linux-kernel - Re: [syzbot] [btrfs?] possible deadlock in join

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Date: Wed, 15 May 2024 17:27:47 +0200
From: David Sterba <dsterba@...e.cz>
To: syzbot <syzbot+f7a41568dd5872d6ad52@...kaller.appspotmail.com>
Cc: clm@...com, dsterba@...e.com, josef@...icpanda.com,
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [btrfs?] possible deadlock in join_transaction

On Sat, May 11, 2024 at 04:23:20PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    dccb07f2914c Merge tag 'for-6.9-rc7-tag' of git://git.kern..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17ad432f180000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a450595960709c8
> dashboard link: https://syzkaller.appspot.com/bug?extid=f7a41568dd5872d6ad52
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> userspace arch: i386
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7bc7510fe41f/non_bootable_disk-dccb07f2.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/987455e5cf13/vmlinux-dccb07f2.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/327c390f753b/bzImage-dccb07f2.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+f7a41568dd5872d6ad52@...kaller.appspotmail.com
> 
> ======================================================
> WARNING: possible circular locking dependency detected
> 6.9.0-rc7-syzkaller-00012-gdccb07f2914c #0 Not tainted
> ------------------------------------------------------
> kswapd0/110 is trying to acquire lock:
> ffff888000c76380 (btrfs_trans_num_writers){++++}-{0:0}, at: join_transaction+0x430/0xf40 fs/btrfs/transaction.c:290
> 
> but task is already holding lock:
> ffff88805a236610 (sb_internal#2){.+.+}-{0:0}, at: btrfs_commit_inode_delayed_inode+0x110/0x330 fs/btrfs/delayed-inode.c:1275
> 
> which lock already depends on the new lock.

Looks valid, though I haven't went through all the traces, there are
some usual suspects like shrinkers, evict, iput, and in two threads (#4 and #0).

Also this is on 6.9, so the recent addition of shrinker for extent_map
is not relevant here.