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From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	syzbot <syzbot+10007d66ca02b08f0e60@syzkaller.appspotmail.com>,
	dvyukov@google.com, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
	linux-block@vger.kernel.org
Subject: Re: INFO: task hung in __get_super
Date: Wed, 15 May 2019 20:32:27 +0900
Message-ID: <024bba2a-4d2f-1861-bfd9-819511bdf6eb@i-love.sakura.ne.jp> (raw)
In-Reply-To: <20190515102133.GA16193@quack2.suse.cz>

On 2019/05/15 19:21, Jan Kara wrote:
> The question is how to fix this problem. The simplest fix I can see is that
> we'd just refuse to do LOOP_SET_FD if someone has the block device
> exclusively open as there are high chances such user will be unpleasantly
> surprised by the device changing under him. OTOH this has some potential
> for userspace visible regressions. But I guess it's worth a try. Something
> like attached patch?

(1) If I understand correctly, FMODE_EXCL is set at blkdev_open() only if O_EXCL
    is specified. How can we detect if O_EXCL was not used, for the reproducer
    ( https://syzkaller.appspot.com/text?tag=ReproC&x=135385a8a00000 ) is not
    using O_EXCL ?

(2) There seems to be no serialization. What guarantees that mount_bdev()
    does not start due to preempted after the check added by this patch?

  reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <0000000000002cd22305879b22c4@google.com>
     [not found] ` <201905150102.x4F12b6o009249@www262.sakura.ne.jp>
2019-05-15 10:21   ` Jan Kara
2019-05-15 11:32     ` Tetsuo Handa [this message]
2019-05-15 13:07       ` Jan Kara
2019-05-16 11:48         ` Jan Kara
2019-05-16 12:17           ` Tetsuo Handa
2019-05-16 12:32             ` Jan Kara
2019-05-16 12:50               ` Tetsuo Handa
2019-05-16 12:33           ` syzbot
2019-05-15 11:59     ` syzbot

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