From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
Oleg Nesterov <oleg@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Andy Lutomirski <luto@kernel.org>,
Ben Segall <bsegall@google.com>, Borislav Petkov <bp@alien8.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>, Mel Gorman <mgorman@suse.de>,
Peter Zijlstra <peterz@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
Vincent Guittot <vincent.guittot@linaro.org>
Subject: Re: [PATCH] signal/x86: Delay calling signals in atomic
Date: Mon, 28 Mar 2022 18:17:38 +0200 [thread overview]
Message-ID: <YkHfokLO1UGCISGc@linutronix.de> (raw)
In-Reply-To: <8735j2xigt.fsf@email.froward.int.ebiederm.org>
On 2022-03-28 09:25:06 [-0500], Eric W. Biederman wrote:
> Sebastian Andrzej Siewior <bigeasy@linutronix.de> writes:
>
> Folks I really would have appreciated being copied on a signal handling
> patch like this.
Sorry for that. For the whole ptrace/signal part is no maintainer listed
and I got the feeling that Oleg knows these bits.
> It is too late to nack, but I think this buggy patch deserved one. Can
> we please fix PREEMPT_RT instead?
Sure.
> As far as I can tell this violates all of rules from
> implementing/maintaining the RT kernel. Instead of coming up with new
> abstractions that makes sense and can use by everyone this introduces
> a hack only for PREEMPT_RT and a pretty horrible one at that.
>
> This talks about int3, but the code looks for in_atomic(). Which means
> that essentially every call of force_sig will take this path as they
> almost all come from exception handlers. It is the nature of signals
> that report on faults. An exception is raised and the kernel reports it
> to userspace with a fault signal (aka force_sig_xxx).
The int3 is invoked with disabled interrupts. There are also a few
others path which are explicit with disabled interrupts or with a
raw_spinlock_t which lead to an atomic section on PREEMPT_RT. Call
chains with spinlock_t or a rwlock_t don't lead to a atomic section on
PREEMPT_RT. Therefore I don't think this is "essentially every call of
force_sig" that is going to use that.
> Further this code is buggy. TIF_NOTIFY_RESUME is not the correct
> flag to set to enter into exit_to_usermode_loop. TIF_NOTIFY_RESUME is
> about that happens after signal handling. This very much needs to be
> TIF_SIGPENDING with recalc_sigpending and friends updated to know about
> "task->force_info".
>
> Does someone own this problem? Can that person please fix this
> properly?
Sure. Instead setting TIF_NOTIFY_RESUME you want the code updated to use
recalc_sigpending() only. Or do you have other suggestions regarding
fixing this properly?
> I really don't think it is going to be maintainable for PREEMPT_RT to
> maintain a separate signal delivery path for faults from the rest of
> linux.
Okay.
> Eric
Sebastian
next prev parent reply other threads:[~2022-03-28 16:17 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-14 20:19 [PATCH] signal/x86: Delay calling signals in atomic Sebastian Andrzej Siewior
2022-03-28 14:25 ` Eric W. Biederman
2022-03-28 14:41 ` Eric W. Biederman
2022-03-28 16:32 ` Sebastian Andrzej Siewior
2022-03-28 14:48 ` Eric W. Biederman
2022-03-28 16:17 ` Sebastian Andrzej Siewior [this message]
2022-03-28 22:07 ` Eric W. Biederman
2022-03-29 9:31 ` Sebastian Andrzej Siewior
2022-03-30 18:10 ` Eric W. Biederman
2022-04-01 11:45 ` Sebastian Andrzej Siewior
2022-04-04 14:29 ` Eric W. Biederman
2022-03-28 16:28 ` Thomas Gleixner
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