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AJvYcCVyNGx5xDcsGaNxJJsV9wyGrONA4+iV9E8lWnA1KGOD87822XbcN+42ufVLLGMlnd/hWst2MJ9c9/KiOaVP2jXRfhzQAapRfUR0/UGV X-Gm-Message-State: AOJu0YzZP6DaTZRJUlvh4Ra4All92siGITg4HkIpGWZDZLFrvm9RCIHn 2BwwFa+RSPJ8B//7aXpfir/KF0AKv/PNijMnrEEt0VE/hcE+k6Xn X-Google-Smtp-Source: AGHT+IFGpZR2YtZobflHmofogwGIAmCHG0go1fqlzmSQEcoFqmffLFqMWjBXdMl1Taf3eaT4uezs8A== X-Received: by 2002:a17:906:228d:b0:a77:c314:d621 with SMTP id a640c23a62f3a-a77c314d83amr592775266b.13.1720453201110; Mon, 08 Jul 2024 08:40:01 -0700 (PDT) Received: from [192.168.42.229] ([85.255.235.223]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a780a7ff021sm4139166b.103.2024.07.08.08.40.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 08 Jul 2024 08:40:00 -0700 (PDT) Message-ID: <62c11b59-c909-4c60-8370-77729544ec0a@gmail.com> Date: Mon, 8 Jul 2024 16:40:07 +0100 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] kernel: rerun task_work while freezing in get_signal() To: Oleg Nesterov Cc: io-uring@vger.kernel.org, Jens Axboe , Andrew Morton , Christian Brauner , Tycho Andersen , Thomas Gleixner , linux-kernel@vger.kernel.org, Julian Orth , Tejun Heo , Peter Zijlstra References: <1d935e9d87fd8672ef3e8a9a0db340d355ea08b4.1720368770.git.asml.silence@gmail.com> <20240708104221.GA18761@redhat.com> Content-Language: en-US From: Pavel Begunkov In-Reply-To: <20240708104221.GA18761@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 7/8/24 11:42, Oleg Nesterov wrote: > On 07/07, Pavel Begunkov wrote: >> >> io_uring can asynchronously add a task_work while the task is getting >> freezed. TIF_NOTIFY_SIGNAL will prevent the task from sleeping in >> do_freezer_trap(), and since the get_signal()'s relock loop doesn't >> retry task_work, the task will spin there not being able to sleep >> until the freezing is cancelled / the task is killed / etc. >> >> Cc: stable@vger.kernel.org >> Link: https://github.com/systemd/systemd/issues/33626 >> Fixes: 3146cba99aa28 ("io-wq: make worker creation resilient against signals") > > I don't think we should blame io_uring even if so far it is the only user > of TWA_SIGNAL. And it's not entirely correct even for backporting purposes, I'll pin it to when freezing was introduced then. > Perhaps we should change do_freezer_trap() somehow, not sure... It assumes > that TIF_SIGPENDING is the only reason to not sleep in TASK_INTERRUPTIBLE, > today this is not true. Let's CC Peter Zijlstra and Tejun in case they might have some input on that. Link to this patch for convenience: https://lore.kernel.org/all/1d935e9d87fd8672ef3e8a9a0db340d355ea08b4.1720368770.git.asml.silence@gmail.com/ >> --- a/kernel/signal.c >> +++ b/kernel/signal.c >> @@ -2694,6 +2694,10 @@ bool get_signal(struct ksignal *ksig) >> try_to_freeze(); >> >> relock: >> + clear_notify_signal(); >> + if (unlikely(task_work_pending(current))) >> + task_work_run(); >> + >> spin_lock_irq(&sighand->siglock); > > Well, but can't we kill the same code at the start of get_signal() then? > Of course, in this case get_signal() should check signal_pending(), not > task_sigpending(). Should be fine, but I didn't want to change the try_to_freeze() -> __refrigerator() path, which also reschedules. > Or perhaps something like the patch below makes more sense? I dunno... It needs a far backporting, I'd really prefer to keep it lean and without more side effects if possible, unless there is a strong opinion on that. > Oleg. > > diff --git a/kernel/signal.c b/kernel/signal.c > index 1f9dd41c04be..e2ae85293fbb 100644 > --- a/kernel/signal.c > +++ b/kernel/signal.c > @@ -2676,6 +2676,7 @@ bool get_signal(struct ksignal *ksig) > struct signal_struct *signal = current->signal; > int signr; > > +start: > clear_notify_signal(); > if (unlikely(task_work_pending(current))) > task_work_run(); > @@ -2760,10 +2761,11 @@ bool get_signal(struct ksignal *ksig) > if (current->jobctl & JOBCTL_TRAP_MASK) { > do_jobctl_trap(); > spin_unlock_irq(&sighand->siglock); > + goto relock; > } else if (current->jobctl & JOBCTL_TRAP_FREEZE) > do_freezer_trap(); > - > - goto relock; > + goto start; > + } > } > > /* > -- Pavel Begunkov