From: Swaraj Gaikwad Date: Tue, 13 Jan 2026 15:06:39 +0000 (+0530) Subject: slab: fix kmalloc_nolock() context check for PREEMPT_RT X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=99a3e3a1cfc93b8fe318c0a3a5cfb01f1d4ad53c;p=thirdparty%2Flinux.git slab: fix kmalloc_nolock() context check for PREEMPT_RT On PREEMPT_RT kernels, local_lock becomes a sleeping lock. The current check in kmalloc_nolock() only verifies we're not in NMI or hard IRQ context, but misses the case where preemption is disabled. When a BPF program runs from a tracepoint with preemption disabled (preempt_count > 0), kmalloc_nolock() proceeds to call local_lock_irqsave() which attempts to acquire a sleeping lock, triggering: BUG: sleeping function called from invalid context in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 6128 preempt_count: 2, expected: 0 Fix this by checking !preemptible() on PREEMPT_RT, which directly expresses the constraint that we cannot take a sleeping lock when preemption is disabled. This encompasses the previous checks for NMI and hard IRQ contexts while also catching cases where preemption is disabled. Fixes: af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock().") Reported-by: syzbot+b1546ad4a95331b2101e@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=b1546ad4a95331b2101e Signed-off-by: Swaraj Gaikwad Acked-by: Sebastian Andrzej Siewior Acked-by: Alexei Starovoitov Acked-by: Harry Yoo Link: https://patch.msgid.link/20260113150639.48407-1-swarajgaikwad1925@gmail.co Cc: Signed-off-by: Vlastimil Babka --- diff --git a/mm/slub.c b/mm/slub.c index 861592ac5425..f77b7407c51b 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -5694,8 +5694,12 @@ void *kmalloc_nolock_noprof(size_t size, gfp_t gfp_flags, int node) if (unlikely(!size)) return ZERO_SIZE_PTR; - if (IS_ENABLED(CONFIG_PREEMPT_RT) && (in_nmi() || in_hardirq())) - /* kmalloc_nolock() in PREEMPT_RT is not supported from irq */ + if (IS_ENABLED(CONFIG_PREEMPT_RT) && !preemptible()) + /* + * kmalloc_nolock() in PREEMPT_RT is not supported from + * non-preemptible context because local_lock becomes a + * sleeping lock on RT. + */ return NULL; retry: if (unlikely(size > KMALLOC_MAX_CACHE_SIZE))