From: Roberto Sassu <roberto.sassu@huaweicloud.com>
To: Paul Moore <paul@paul-moore.com>,
syzbot <syzbot+8fb64a61fdd96b50f3b8@syzkaller.appspotmail.com>
Cc: hdanton@sina.com, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, reiserfs-devel@vger.kernel.org,
roberto.sassu@huawei.com, syzkaller-bugs@googlegroups.com,
peterz@infradead.org, mingo@redhat.com, will@kernel.org,
Jeff Mahoney <jeffm@suse.com>, Jan Kara <jack@suse.cz>
Subject: Re: [syzbot] [reiserfs?] possible deadlock in open_xa_dir
Date: Wed, 31 May 2023 11:52:06 +0200 [thread overview]
Message-ID: <38048f0a-7706-12c4-dc85-4d2fa13df015@huaweicloud.com> (raw)
In-Reply-To: <1020d006-c698-aacc-bcc3-92e5b237ef91@huaweicloud.com>
On 5/31/2023 11:49 AM, Roberto Sassu wrote:
> On 5/5/2023 11:36 PM, Paul Moore wrote:
>> On Fri, May 5, 2023 at 4:51 PM syzbot
>> <syzbot+8fb64a61fdd96b50f3b8@syzkaller.appspotmail.com> wrote:
>>>
>>> syzbot has bisected this issue to:
>>>
>>> commit d82dcd9e21b77d338dc4875f3d4111f0db314a7c
>>> Author: Roberto Sassu <roberto.sassu@huawei.com>
>>> Date: Fri Mar 31 12:32:18 2023 +0000
>>>
>>> reiserfs: Add security prefix to xattr name in
>>> reiserfs_security_write()
>>>
>>> bisection log:
>>> https://syzkaller.appspot.com/x/bisect.txt?x=14403182280000
>>> start commit: 3c4aa4434377 Merge tag 'ceph-for-6.4-rc1' of
>>> https://githu..
>>> git tree: upstream
>>> final oops:
>>> https://syzkaller.appspot.com/x/report.txt?x=16403182280000
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=12403182280000
>>> kernel config:
>>> https://syzkaller.appspot.com/x/.config?x=73a06f6ef2d5b492
>>> dashboard link:
>>> https://syzkaller.appspot.com/bug?extid=8fb64a61fdd96b50f3b8
>>> syz repro:
>>> https://syzkaller.appspot.com/x/repro.syz?x=12442414280000
>>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=176a7318280000
>>>
>>> Reported-by: syzbot+8fb64a61fdd96b50f3b8@syzkaller.appspotmail.com
>>> Fixes: d82dcd9e21b7 ("reiserfs: Add security prefix to xattr name in
>>> reiserfs_security_write()")
>>>
>>> For information about bisection process see:
>>> https://goo.gl/tpsmEJ#bisection
>>
>> I don't think Roberto's patch identified above is the actual root
>> cause of this problem as reiserfs_xattr_set_handle() is called in
>> reiserfs_security_write() both before and after the patch. However,
>> due to some bad logic in reiserfs_security_write() which Roberto
>> corrected, I'm thinking that it is possible this code is being
>> exercised for the first time and syzbot is starting to trigger a
>> locking issue in the reiserfs code ... ?
>
> + Jan, Jeff (which basically restructured the lock)
Actually adding Jan and Jeff.
Roberto
> + Petr, Ingo, Will
>
> I involve the lockdep experts, to get a bit of help on this.
>
> First of all, the lockdep warning is trivial to reproduce:
>
> # dd if=/dev/zero of=reiserfs.img bs=1M count=100
> # losetup -f --show reiserfs.img
> /dev/loop0
> # mkfs.reiserfs /dev/loop0
> # mount /dev/loop0 /mnt/
> # touch file0
>
> In the testing system, Smack is the major LSM.
>
> Ok, so the warning here is clear:
>
> https://syzkaller.appspot.com/x/log.txt?x=12403182280000
>
> However, I was looking if that can really happen. From this:
>
> [ 77.746561][ T5418] -> #1 (&sbi->lock){+.+.}-{3:3}:
> [ 77.753772][ T5418] lock_acquire+0x23e/0x630
> [ 77.758792][ T5418] __mutex_lock_common+0x1d8/0x2530
> [ 77.764504][ T5418] mutex_lock_nested+0x1b/0x20
> [ 77.769868][ T5418] reiserfs_write_lock+0x70/0xc0
> [ 77.775321][ T5418] reiserfs_mkdir+0x321/0x870
>
> I see that the lock is taken in reiserfs_write_lock(), while lockdep says:
>
> [ 77.710227][ T5418] but task is already holding lock:
> [ 77.717587][ T5418] ffff88807568d090 (&sbi->lock){+.+.}-{3:3}, at:
> reiserfs_write_lock_nested+0x4a/0xb0
>
> which is in a different place, I believe here:
>
> int reiserfs_paste_into_item(struct reiserfs_transaction_handle *th,
> /* Path to the pasted item. */
> [...]
>
> depth = reiserfs_write_unlock_nested(sb);
> dquot_free_space_nodirty(inode, pasted_size);
> reiserfs_write_lock_nested(sb, depth);
> return retval;
> }
>
> This is called by reiserfs_add_entry(), which is called by
> reiserfs_create() (it is in the lockdep trace). After returning to
> reiserfs_create(), d_instantiate_new() is called.
>
> I don't know exactly, I take the part that the lock is held. But if it
> is held, how d_instantiate_new() can be executed in another task?
>
> static int reiserfs_create(struct mnt_idmap *idmap, struct inode *dir,
> struct dentry *dentry, umode_t mode, bool excl)
> {
>
> [...]
>
> reiserfs_write_lock(dir->i_sb);
>
> retval = journal_begin(&th, dir->i_sb, jbegin_count);
>
> [...]
>
> d_instantiate_new(dentry, inode);
> retval = journal_end(&th);
>
> out_failed:
> reiserfs_write_unlock(dir->i_sb);
>
> If the lock is held, the scenario lockdep describes cannot happen. Any
> thoughts?
>
> Thanks
>
> Roberto
next prev parent reply other threads:[~2023-05-31 9:52 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-31 6:35 [syzbot] [reiserfs?] possible deadlock in open_xa_dir syzbot
2023-05-05 7:10 ` syzbot
2023-05-05 20:51 ` syzbot
2023-05-05 21:36 ` Paul Moore
2023-05-31 9:49 ` Roberto Sassu
2023-05-31 9:52 ` Roberto Sassu [this message]
2023-06-01 21:22 ` Jeff Mahoney
2023-06-02 7:20 ` Roberto Sassu
2023-06-02 8:56 ` Roberto Sassu
2023-06-02 9:17 ` syzbot
2023-06-02 16:18 ` Roberto Sassu
2023-06-02 16:39 ` syzbot
2023-06-02 16:46 ` Roberto Sassu
2023-06-01 20:19 ` Roberto Sassu
2023-06-01 20:38 ` syzbot
2023-06-01 20:30 ` Roberto Sassu
2023-06-01 20:57 ` syzbot
2024-03-09 22:20 ` syzbot
[not found] <20230505075628.4150-1-hdanton@sina.com>
2023-05-05 8:32 ` syzbot
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