From: Oleg Nesterov <oleg@redhat.com>
To: Sebastian Sewior <bigeasy@linutronix.de>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Peter Ziljstra <peterz@infradead.org>,
Alexei Starovoitov <alexei.starovoitov@gmail.com>,
Andrii Nakryiko <andrii@kernel.org>, bpf <bpf@vger.kernel.org>,
Jiri Olsa <jolsa@kernel.org>,
Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: uprobe splat in PREEMP_RT
Date: Wed, 2 Apr 2025 14:18:51 +0200 [thread overview]
Message-ID: <20250402121850.GI22091@redhat.com> (raw)
In-Reply-To: <20250402121315.UdZVK1JE@linutronix.de>
On 04/02, Sebastian Sewior wrote:
>
> On 2025-04-02 13:23:09 [+0200], Oleg Nesterov wrote:
> > On 04/02, Sebastian Sewior wrote:
> > >
> > > On 2025-04-02 12:33:55 [+0200], Oleg Nesterov wrote:
> > > >
> > > > The "writer" ri_timer() can't race with itself, right?
> > >
> > > On PREEMPT_RT the timer could be preempted by a task with higher
> > > priority and invoke hprobe_expire() somewhere else.
> >
> > This is clear, but ri_timer() still can not race with itself, no?
>
> No, ri_timer() can not race against itself.
Okay,
> The preempted ri_timer() could stall a read_seqcount_begin().
Again, nobody use read_seqcount_begin(utask->ri_seqcount).
free_ret_instance() uses raw_seqcount_try_begin(utask->ri_seqcount),
which, since ri_seqcount is seqcount_t, is just smp_load_acquire().
This can't stall.
Oleg.
next prev parent reply other threads:[~2025-04-02 12:19 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-04-01 21:04 uprobe splat in PREEMP_RT Alexei Starovoitov
2025-04-01 21:22 ` Steven Rostedt
2025-04-01 22:01 ` Andrii Nakryiko
2025-04-02 10:33 ` Oleg Nesterov
2025-04-02 10:57 ` Sebastian Sewior
2025-04-02 11:23 ` Oleg Nesterov
2025-04-02 12:13 ` Sebastian Sewior
2025-04-02 12:18 ` Oleg Nesterov [this message]
2025-04-02 12:24 ` Sebastian Sewior
2025-04-02 14:12 ` Oleg Nesterov
2025-04-03 7:37 ` Sebastian Sewior
2025-04-03 12:27 ` Oleg Nesterov
2025-04-03 16:04 ` Andrii Nakryiko
2025-04-02 16:15 ` Andrii Nakryiko
2025-04-02 16:57 ` Oleg Nesterov
2025-04-02 12:21 ` Sebastian Sewior
2025-04-02 9:10 ` Oleg Nesterov
2025-04-02 10:54 ` Sebastian Sewior
2025-04-02 11:20 ` Oleg Nesterov
2025-04-02 11:31 ` Oleg Nesterov
2025-04-02 12:06 ` Sebastian Sewior
2025-04-02 12:12 ` Oleg Nesterov
2025-04-02 12:16 ` Sebastian Sewior
2025-04-02 13:56 ` Oleg Nesterov
2025-04-02 14:23 ` Oleg Nesterov
2025-04-03 9:08 ` Sebastian Sewior
2025-04-03 12:11 ` Oleg Nesterov
2025-04-03 12:43 ` Oleg Nesterov
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