linux-kernel - Re: [PATCH v2] exec: make de

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Date:   Mon, 12 Nov 2018 10:51:21 +0100
From:   Pavel Machek <pavel@....cz>
To:     Chanho Min <chanho.min@....com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Christian Brauner <christian@...uner.io>,
        Oleg Nesterov <oleg@...hat.com>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        Seungho Park <seungho1.park@....com>,
        Inkyu Hwang <inkyu.hwang@....com>,
        Donghwan Jung <donghwan.jung@....com>,
        Jongsung Kim <neidhard.kim@....com>
Subject: Re: [PATCH v2] exec: make de_thread() freezable

On Mon 2018-11-12 12:54:45, Chanho Min wrote:
> Suspend fails due to the exec family of functions blocking the freezer.
> The casue is that de_thread() sleeps in TASK_UNINTERRUPTIBLE waiting for
> all sub-threads to die, and we have the deadlock if one of them is frozen.
> This also can occur with the schedule() waiting for the group thread leader
> to exit if it is frozen.
> 
> In our machine, it causes freeze timeout as bellows.
> 
> Freezing of tasks failed after 20.010 seconds (1 tasks refusing to freeze, wq_busy=0):
> setcpushares-ls D ffffffc00008ed70     0  5817   1483 0x0040000d
>  Call trace:
> [<ffffffc00008ed70>] __switch_to+0x88/0xa0
> [<ffffffc000d1c30c>] __schedule+0x1bc/0x720
> [<ffffffc000d1ca90>] schedule+0x40/0xa8
> [<ffffffc0001cd784>] flush_old_exec+0xdc/0x640
> [<ffffffc000220360>] load_elf_binary+0x2a8/0x1090
> [<ffffffc0001ccff4>] search_binary_handler+0x9c/0x240
> [<ffffffc00021c584>] load_script+0x20c/0x228
> [<ffffffc0001ccff4>] search_binary_handler+0x9c/0x240
> [<ffffffc0001ce8e0>] do_execveat_common.isra.14+0x4f8/0x6e8
> [<ffffffc0001cedd0>] compat_SyS_execve+0x38/0x48
> [<ffffffc00008de30>] el0_svc_naked+0x24/0x28
> 
> To fix this, make de_thread() freezable. It looks safe and works fine.
> 
> Changes in v2:
>  - changes for the same reason in "if (!thread_group_leader(tsk))" branch.
>    (reported by Oleg)
> 
> Suggested-by: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Chanho Min <chanho.min@....com>

Acked-by: Pavel Machek <pavel@....cz>


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