[syzbot] [nilfs?] kernel BUG in end_buffer_async_write

[syzbot] [nilfs?] kernel BUG in end_buffer_async_write

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    51f269a6ecc7 Merge tag 'probes-fixes-6.4-rc4' of git://git..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15ed0e7d280000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3da6c5d3e0a6c932
dashboard link: https://syzkaller.appspot.com/bug?extid=5c04210f7c7f897c1e7f
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1336c6b5280000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12c0a5a5280000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/8a8c8e41a6b0/disk-51f269a6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ffc3737b4233/vmlinux-51f269a6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d49888e5beb1/bzImage-51f269a6.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/99d35f050c12/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5c04210f7c7f897c1e7f-Pl5Pbv+GP7P466ipTTIvnc23WoclnBCfAL8bYrjMMd8@public.gmane.org

------------[ cut here ]------------
kernel BUG at fs/buffer.c:391!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 15 Comm: ksoftirqd/0 Not tainted 6.4.0-rc4-syzkaller-00268-g51f269a6ecc7 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/25/2023
RIP: 0010:end_buffer_async_write+0x2db/0x340 fs/buffer.c:391
Code: 65 00 fe 4c 89 ff e8 d4 a3 ff ff be 08 00 00 00 48 89 c7 48 89 c3 e8 b4 31 e0 ff f0 80 4b 01 01 e9 07 fe ff ff e8 45 62 8d ff <0f> 0b e8 3e 62 8d ff 0f 0b 48 89 df e8 34 2b e0 ff e9 d9 fe ff ff
RSP: 0018:ffffc90000147c98 EFLAGS: 00010246

RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000100
RDX: ffff88801664bb80 RSI: ffffffff81f6e3fb RDI: 0000000000000001
RBP: ffff88806fbde570 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
R13: ffffffff81f6e120 R14: ffff88801e24ee00 R15: ffff88802a45a788
FS:  0000000000000000(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f42b45b0000 CR3: 000000007b04a000 CR4: 0000000000350ef0
Call Trace:
 <TASK>
 end_bio_bh_io_sync+0xde/0x130 fs/buffer.c:2730
 bio_endio+0x5af/0x6c0 block/bio.c:1608
 req_bio_endio block/blk-mq.c:761 [inline]
 blk_update_request+0x5c5/0x1620 block/blk-mq.c:906
 blk_mq_end_request+0x59/0x4c0 block/blk-mq.c:1023
 lo_complete_rq+0x1c6/0x280 drivers/block/loop.c:370
 blk_complete_reqs+0xad/0xe0 block/blk-mq.c:1101
 __do_softirq+0x1d4/0x905 kernel/softirq.c:571
 run_ksoftirqd kernel/softirq.c:939 [inline]
 run_ksoftirqd+0x31/0x60 kernel/softirq.c:931
 smpboot_thread_fn+0x659/0x9e0 kernel/smpboot.c:164
 kthread+0x344/0x440 kernel/kthread.c:379
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:end_buffer_async_write+0x2db/0x340 fs/buffer.c:391
Code: 65 00 fe 4c 89 ff e8 d4 a3 ff ff be 08 00 00 00 48 89 c7 48 89 c3 e8 b4 31 e0 ff f0 80 4b 01 01 e9 07 fe ff ff e8 45 62 8d ff <0f> 0b e8 3e 62 8d ff 0f 0b 48 89 df e8 34 2b e0 ff e9 d9 fe ff ff
RSP: 0018:ffffc90000147c98 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000100
RDX: ffff88801664bb80 RSI: ffffffff81f6e3fb RDI: 0000000000000001
RBP: ffff88806fbde570 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
R13: ffffffff81f6e120 R14: ffff88801e24ee00 R15: ffff88802a45a788
FS:  0000000000000000(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f42b45b0000 CR3: 000000007b04a000 CR4: 0000000000350ef0


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the bug is already fixed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to change bug's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the bug is a duplicate of another bug, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[PATCH] nilfs2: fix potential bug in end_buffer_async_write

[Ryusuke Konishi]

According to a syzbot report, end_buffer_async_write(), which handles
the completion of block device writes, may detect abnormal condition
of the buffer async_write flag and cause a BUG_ON failure when using
nilfs2.

Nilfs2 itself does not use end_buffer_async_write().
But, the async_write flag is now used as a marker by
commit 7f42ec394156 ("nilfs2: fix issue with race condition of
competition between segments for dirty blocks") as a means of
resolving double list insertion of dirty blocks in
nilfs_lookup_dirty_data_buffers() and nilfs_lookup_node_buffers()
and the resulting crash.

This modification is safe as long as it is used for file data and
b-tree node blocks where the page caches are independent.  However,
it was irrelevant and redundant to also introduce async_write for
segment summary and super root blocks that share buffers with the
backing device.  This led to the possibility that the BUG_ON check
in end_buffer_async_write would fail as described above, if
independent writebacks of the backing device occurred in parallel.

The use of async_write for segment summary buffers has already been
removed in a previous change.

Fix this issue by removing the manipulation of the async_write flag
for the remaining super root block buffer.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Reported-by: syzbot+5c04210f7c7f897c1e7f@syzkaller.appspotmail.com
Closes: https://lkml.kernel.org/r/00000000000019a97c05fd42f8c8@google.com
Fixes: 7f42ec394156 ("nilfs2: fix issue with race condition of competition between segments for dirty blocks")
Cc: <stable@vger.kernel.org>
---
Andrew, please apply this as a bugfix.

This fixes a kernel bug issue reported by syzbot.  This may conflict
with the merged folio conversion series when backporting it to stable
trees.  I would like to send a separate request to the stable team
in that case.

Thanks,
Ryusuke Konishi

 fs/nilfs2/segment.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index 2590a0860eab..2bfb08052d39 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -1703,7 +1703,6 @@ static void nilfs_segctor_prepare_write(struct nilfs_sc_info *sci)
 
 		list_for_each_entry(bh, &segbuf->sb_payload_buffers,
 				    b_assoc_buffers) {
-			set_buffer_async_write(bh);
 			if (bh == segbuf->sb_super_root) {
 				if (bh->b_folio != bd_folio) {
 					folio_lock(bd_folio);
@@ -1714,6 +1713,7 @@ static void nilfs_segctor_prepare_write(struct nilfs_sc_info *sci)
 				}
 				break;
 			}
+			set_buffer_async_write(bh);
 			if (bh->b_folio != fs_folio) {
 				nilfs_begin_folio_io(fs_folio);
 				fs_folio = bh->b_folio;
@@ -1800,7 +1800,6 @@ static void nilfs_abort_logs(struct list_head *logs, int err)
 
 		list_for_each_entry(bh, &segbuf->sb_payload_buffers,
 				    b_assoc_buffers) {
-			clear_buffer_async_write(bh);
 			if (bh == segbuf->sb_super_root) {
 				clear_buffer_uptodate(bh);
 				if (bh->b_folio != bd_folio) {
@@ -1809,6 +1808,7 @@ static void nilfs_abort_logs(struct list_head *logs, int err)
 				}
 				break;
 			}
+			clear_buffer_async_write(bh);
 			if (bh->b_folio != fs_folio) {
 				nilfs_end_folio_io(fs_folio, err);
 				fs_folio = bh->b_folio;
@@ -1896,8 +1896,9 @@ static void nilfs_segctor_complete_write(struct nilfs_sc_info *sci)
 				 BIT(BH_Delay) | BIT(BH_NILFS_Volatile) |
 				 BIT(BH_NILFS_Redirected));
 
-			set_mask_bits(&bh->b_state, clear_bits, set_bits);
 			if (bh == segbuf->sb_super_root) {
+				set_buffer_uptodate(bh);
+				clear_buffer_dirty(bh);
 				if (bh->b_folio != bd_folio) {
 					folio_end_writeback(bd_folio);
 					bd_folio = bh->b_folio;
@@ -1905,6 +1906,7 @@ static void nilfs_segctor_complete_write(struct nilfs_sc_info *sci)
 				update_sr = true;
 				break;
 			}
+			set_mask_bits(&bh->b_state, clear_bits, set_bits);
 			if (bh->b_folio != fs_folio) {
 				nilfs_end_folio_io(fs_folio, 0);
 				fs_folio = bh->b_folio;
-- 
2.34.1