linux-kernel - Re: [syzbot] INFO: rcu detected stall in sys

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Date:   Wed, 20 Apr 2022 10:14:21 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     syzbot <syzbot+10a16d1c43580983f6a2@...kaller.appspotmail.com>,
        hdanton@...a.com
Cc:     fweisbec@...il.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        syzkaller-bugs@...glegroups.com, tglx@...utronix.de,
        viro@...iv.linux.org.uk
Subject: Re: [syzbot] INFO: rcu detected stall in sys_setxattr (2)

On Tue, Apr 19, 2022 at 09:16:20AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    b2d229d4ddb1 Linux 5.18-rc3
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=144417ccf00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=6cb89c879305f336
> dashboard link: https://syzkaller.appspot.com/bug?extid=10a16d1c43580983f6a2
> compiler:       Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=104a88e8f00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=132a840cf00000
> 
> The issue was bisected to:
> 
> commit e257039f0fc7da36ac3a522ef9a5cb4ae7852e67
> Author: Al Viro <viro@...iv.linux.org.uk>
> Date:   Tue Mar 1 04:04:20 2022 +0000
> 
>     mount_setattr(): clean the control flow and calling conventions
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=16b313c0f00000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=15b313c0f00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=11b313c0f00000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+10a16d1c43580983f6a2@...kaller.appspotmail.com
> Fixes: e257039f0fc7 ("mount_setattr(): clean the control flow and calling conventions")

This suspiciously looks like in the case of failing to make a single
read-write mount read-only we don't unset MNT_WRITE_HOLD in the new
error path that Al added.

Just saw that Hilf was testing a patch to this effect as well so putting
him on this thread.

Hilf, are you working on a fix for this I can pick up from you later or
should I come up with a patch?

Christian