From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: Oliver Neukum <oneukum@suse.com>, Sean Young <sean@mess.org>,
Alan Stern <stern@rowland.harvard.edu>,
Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Jarod Wilson <jarod@redhat.com>,
syzbot <syzbot+c558267ad910fc494497@syzkaller.appspotmail.com>,
andreyknvl@google.com, linux-media@vger.kernel.org,
linux-usb@vger.kernel.org, syzkaller-bugs@googlegroups.com
Subject: Re: [PATCH v2 (resend)] media: imon: reorganize serialization
Date: Mon, 2 May 2022 20:05:15 +0900 [thread overview]
Message-ID: <1b7b9a2a-d52c-ff35-f32d-d22d7980a80f@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <6ab13405-b942-ddbe-c2de-dd193fe40795@suse.com>
On 2022/05/02 19:46, Oliver Neukum wrote:
>
>
> On 02.05.22 05:49, Tetsuo Handa wrote:
> Hi,
>
> there is one open question with this patch I am afraid.
>>
>> @@ -533,8 +550,10 @@ static int display_open(struct inode *inode, struct file *file)
>>
>> mutex_unlock(&ictx->lock);
>>
>> + if (retval && refcount_dec_and_test(&ictx->users))
>> + free_imon_context(ictx);
>> +
>>
>
> When could this ever happen? Either the device is disconnected, then
> you'll go to 'exit' or the refcount will go back to something >0, won't it?
>
(Step 0) Say, ictx->users is initially 1.
(Step 1) display_open() increments via refcount_inc_not_zero(), now is 2.
(Step 2) imon_disconnect() decrements via refcount_dec_and_test(), now is 1.
(Step 3) if retval != 0, display_open() needs to undo (Step 1) via
refcount_dec_and_test(), now is 0.
because imon_disconnect() can be called while display_open() is in progress...
next prev parent reply other threads:[~2022-05-02 11:08 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-09 13:18 possible deadlock in display_open syzbot
2022-04-25 5:29 ` Tetsuo Handa
2022-04-25 9:20 ` Sean Young
2022-04-25 11:14 ` Tetsuo Handa
2022-04-25 11:56 ` Sean Young
2022-04-25 16:01 ` Alan Stern
2022-04-25 16:21 ` Sean Young
2022-04-26 0:54 ` [PATCH] media: imon: remove redundant serialization Tetsuo Handa
2022-04-26 7:57 ` Sean Young
2022-04-26 10:32 ` [PATCH v2] media: imon: reorganize serialization Tetsuo Handa
2022-05-02 3:49 ` [PATCH v2 (resend)] " Tetsuo Handa
2022-05-02 9:39 ` Sean Young
2022-05-02 10:26 ` Tetsuo Handa
2022-05-02 10:40 ` Tetsuo Handa
2022-05-02 10:46 ` Oliver Neukum
2022-05-02 11:05 ` Tetsuo Handa [this message]
2022-05-03 7:41 ` Oliver Neukum
2022-05-02 12:53 ` Greg KH
2022-05-02 13:04 ` Tetsuo Handa
2022-05-02 13:06 ` Greg KH
2022-05-02 13:40 ` Tetsuo Handa
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