diff mbox series

[bpf] bpf: Use preempt_count() directly in bpf_send_signal_common()

Message ID 20250220042259.1583319-1-houtao@huaweicloud.com (mailing list archive)
State Accepted
Commit b4a8b5bba712a711d8ca1f7d04646db63f9c88f5
Delegated to: BPF
Headers show
Series [bpf] bpf: Use preempt_count() directly in bpf_send_signal_common() | expand

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Commit Message

Hou Tao Feb. 20, 2025, 4:22 a.m. UTC 
From: Hou Tao <houtao1@huawei.com>

bpf_send_signal_common() uses preemptible() to check whether or not the
current context is preemptible. If it is preemptible, it will use
irq_work to send the signal asynchronously instead of trying to hold a
spin-lock, because spin-lock is sleepable under PREEMPT_RT.

However, preemptible() depends on CONFIG_PREEMPT_COUNT. When
CONFIG_PREEMPT_COUNT is turned off (e.g., CONFIG_PREEMPT_VOLUNTARY=y),
!preemptible() will be evaluated as 1 and bpf_send_signal_common() will
use irq_work unconditionally.

Fix it by unfolding "!preemptible()" and using "preempt_count() != 0 ||
irqs_disabled()" instead.

Fixes: 87c544108b61 ("bpf: Send signals asynchronously if !preemptible")
Signed-off-by: Hou Tao <houtao1@huawei.com>
---
Hi,

I had reported the problem at [1], however, it seems it got lost or was
ignored. Therefore, I sent it out myself.

[1]: https://lore.kernel.org/all/94fcfa71-51c1-2130-3452-ec58aaef94d0@huaweicloud.com/

 kernel/trace/bpf_trace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

patchwork-bot+netdevbpf@kernel.org Feb. 21, 2025, 2:50 a.m. UTC | #1 
Hello:

This patch was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Thu, 20 Feb 2025 12:22:59 +0800 you wrote:
> From: Hou Tao <houtao1@huawei.com>
> 
> bpf_send_signal_common() uses preemptible() to check whether or not the
> current context is preemptible. If it is preemptible, it will use
> irq_work to send the signal asynchronously instead of trying to hold a
> spin-lock, because spin-lock is sleepable under PREEMPT_RT.
> 
> [...]

Here is the summary with links:
  - [bpf] bpf: Use preempt_count() directly in bpf_send_signal_common()
    https://git.kernel.org/bpf/bpf-next/c/b4a8b5bba712

You are awesome, thank you!
diff mbox series

Patch

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 71c1c02ca7a3e..2e6b525904d31 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -842,7 +842,7 @@  static int bpf_send_signal_common(u32 sig, enum pid_type type, struct task_struc
 	if (unlikely(is_global_init(task)))
 		return -EPERM;
 
-	if (!preemptible()) {
+	if (preempt_count() != 0 || irqs_disabled()) {
 		/* Do an early check on signal validity. Otherwise,
 		 * the error is lost in deferred irq_work.
 		 */