[syzbot] WARNING in nilfs_dat_prepare_end

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: a962b54e162c Merge tag 'i2c-for-6.0-rc8' of git://git.kern..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=16708124880000
kernel config: https://syzkaller.appspot.com/x/.config?x=ba0d23aa7e1ffaf5
dashboard link: https://syzkaller.appspot.com/bug?extid=5d5d25f90f195a3cfcb4
compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=165b2f98880000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12c20e82880000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/7cf7771c181a/disk-a962b54e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/dcd5516984d8/vmlinux-a962b54e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5d5d25...@syzkaller.appspotmail.com

NILFS (loop0): segctord starting. Construction interval = 5 seconds, CP frequency < 30 seconds
------------[ cut here ]------------
WARNING: CPU: 0 PID: 3609 at fs/nilfs2/dat.c:151 nilfs_dat_prepare_end+0x247/0x2a0
Modules linked in:
CPU: 0 PID: 3609 Comm: segctord Not tainted 6.0.0-rc7-syzkaller-00250-ga962b54e162c #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/22/2022
RIP: 0010:nilfs_dat_prepare_end+0x247/0x2a0 fs/nilfs2/dat.c:151
Code: 3f 40 fe 89 eb 89 d8 48 83 c4 10 5b 41 5c 41 5d 41 5e 41 5f 5d c3 e8 b8 3f 40 fe e8 b3 3c b9 fd e9 5a ff ff ff e8 a9 3f 40 fe <0f> 0b bb fe ff ff ff eb d2 44 89 f9 80 e1 07 80 c1 03 38 c1 0f 8c
RSP: 0018:ffffc9000390f310 EFLAGS: 00010293
RAX: ffffffff834749d7 RBX: 00000000fffffffe RCX: ffff888027003b00
RDX: 0000000000000000 RSI: 00000000fffffffe RDI: 00000000fffffffe
RBP: 1ffff92000721e7c R08: ffffffff83474950 R09: ffffffff834596a3
R10: 0000000000000002 R11: ffff888027003b00 R12: ffffc9000390f3e0
R13: ffff88804cf90158 R14: ffffc9000390f3f8 R15: dffffc0000000000
FS: 0000000000000000(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055db1609ac08 CR3: 000000000c88e000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
nilfs_dat_prepare_update+0x1f/0xd0 fs/nilfs2/dat.c:223
nilfs_direct_propagate+0x1c2/0x390 fs/nilfs2/direct.c:274
nilfs_bmap_propagate+0x6d/0x120 fs/nilfs2/bmap.c:337
nilfs_segctor_apply_buffers+0x192/0x380 fs/nilfs2/segment.c:1012
nilfs_segctor_scan_file+0x8b5/0xaf0 fs/nilfs2/segment.c:1072
nilfs_segctor_collect_blocks fs/nilfs2/segment.c:1170 [inline]
nilfs_segctor_collect fs/nilfs2/segment.c:1497 [inline]
nilfs_segctor_do_construct+0x1cce/0x6fe0 fs/nilfs2/segment.c:2039
nilfs_segctor_construct+0x143/0x8d0 fs/nilfs2/segment.c:2375
nilfs_segctor_thread_construct fs/nilfs2/segment.c:2483 [inline]
nilfs_segctor_thread+0x534/0x1180 fs/nilfs2/segment.c:2566
kthread+0x266/0x300 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306
</TASK>


---
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 syzk...@googlegroups.com.

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syzbot can test patches for this issue, for details see:
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[Ryusuke Konishi]

If DAT metadata file block access fails due to corruption of the DAT file
or abnormal virtual block numbers held by b-trees or inodes, a kernel
warning is generated.

This replaces the WARN_ONs by error output, so that a kernel, booted with
panic_on_warn, does not panic. This patch also replaces the detected
return code -ENOENT with another internal code -EINVAL to notify the bmap
layer of metadata corruption. When the bmap layer sees -EINVAL, it
handles the abnormal situation with nilfs_bmap_convert_error() and
finally returns code -EIO as it should.

Link: https://lkml.kernel.org/r/0000000000005c...@google.com
Signed-off-by: Ryusuke Konishi <konishi...@gmail.com>
Reported-by: syzbot+5d5d25...@syzkaller.appspotmail.com
Tested-by: Ryusuke Konishi <konishi...@gmail.com>
---
Hi Andrew, please queue this. This fixes a few potential WARN_ONs
for corrupted disk images like the one syzbot produced.

Thanks,
Ryusuke Konishi

fs/nilfs2/dat.c | 27 +++++++++++++++++----------
1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/fs/nilfs2/dat.c b/fs/nilfs2/dat.c
index 9930fa901039..1e7f653c1df7 100644
--- a/fs/nilfs2/dat.c
+++ b/fs/nilfs2/dat.c
@@ -40,8 +40,21 @@ static inline struct nilfs_dat_info *NILFS_DAT_I(struct inode *dat)
static int nilfs_dat_prepare_entry(struct inode *dat,
struct nilfs_palloc_req *req, int create)
{
- return nilfs_palloc_get_entry_block(dat, req->pr_entry_nr,
- create, &req->pr_entry_bh);
+ int ret;
+
+ ret = nilfs_palloc_get_entry_block(dat, req->pr_entry_nr,
+ create, &req->pr_entry_bh);
+ if (unlikely(ret == -ENOENT)) {
+ nilfs_err(dat->i_sb,
+ "DAT doesn't have a block to manage vblocknr = %llu",
+ (unsigned long long)req->pr_entry_nr);
+ /*
+ * Return internal code -EINVAL to notify bmap layer of
+ * metadata corruption.
+ */
+ ret = -EINVAL;
+ }
+ return ret;
}

static void nilfs_dat_commit_entry(struct inode *dat,
@@ -123,11 +136,7 @@ static void nilfs_dat_commit_free(struct inode *dat,

int nilfs_dat_prepare_start(struct inode *dat, struct nilfs_palloc_req *req)
{
- int ret;
-
- ret = nilfs_dat_prepare_entry(dat, req, 0);
- WARN_ON(ret == -ENOENT);
- return ret;
+ return nilfs_dat_prepare_entry(dat, req, 0);
}

void nilfs_dat_commit_start(struct inode *dat, struct nilfs_palloc_req *req,
@@ -154,10 +163,8 @@ int nilfs_dat_prepare_end(struct inode *dat, struct nilfs_palloc_req *req)
int ret;

ret = nilfs_dat_prepare_entry(dat, req, 0);
- if (ret < 0) {
- WARN_ON(ret == -ENOENT);
+ if (ret < 0)
return ret;
- }

kaddr = kmap_atomic(req->pr_entry_bh->b_page);
entry = nilfs_palloc_block_get_entry(dat, req->pr_entry_nr,
--
2.34.1