Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 31 May 2023 11:52:06 +0200 | Subject | Re: [syzbot] [reiserfs?] possible deadlock in open_xa_dir | From | Roberto Sassu <> |
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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
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