Re: [syzbot] [jfs?] INFO: task hung in path_mount (2)

[Jens Axboe]

On 1/25/24 9:47 AM, Christian Brauner wrote:
> On Thu, Jan 25, 2024 at 09:11:34AM -0700, Jens Axboe wrote:
>> On Thu, Jan 25, 2024 at 9:08?AM Christian Brauner <brauner@xxxxxxxxxx> wrote:
>>>
>>> On Thu, Jan 25, 2024 at 03:59:03AM -0800, syzbot wrote:
>>>> syzbot suspects this issue was fixed by commit:
>>>>
>>>> commit 6f861765464f43a71462d52026fbddfc858239a5
>>>> Author: Jan Kara <jack@xxxxxxx>
>>>> Date:   Wed Nov 1 17:43:10 2023 +0000
>>>>
>>>>     fs: Block writes to mounted block devices
>>>>
>>>> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=13175a53e80000
>>>> start commit:   2ccdd1b13c59 Linux 6.5-rc6
>>>> git tree:       upstream
>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=9c37cc0e4fcc5f8d
>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=fb337a5ea8454f5f1e3f
>>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17ba5d53a80000
>>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14265373a80000
>>>>
>>>> If the result looks correct, please mark the issue as fixed by replying with:
>>>
>>> #syz fix: fs: Block writes to mounted block devices
>>
>> Like Dave replied a few days ago, I'm kind of skeptical on all of these
>> bugs being closed by this change. I'm guessing that they are all
>> resolved now because a) the block writes while mounted option was set to
>> Y, and b) the actual bug is just masked by that.
>>
>> Maybe this is fine, but it does seem a bit... sketchy? The bugs aren't
>> really fixed, and what happens if someone doesn't turn on that option?
>> If it's required, perhaps it should not be an option at all? Though
>> that'd seem to be likely to break some funky use cases, whether they are
>> valid or not.
> 
> We have no way of actually testing or verifying this stuff and a lot of
> these have been around for a long time. For example, this report here
> has a C reproducer but following the actual dashboard link that
> reproducer is striked-through which supposedly means that it isn't valid
> or reliable. And no other reproducer ever showed up.
> 
> As far as I can see we should just close reports such as. If this is a
> real bug that is separate from the ability to mount to writed block
> devices then one should hope that syzbot finds another reproducer that
> let's us really analyze the bug?
> 
> A separate issue is that syzbot keeps suggesting as all of these being
> closable because of this. So how serious can we take this and how much
> time can/should we spend given that we got ~20 or more of these mails in
> the last two weeks or so.
> 
> I have no better answers than this tbh. And fwiw, apart from this one I
> haven't closed a single bug based on this.

Oh yeah, it wasn't directed at you specifically, just the overall class
of bugs that get closed due to this in general.

> And yes, ideally the ability to write to mounted block devices should be
> turned off. But we'll have to let it trickle into the individual
> distributions first and make remaining userspace tools that rely on this
> move to alternate apis before we can make any serious effort.

Hopefully it's all fine on the distro front and we can just make it the
default some years from now. May even make sense to backport some of
this to stable and get it in their hands faster?

-- 
Jens Axboe