 	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;
+
 	if (!pcp_allowed_order(order))
 		return NULL;