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2f3d93e210
When I enabled ext4 debug for fault injection testing, I encountered the
following warning:
EXT4-fs error (device sda): ext4_read_inode_bitmap:201: comm fsstress:
Cannot read inode bitmap - block_group = 8, inode_bitmap = 1051
WARNING: CPU: 0 PID: 511 at fs/buffer.c:1181 mark_buffer_dirty+0x1b3/0x1d0
The root cause of the issue lies in the improper implementation of ext4's
buffer_head read fault injection. The actual completion of buffer_head
read and the buffer_head fault injection are not atomic, which can lead
to the uptodate flag being cleared on normally used buffer_heads in race
conditions.
[CPU0] [CPU1] [CPU2]
ext4_read_inode_bitmap
ext4_read_bh()
<bh read complete>
ext4_read_inode_bitmap
if (buffer_uptodate(bh))
return bh
jbd2_journal_commit_transaction
__jbd2_journal_refile_buffer
__jbd2_journal_unfile_buffer
__jbd2_journal_temp_unlink_buffer
ext4_simulate_fail_bh()
clear_buffer_uptodate
mark_buffer_dirty
<report warning>
WARN_ON_ONCE(!buffer_uptodate(bh))
The best approach would be to perform fault injection in the IO completion
callback function, rather than after IO completion. However, the IO
completion callback function cannot get the fault injection code in sb.
Fix it by passing the result of fault injection into the bh read function,
we simulate faults within the bh read function itself. This requires adding
an extra parameter to the bh read functions that need fault injection.
Fixes: 46f870d690fe ("ext4: simulate various I/O and checksum errors when reading metadata")
Signed-off-by: Long Li <leo.lilong@huawei.com>
Link: https://patch.msgid.link/20240906091746.510163-1-leo.lilong@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>