From: "Alexei Starovoitov" <alexei.starovoitov@gmail.com>
To: "Yun Lu" <luyun_611@163.com>, <daniel@iogearbox.net>,
<andrii@kernel.org>, <eddyz87@gmail.com>, <memxor@gmail.com>,
<martin.lau@linux.dev>, <song@kernel.org>,
<yonghong.song@linux.dev>, <jolsa@kernel.org>,
<emil@etsalapatis.com>, <ihor.solodrai@linux.dev>
Cc: <yatsenko@meta.com>, <bpf@vger.kernel.org>
Subject: Re: [PATCH bpf-next v3 1/2] bpf: Fix task work scheduling and callback race
Date: Wed, 23 Sep 2026 23:04:03 +0000 [thread overview]
Message-ID: <DLN2KZR6RHH5.2OO4ZIR0XA36T@gmail.com> (raw)
In-Reply-To: <20260922100042.136818-2-luyun_611@163.com>
On Tue, Sep 22, 2026 at 06:00 PM Yun Lu <luyun_611@163.com> wrote:
> - err = task_work_add(ctx->task, &ctx->work, ctx->mode);
> + task = get_task_struct(ctx->task);
> + err = task_work_add(task, &ctx->work, ctx->mode);
Why?
There should be no need for get_task_struct().
rcu_read_lock() keeps task_struct around.
bpf_task_release() is put_task_struct_rcu_user(), so the task is
freed after rcu gp and guard(rcu)() covers the whole handler.
task = ctx->task;
is enough.
The commit log still says that rcu_read_lock() "does not retain
ctx->task". why?
[...]
> + if (unlikely(irq_work_is_busy(&ctx->irq_work))) {
> + (void)cmpxchg(&ctx->state, BPF_TW_PENDING, BPF_TW_STANDBY);
> + bpf_task_work_ctx_put(ctx);
> + return ERR_PTR(-EBUSY);
> + }
This is a fix for a different bug.
Pls split it into a separate patch and describe the sequence in
its commit log the way it's done for the first one.
"publishing a false SCHEDULED state" doesn't say what breaks.
pw-bot: cr
next prev parent reply other threads:[~2026-09-23 23:04 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-22 10:00 [PATCH bpf-next v3 0/2] bpf: Fix task work scheduling race Yun Lu
2026-09-22 10:00 ` [PATCH bpf-next v3 1/2] bpf: Fix task work scheduling and callback race Yun Lu
2026-09-23 17:46 ` Mykyta Yatsenko
2026-09-23 23:04 ` Alexei Starovoitov [this message]
2026-09-24 9:55 ` luyun
2026-09-22 10:00 ` [PATCH bpf-next v3 2/2] selftests/bpf: Add task work scheduling race test Yun Lu
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