From: Mykyta Yatsenko <mykyta.yatsenko5@gmail.com>
To: bpf@vger.kernel.org, ast@kernel.org, andrii@kernel.org,
daniel@iogearbox.net, kafai@meta.com, kernel-team@meta.com,
memxor@gmail.com, eddyz87@gmail.com
Cc: Mykyta Yatsenko <yatsenko@meta.com>
Subject: [PATCH bpf-next v6 04/10] bpf: Simplify bpf_timer_cancel()
Date: Tue, 20 Jan 2026 15:59:13 +0000 [thread overview]
Message-ID: <20260120-timer_nolock-v6-4-670ffdd787b4@meta.com> (raw)
In-Reply-To: <20260120-timer_nolock-v6-0-670ffdd787b4@meta.com>
From: Mykyta Yatsenko <yatsenko@meta.com>
Remove lock from the bpf_timer_cancel() helper. The lock does not
protect from concurrent modification of the bpf_async_cb data fields as
those are modified in the callback without locking.
Use guard(rcu)() instead of pair of explicit lock()/unlock().
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
---
kernel/bpf/helpers.c | 27 +++++++++++----------------
1 file changed, 11 insertions(+), 16 deletions(-)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 66424bc5b86137599990957ad2300110b4977df9..61ba4f6b741cc05b4a7a73a0322a23874bfd8e83 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1471,7 +1471,7 @@ static const struct bpf_func_proto bpf_timer_start_proto = {
.arg3_type = ARG_ANYTHING,
};
-BPF_CALL_1(bpf_timer_cancel, struct bpf_async_kern *, timer)
+BPF_CALL_1(bpf_timer_cancel, struct bpf_async_kern *, async)
{
struct bpf_hrtimer *t, *cur_t;
bool inc = false;
@@ -1479,13 +1479,12 @@ BPF_CALL_1(bpf_timer_cancel, struct bpf_async_kern *, timer)
if (in_nmi())
return -EOPNOTSUPP;
- rcu_read_lock();
- __bpf_spin_lock_irqsave(&timer->lock);
- t = timer->timer;
- if (!t) {
- ret = -EINVAL;
- goto out;
- }
+
+ guard(rcu)();
+
+ t = READ_ONCE(async->timer);
+ if (!t)
+ return -EINVAL;
cur_t = this_cpu_read(hrtimer_running);
if (cur_t == t) {
@@ -1493,8 +1492,7 @@ BPF_CALL_1(bpf_timer_cancel, struct bpf_async_kern *, timer)
* its own timer the hrtimer_cancel() will deadlock
* since it waits for callback_fn to finish.
*/
- ret = -EDEADLK;
- goto out;
+ return -EDEADLK;
}
/* Only account in-flight cancellations when invoked from a timer
@@ -1517,20 +1515,17 @@ BPF_CALL_1(bpf_timer_cancel, struct bpf_async_kern *, timer)
* cancelling and waiting for it synchronously, since it might
* do the same. Bail!
*/
- ret = -EDEADLK;
- goto out;
+ atomic_dec(&t->cancelling);
+ return -EDEADLK;
}
drop:
bpf_async_update_prog_callback(&t->cb, NULL, NULL);
-out:
- __bpf_spin_unlock_irqrestore(&timer->lock);
/* Cancel the timer and wait for associated callback to finish
* if it was running.
*/
- ret = ret ?: hrtimer_cancel(&t->timer);
+ ret = hrtimer_cancel(&t->timer);
if (inc)
atomic_dec(&t->cancelling);
- rcu_read_unlock();
return ret;
}
--
2.52.0
next prev parent reply other threads:[~2026-01-20 15:59 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-20 15:59 [PATCH bpf-next v6 00/10] bpf: Avoid locks in bpf_timer and bpf_wq Mykyta Yatsenko
2026-01-20 15:59 ` [PATCH bpf-next v6 01/10] bpf: Factor out timer deletion helper Mykyta Yatsenko
2026-01-20 15:59 ` [PATCH bpf-next v6 02/10] bpf: Remove unnecessary arguments from bpf_async_set_callback() Mykyta Yatsenko
2026-01-20 15:59 ` [PATCH bpf-next v6 03/10] bpf: Introduce lock-free bpf_async_update_prog_callback() Mykyta Yatsenko
2026-01-20 15:59 ` Mykyta Yatsenko [this message]
2026-01-20 15:59 ` [PATCH bpf-next v6 05/10] bpf: Enable bpf timer and workqueue use in NMI Mykyta Yatsenko
2026-01-20 18:31 ` Andrii Nakryiko
2026-01-20 21:17 ` Mykyta Yatsenko
2026-01-21 0:26 ` Andrii Nakryiko
2026-01-20 15:59 ` [PATCH bpf-next v6 06/10] bpf: Add verifier support for bpf_timer argument in kfuncs Mykyta Yatsenko
2026-01-20 15:59 ` [PATCH bpf-next v6 07/10] bpf: Introduce bpf_timer_cancel_async() kfunc Mykyta Yatsenko
2026-01-20 15:59 ` [PATCH bpf-next v6 08/10] selftests/bpf: Refactor timer selftests Mykyta Yatsenko
2026-01-20 15:59 ` [PATCH bpf-next v6 09/10] selftests/bpf: Add stress test for timer async cancel Mykyta Yatsenko
2026-01-20 15:59 ` [PATCH bpf-next v6 10/10] selftests/bpf: Verify bpf_timer_cancel_async works Mykyta Yatsenko
2026-01-21 2:30 ` [PATCH bpf-next v6 00/10] bpf: Avoid locks in bpf_timer and bpf_wq patchwork-bot+netdevbpf
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