[syzbot] [btrfs?] WARNING in btrfs_use_block_rsv

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3b35375f19fe Merge tag 'irq-urgent-2023-08-26' of git://gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1156791fa80000
kernel config: https://syzkaller.appspot.com/x/.config?x=67db137b0441ab96
dashboard link: https://syzkaller.appspot.com/bug?extid=10d5b62a8d7046b86d22
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1767c1e0680000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=146903b0680000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7bc7510fe41f/non_bootable_disk-3b35375f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/34c4f640b690/vmlinux-3b35375f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/58c9c2459f41/bzImage-3b35375f.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/501d7ead33fe/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+10d5b6...@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: CPU: 1 PID: 5212 at fs/btrfs/block-rsv.c:515 btrfs_use_block_rsv+0x688/0x7f0 fs/btrfs/block-rsv.c:515
Modules linked in:
CPU: 1 PID: 5212 Comm: kworker/u17:1 Not tainted 6.5.0-rc7-syzkaller-00182-g3b35375f19fe #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Workqueue: btrfs-endio-write btrfs_work_helper
RIP: 0010:btrfs_use_block_rsv+0x688/0x7f0 fs/btrfs/block-rsv.c:515
Code: 89 ea 83 e2 07 38 d0 7f 0c 84 c0 74 08 48 89 ef e8 ed 42 47 fe 0f b6 73 5a ba e4 ff ff ff 48 c7 c7 00 e4 b7 8a e8 b8 b8 ba fd <0f> 0b e9 a3 fd ff ff e8 8c f7 f3 fd 49 8d 9d 80 04 00 00 e9 1c fb
RSP: 0018:ffffc90003737030 EFLAGS: 00010282
RAX: 0000000000000000 RBX: ffff8880323ba608 RCX: 0000000000000000
RDX: ffff888029a1c4c0 RSI: ffffffff814be3c6 RDI: 0000000000000001
RBP: ffff8880323ba662 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 000000002d2d2d2d R12: 0000000000001000
R13: ffff88801fb84000 R14: 0000000000000001 R15: 0000000000000001
FS: 0000000000000000(0000) GS:ffff88806b700000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020d41000 CR3: 00000000219e2000 CR4: 0000000000350ee0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
btrfs_alloc_tree_block+0x1dd/0x1420 fs/btrfs/extent-tree.c:4883
__btrfs_cow_block+0x3ce/0x18e0 fs/btrfs/ctree.c:546
btrfs_cow_block+0x2f1/0x820 fs/btrfs/ctree.c:712
btrfs_search_slot+0x12a0/0x30e0 fs/btrfs/ctree.c:2194
btrfs_lookup_file_extent+0xcb/0x110 fs/btrfs/file-item.c:270
btrfs_drop_extents+0x433/0x2bd0 fs/btrfs/file.c:250
insert_reserved_file_extent+0x3a8/0x940 fs/btrfs/inode.c:3057
insert_ordered_extent_file_extent fs/btrfs/inode.c:3164 [inline]
btrfs_finish_one_ordered+0x1443/0x2240 fs/btrfs/inode.c:3268
btrfs_work_helper+0x20b/0xba0 fs/btrfs/async-thread.c:314
process_one_work+0xaa2/0x16f0 kernel/workqueue.c:2600
worker_thread+0x687/0x1110 kernel/workqueue.c:2751
kthread+0x33a/0x430 kernel/kthread.c:389
ret_from_fork+0x2c/0x70 arch/x86/kernel/process.c:145
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:304
</TASK>


---
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[syzbot]

syzbot has bisected this issue to:

commit a5b8a5f9f8355d27a4f8d0afa93427f16d2f3c1e
Author: Anand Jain <anand...@oracle.com>
Date: Thu Sep 28 01:09:47 2023 +0000

btrfs: support cloned-device mount capability

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1446d344e80000
start commit: d3fa86b1a7b4 Merge tag 'net-6.7-rc3' of git://git.kernel.o..
git tree: upstream
final oops: https://syzkaller.appspot.com/x/report.txt?x=1646d344e80000
console output: https://syzkaller.appspot.com/x/log.txt?x=1246d344e80000
kernel config: https://syzkaller.appspot.com/x/.config?x=6ae1a4ee971a7305
dashboard link: https://syzkaller.appspot.com/bug?extid=10d5b62a8d7046b86d22
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1431040ce80000

Reported-by: syzbot+10d5b6...@syzkaller.appspotmail.com
Fixes: a5b8a5f9f835 ("btrfs: support cloned-device mount capability")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

[Anand Jain]

It is completely strange that this issue bisects to the commit
a5b8a5f9f835 ('btrfs: support cloned-device mount capability').
I am unable to reproduce this as well.

-------------------
WARNING: CPU: 1 PID: 58 at fs/btrfs/block-rsv.c:523
btrfs_use_block_rsv+0x60d/0x860 fs/btrfs/block-rsv.c:523
<snap>
Call Trace:
<TASK>
btrfs_alloc_tree_block+0x1e0/0x12c0 fs/btrfs/extent-tree.c:5114
btrfs_force_cow_block+0x3e5/0x19e0 fs/btrfs/ctree.c:563
btrfs_cow_block+0x2b6/0xb30 fs/btrfs/ctree.c:741
push_leaf_left+0x315/0x4d0 fs/btrfs/ctree.c:3485
split_leaf+0x9c3/0x13b0 fs/btrfs/ctree.c:3681
search_leaf fs/btrfs/ctree.c:1944 [inline]
btrfs_search_slot+0x24ba/0x2fd0 fs/btrfs/ctree.c:2131
btrfs_insert_empty_items+0xb6/0x1b0 fs/btrfs/ctree.c:4285
btrfs_insert_empty_item fs/btrfs/ctree.h:657 [inline]
insert_reserved_file_extent+0x7aa/0x950 fs/btrfs/inode.c:2907
insert_ordered_extent_file_extent fs/btrfs/inode.c:3005 [inline]
btrfs_finish_one_ordered+0x12dc/0x20d0 fs/btrfs/inode.c:3113
btrfs_work_helper+0x210/0xbf0 fs/btrfs/async-thread.c:315
process_one_work+0x886/0x15d0 kernel/workqueue.c:2630
process_scheduled_works kernel/workqueue.c:2703 [inline]
worker_thread+0x8b9/0x1290 kernel/workqueue.c:2784
kthread+0x2c6/0x3a0 kernel/kthread.c:388
ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
-----------------

btrfs_use_block_rsv()
<snap>
/*
* The global reserve still exists to save us from ourselves,
so don't
* warn_on if we are short on our delayed refs reserve.
*/
if (block_rsv->type != BTRFS_BLOCK_RSV_DELREFS &&
btrfs_test_opt(fs_info, ENOSPC_DEBUG)) {
static DEFINE_RATELIMIT_STATE(_rs,
DEFAULT_RATELIMIT_INTERVAL * 10,
/*DEFAULT_RATELIMIT_BURST*/ 1);
if (__ratelimit(&_rs))
WARN(1, KERN_DEBUG
"BTRFS: block rsv %d returned %d\n",
block_rsv->type, ret);
}
----------



Thanks, Anand

[David Sterba]

On Sun, Nov 26, 2023 at 06:59:41AM +0800, Anand Jain wrote:
>
>
> On 25/11/2023 10:08, syzbot wrote:
> > syzbot has bisected this issue to:
> >
> > commit a5b8a5f9f8355d27a4f8d0afa93427f16d2f3c1e
> > Author: Anand Jain <anand...@oracle.com>
> > Date: Thu Sep 28 01:09:47 2023 +0000
> >
> > btrfs: support cloned-device mount capability
> >
> > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1446d344e80000
> > start commit: d3fa86b1a7b4 Merge tag 'net-6.7-rc3' of git://git.kernel.o..
> > git tree: upstream
> > final oops: https://syzkaller.appspot.com/x/report.txt?x=1646d344e80000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1246d344e80000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=6ae1a4ee971a7305
> > dashboard link: https://syzkaller.appspot.com/bug?extid=10d5b62a8d7046b86d22
> > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1431040ce80000
> >
> > Reported-by: syzbot+10d5b6...@syzkaller.appspotmail.com
> > Fixes: a5b8a5f9f835 ("btrfs: support cloned-device mount capability")
> >
> > For information about bisection process see: https://goo.gl/tpsmEJ#bisection
>
>
> It is completely strange that this issue bisects to the commit
> a5b8a5f9f835 ('btrfs: support cloned-device mount capability').
> I am unable to reproduce this as well.

I think it's because of changed timing or it can be an inconclusive
bisect. Things around space handling depend on timing, the test would
need to be run a few times to be sure.

The report provides an image so it may be good to analyze if it's scaled
properly or if the reproducer does something strange.

[Aleksandr Nogikh]

Bisection log itself looks reasonable.

One other case to consider is that "btrfs: support cloned-device mount
capability" just helped surface the problem. Syzbot can only bisect
for the revision at which the reproducer started/stopped working and,
even though we try to minimize the reproducer (*), it may still rely
on some functionality that's not related to the actual bug. One of the
possibilities here is that the slightly changed validation rules in
btrfs_validate_super() allowed syzkaller to trigger a problem
somewhere else.

(*) We don't do it for filesystem images themselves as it does not
make very much sense -- in almost all cases by zeroing/dropping bytes
syzkaller just breaks the image and the reproducer stops working.
Without knowing the underlying fs image structure in detail it just
doesn't work as intended.

--
Aleksandr

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