linux-kernel - Re: [Syzkaller] INFO: task hung in fuse

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Date:   Wed, 19 Oct 2022 10:53:38 +0800
From:   Pengfei Xu <pengfei.xu@...el.com>
To:     Miklos Szeredi <mszeredi@...hat.com>
CC:     <linux-kernel@...r.kernel.org>, <heng.su@...el.com>
Subject: Re: [Syzkaller] INFO: task hung in fuse_lookup with v6.0 kernel in
 guest

Hi Miklos,

On 2022-10-18 at 11:23:17 +0200, Miklos Szeredi wrote:
> On Mon, Oct 17, 2022 at 11:17 AM Pengfei Xu <pengfei.xu@...el.com> wrote:
> >
> > Hi Miklos,
> >
> > Greeting!
> >
> > Platform: Tiger lake CPU platform.
> >
> > We found 1 "task hung in fuse_lookup" issue by syzkaller with v6.0 mainline
> > kernel in guest.
> >
> > Bisected and found the bad commit:
> > "
> > commit:  62dd1fc8cc6b22e3e568be46ebdb817e66f5d6a5
> > fuse: move fget() to fuse_get_tree()
> > "
> >
> > Reproduced code generated by syzkaller, binary, bisect log and all the dmesg
> > info are in attached package.
> 
> Thanks for the report.
> 
> I tried out the reproducer, and the deadlock can be triggered.
> Unfortunately killing the deadlocked processes is not enough, but it
> still should be possible to recover with "echo 1 >
> /sys/fs/fuse/connections/$FUSE_DEV/abort".    In my tests this works,
> so I'm not sure there's anything to fix here.
  Thanks for the solution: "echo 1 >  /sys/fs/fuse/connections/$FUSE_DEV/abort"

> 
> Is there a real life situation where this occurs, or is this just
> triggered with fuzzing?
  It only could be reproduced by repro.c from syzkaller, and we have not
  encountered this problem in real life yet.
  So it's a low priority issue and it's not even clear if it's worth solving?

> 
> I'm wondering why syzbot didn't try aborting using the "abort" file in
> sysfs, AFAICS it does know this trick.
  Yes, maybe syzbot should improve it? :)

  Thanks!
  BR.

> 
> Thanks,
> Miklos
>