From 144080a5823b2dbd635acb6decf7ab23182664f3 Mon Sep 17 00:00:00 2001 From: Harry Yoo Date: Tue, 10 Feb 2026 17:18:59 +0900 Subject: [PATCH] mm/slab: do not access current->mems_allowed_seq if !allow_spin Lockdep complains when get_from_any_partial() is called in an NMI context, because current->mems_allowed_seq is seqcount_spinlock_t and not NMI-safe: ================================ WARNING: inconsistent lock state 6.19.0-rc5-kfree-rcu+ #315 Tainted: G N -------------------------------- inconsistent {INITIAL USE} -> {IN-NMI} usage. kunit_try_catch/9989 [HC1[1]:SC0[0]:HE0:SE1] takes: ffff889085799820 (&____s->seqcount#3){.-.-}-{0:0}, at: ___slab_alloc+0x58f/0xc00 {INITIAL USE} state was registered at: lock_acquire+0x185/0x320 kernel_init_freeable+0x391/0x1150 kernel_init+0x1f/0x220 ret_from_fork+0x736/0x8f0 ret_from_fork_asm+0x1a/0x30 irq event stamp: 56 hardirqs last enabled at (55): [] _raw_spin_unlock_irq+0x27/0x70 hardirqs last disabled at (56): [] __schedule+0x2a8a/0x6630 softirqs last enabled at (0): [] copy_process+0x1dc1/0x6a10 softirqs last disabled at (0): [<0000000000000000>] 0x0 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(&____s->seqcount#3); lock(&____s->seqcount#3); *** DEADLOCK *** According to Documentation/locking/seqlock.rst, seqcount_t is not NMI-safe and seqcount_latch_t should be used when read path can interrupt the write-side critical section. In this case, do not access current->mems_allowed_seq and avoid retry. Fixes: af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock().") Cc: stable@vger.kernel.org Signed-off-by: Harry Yoo Link: https://patch.msgid.link/20260210081900.329447-2-harry.yoo@oracle.com Signed-off-by: Vlastimil Babka --- mm/slub.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 11a99bd06ac75..90f0e66671300 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -3791,6 +3791,7 @@ static void *get_from_any_partial(struct kmem_cache *s, struct partial_context * struct zone *zone; enum zone_type highest_zoneidx = gfp_zone(pc->flags); unsigned int cpuset_mems_cookie; + bool allow_spin = gfpflags_allow_spinning(pc->flags); /* * The defrag ratio allows a configuration of the tradeoffs between @@ -3815,7 +3816,15 @@ static void *get_from_any_partial(struct kmem_cache *s, struct partial_context * return NULL; do { - cpuset_mems_cookie = read_mems_allowed_begin(); + /* + * read_mems_allowed_begin() accesses current->mems_allowed_seq, + * a seqcount_spinlock_t that is not NMI-safe. Do not access + * current->mems_allowed_seq and avoid retry when GFP flags + * indicate spinning is not allowed. + */ + if (allow_spin) + cpuset_mems_cookie = read_mems_allowed_begin(); + zonelist = node_zonelist(mempolicy_slab_node(), pc->flags); for_each_zone_zonelist(zone, z, zonelist, highest_zoneidx) { struct kmem_cache_node *n; @@ -3839,7 +3848,7 @@ static void *get_from_any_partial(struct kmem_cache *s, struct partial_context * } } } - } while (read_mems_allowed_retry(cpuset_mems_cookie)); + } while (allow_spin && read_mems_allowed_retry(cpuset_mems_cookie)); #endif /* CONFIG_NUMA */ return NULL; } -- 2.47.3