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From: Greg KH <gregkh@linuxfoundation.org>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
	Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
	arnd@arndb.de, linux-kernel@vger.kernel.org,
	linux-pm@vger.kernel.org,
	Wedson Almeida Filho <wedsonaf@google.com>
Subject: Re: [PATCH] char: misc: make misc_open() and misc_register() killable
Date: Tue, 5 Jul 2022 07:37:21 +0200	[thread overview]
Message-ID: <YsPOEYU7ZqmpD8dw@kroah.com> (raw)
In-Reply-To: <617f64e3-74c8-f98b-3430-bd476867e483@I-love.SAKURA.ne.jp>

On Tue, Jul 05, 2022 at 02:21:17PM +0900, Tetsuo Handa wrote:
> On 2022/07/04 23:31, Greg KH wrote:
> > I don't understand what you are trying to "fix" here.  What is userspace
> > doing (as a normal user) that is causing a problem, and what problem is
> > it causing and for what device/hardware/driver is this a problem?
> 
> Currently the root cause is unknown.
> This might be another example of deadlock hidden by device_initialize().
> 
> We can see from https://syzkaller.appspot.com/text?tag=CrashReport&x=11feb7e0080000 that
> when khungtaskd reports that a process is blocked waiting for misc_mtx at misc_open(),
> there is a process which is holding system_transition_mutex from snapshot_open().

/dev/snapshot is not read/writable by anyone but root for obvious
reasons.

And perhaps it's something that syzbot shouldn't be fuzzing unless it
wants to take the system down easily :)

thanks,

greg k-h

  reply	other threads:[~2022-07-05  5:37 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-13 12:38 INFO: task hung in misc_open (4) syzbot
2022-07-04  6:44 ` [PATCH] char: misc: make misc_open() and misc_register() killable Tetsuo Handa
2022-07-04  7:29   ` Greg KH
2022-07-04 10:25     ` Tetsuo Handa
2022-07-04 11:01       ` Greg KH
2022-07-04 12:34         ` Tetsuo Handa
2022-07-04 12:59           ` Wedson Almeida Filho
2022-07-04 13:48             ` Tetsuo Handa
2022-07-04 13:57               ` Wedson Almeida Filho
2022-07-04 14:07                 ` Tetsuo Handa
2022-07-04 14:46                   ` Wedson Almeida Filho
2022-07-04 14:31           ` Greg KH
2022-07-05  5:21             ` Tetsuo Handa
2022-07-05  5:37               ` Greg KH [this message]
     [not found]                 ` <a1fcc07e-51ef-eaad-f14b-33f1263e45ac@I-love.SAKURA.ne.jp>
2022-07-05  7:20                   ` Dmitry Vyukov
2022-07-05 10:10                     ` Greg Kroah-Hartman
2022-07-08  6:06                       ` Dmitry Vyukov
2022-07-05 14:01               ` Tetsuo Handa
2022-07-05 14:16                 ` Greg KH
2022-07-05 14:35                   ` Tetsuo Handa
2022-07-06  6:21                     ` Tetsuo Handa
2022-07-06  6:34                       ` Greg KH
2022-07-06 10:26                         ` Tetsuo Handa
2022-07-06 11:04                           ` Oliver Neukum
2022-07-07  5:06                             ` Tetsuo Handa
2022-07-07  8:04                               ` Greg KH
2022-07-08 13:37                               ` Greg KH
2022-07-10  2:27                                 ` Tetsuo Handa
2022-07-06 12:17                           ` Oliver Neukum

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