From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@infradead.org>,
Dave Chinner <dchinner@redhat.com>,
linux-block@vger.kernel.org, Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH] loop: make autoclear operation asynchronous
Date: Thu, 2 Dec 2021 23:39:42 +0900 [thread overview]
Message-ID: <3f4d1916-8e70-8914-57ba-7291f40765ae@i-love.sakura.ne.jp> (raw)
In-Reply-To: <20211202121615.GC1815@quack2.suse.cz>
On 2021/12/02 21:16, Jan Kara wrote:
> Why not scheduling this using task_work_add()? It solves the locking
> context problems, has generally lower overhead than normal work (no need to
> schedule), and avoids possible unexpected side-effects of releasing
> loopback device later. Also task work is specifically designed so that one
> task work can queue another task work so we should be fine using it.
Indeed. But that will make really no difference between synchronous approach
( https://lkml.kernel.org/r/fb6adcdc-fb56-3b90-355b-3f5a81220f2b@i-love.sakura.ne.jp )
and asynchronous approach
( https://lkml.kernel.org/r/d1f760f9-cdb2-f40d-33d8-bfa517c731be@i-love.sakura.ne.jp ), for
disk->open_mutex is the only lock held when lo_release() is called.
Both approaches allow __loop_clr_fd() to run with no lock held, and both approaches
need to be aware of what actions are taken by blkdev_put() before and after dropping
disk->open_mutex. And bdev->bd_disk->fops->release() is the last action taken before
dropping disk->open_mutex.
What is so happier with preventing what will be done after disk->open_mutex is dropped
by blkdev_put() (i.e. __module_get() + kobject_get() before blkdev_put() calls
kobject_put() + module_put(), and kobject_put() + module_put() upon task_work_run()),
compared to doing things that can be done without disk->open_mutex (i.e. calling
__loop_clr_fd() without disk->open_mutex) ?
next prev parent reply other threads:[~2021-12-02 14:40 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-27 7:10 [syzbot] possible deadlock in blkdev_put (2) syzbot
2021-11-27 11:27 ` Tetsuo Handa
2021-11-28 5:32 ` Tetsuo Handa
2021-11-28 7:42 ` Tetsuo Handa
2021-11-29 10:21 ` Christoph Hellwig
2021-11-29 10:36 ` Tetsuo Handa
2021-11-29 14:13 ` Tetsuo Handa
2021-11-30 12:57 ` Christoph Hellwig
2021-12-01 14:41 ` [PATCH] loop: make autoclear operation asynchronous Tetsuo Handa
2021-12-02 7:22 ` Christoph Hellwig
2021-12-02 11:03 ` Tetsuo Handa
2021-12-02 12:16 ` Jan Kara
2021-12-02 14:39 ` Tetsuo Handa [this message]
2021-12-02 18:05 ` Jan Kara
2021-12-03 6:50 ` Christoph Hellwig
2021-12-03 11:01 ` Tetsuo Handa
2021-12-08 9:56 ` Tetsuo Handa
2021-12-08 5:05 ` [syzbot] possible deadlock in blkdev_put (2) syzbot
2021-12-08 11:42 ` syzbot
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