[PATCH AUTOSEL 5.8 022/132] xfs: Set xfs_buf's b_ops member when zeroing bitmap/summary files

Sasha Levin
2020-10-27T00:30:57Z

From: Chandan Babu R <chandanrlinux@gmail.com>

[ Upstream commit c54e14d155f5fdbac73a8cd4bd2678cb252149dc ]

In xfs_growfs_rt(), we enlarge bitmap and summary files by allocating
new blocks for both files. For each of the new blocks allocated, we
allocate an xfs_buf, zero the payload, log the contents and commit the
transaction. Hence these buffers will eventually find themselves
appended to list at xfs_ail->ail_buf_list.

Later, xfs_growfs_rt() loops across all of the new blocks belonging to
the bitmap inode to set the bitmap values to 1. In doing so, it
allocates a new transaction and invokes the following sequence of
functions,
- xfs_rtfree_range()
- xfs_rtmodify_range()
- xfs_rtbuf_get()
We pass '&xfs_rtbuf_ops' as the ops pointer to xfs_trans_read_buf().
- xfs_trans_read_buf()
We find the xfs_buf of interest in per-ag hash table, invoke
xfs_buf_reverify() which ends up assigning '&xfs_rtbuf_ops' to
xfs_buf->b_ops.

On the other hand, if xfs_growfs_rt_alloc() had allocated a few blocks
for the bitmap inode and returned with an error, all the xfs_bufs
corresponding to the new bitmap blocks that have been allocated would
continue to be on xfs_ail->ail_buf_list list without ever having a
non-NULL value assigned to their b_ops members. An AIL flush operation
would then trigger the following warning message to be printed on the
console,

XFS (loop0): _xfs_buf_ioapply: no buf ops on daddr 0x58 len 8
00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
CPU: 3 PID: 449 Comm: xfsaild/loop0 Not tainted 5.8.0-rc4-chandan-00038-g4d8c2b9de9ab-dirty #37
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
Call Trace:
dump_stack+0x57/0x70
_xfs_buf_ioapply+0x37c/0x3b0
? xfs_rw_bdev+0x1e0/0x1e0
? xfs_buf_delwri_submit_buffers+0xd4/0x210
__xfs_buf_submit+0x6d/0x1f0
xfs_buf_delwri_submit_buffers+0xd4/0x210
xfsaild+0x2c8/0x9e0
? __switch_to_asm+0x42/0x70
? xfs_trans_ail_cursor_first+0x80/0x80
kthread+0xfe/0x140
? kthread_park+0x90/0x90
ret_from_fork+0x22/0x30

This message indicates that the xfs_buf had its b_ops member set to
NULL.

This commit fixes the issue by assigning "&xfs_rtbuf_ops" to b_ops
member of each of the xfs_bufs logged by xfs_growfs_rt_alloc().

Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/xfs/xfs_rtalloc.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/fs/xfs/xfs_rtalloc.c b/fs/xfs/xfs_rtalloc.c
index 04b953c3ffa75..48be55b18c494 100644
--- a/fs/xfs/xfs_rtalloc.c
+++ b/fs/xfs/xfs_rtalloc.c
@@ -838,6 +838,7 @@ xfs_growfs_rt_alloc(
goto out_trans_cancel;

xfs_trans_buf_set_type(tp, bp, buf_type);
+ bp->b_ops = &xfs_rtbuf_ops;
memset(bp->b_addr, 0, mp->m_sb.sb_blocksize);
xfs_trans_log_buf(tp, bp, 0, mp->m_sb.sb_blocksize - 1);
/*
--
2.25.1