linux-kernel - Re: [syzbot] [fs?] KCSAN: data-race in choose_mountpoint_rcu / umount

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Message-ID: <20250422-flogen-firmieren-105a92fbd796@brauner>
Date: Tue, 22 Apr 2025 15:43:21 +0200
From: Christian Brauner <brauner@...nel.org>
To: syzbot <syzbot+81fdaf0f522d5c5e41fb@...kaller.appspotmail.com>
Cc: jack@...e.cz, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk
Subject: Re: [syzbot] [fs?] KCSAN: data-race in choose_mountpoint_rcu /
 umount_tree

On Tue, Apr 22, 2025 at 05:11:27AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    a33b5a08cbbd Merge tag 'sched_ext-for-6.15-rc3-fixes' of g..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1058f26f980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=85dd0f8b81b9d41f
> dashboard link: https://syzkaller.appspot.com/bug?extid=81fdaf0f522d5c5e41fb
> compiler:       Debian clang version 15.0.6, Debian LLD 15.0.6
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/718e6f7bde0a/disk-a33b5a08.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/20f5e402fb15/vmlinux-a33b5a08.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/2dd06e277fc7/bzImage-a33b5a08.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+81fdaf0f522d5c5e41fb@...kaller.appspotmail.com
> 
> ==================================================================
> BUG: KCSAN: data-race in choose_mountpoint_rcu / umount_tree

Benign, as this would be detected by the changed sequence count of
@mount_lock. I hope we won't end up with endless reports about:w
anything that we protect with a seqlock. That'll be very annoying.