Commit 99a3e3a1 authored by Swaraj Gaikwad's avatar Swaraj Gaikwad Committed by Vlastimil Babka
Browse files

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: af92793e ("slab: Introduce kmalloc_nolock() and kfree_nolock().")
Reported-by: default avatar <syzbot+b1546ad4a95331b2101e@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=b1546ad4a95331b2101e


Signed-off-by: default avatarSwaraj Gaikwad <swarajgaikwad1925@gmail.com>
Acked-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarHarry Yoo <harry.yoo@oracle.com>
Link: https://patch.msgid.link/20260113150639.48407-1-swarajgaikwad1925@gmail.co


Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
parent 0f61b186

mm/slub.c

+6 −2
Original line number Diff line number Diff line
@@ -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))