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I recently found a case where de->name_len is 0 in f2fs_fill_dentries()
easily reproduced, and finally set the fsck flag.
Thread A Thread B
- f2fs_readdir
- f2fs_read_inline_dir
- ctx->pos = d.max
- f2fs_add_dentry
- f2fs_add_inline_entry
- do_convert_inline_dir
- f2fs_add_regular_entry
- f2fs_readdir
- f2fs_fill_dentries
- set_sbi_flag(sbi, SBI_NEED_FSCK)
Process A opens the folder, and has been reading without closing it.
During this period, Process B created a file under the folder (occupying
multiple f2fs_dir_entry, exceeding the d.max of the inline dir). After
creation, process A uses the d.max of inline dir to read it again, and
it will read that de->name_len is 0.
And Chao pointed out that w/o inline conversion, the race condition still
can happen as below:
dir_entry1: A
dir_entry2: B
dir_entry3: C
free slot: _
ctx->pos: ^
Thread A is traversing directory,
ctx-pos moves to below position after readdir() by thread A:
AAAABBBB___
^
Then thread B delete dir_entry2, and create dir_entry3.
Thread A calls readdir() to lookup dirents starting from middle
of new dirent slots as below:
AAAACCCCCC_
^
In these scenarios, the file system is not damaged, and it's hard to
avoid it. But we can bypass tagging FSCK flag if:
a) bit_pos (:= ctx->pos % d->max) is non-zero and
b) before bit_pos moves to first valid dir_entry.
Fixes:
|
||
|---|---|---|
| .. | ||
| acl.c | ||
| acl.h | ||
| checkpoint.c | ||
| compress.c | ||
| data.c | ||
| debug.c | ||
| dir.c | ||
| extent_cache.c | ||
| f2fs.h | ||
| file.c | ||
| gc.c | ||
| gc.h | ||
| hash.c | ||
| inline.c | ||
| inode.c | ||
| Kconfig | ||
| Makefile | ||
| namei.c | ||
| node.c | ||
| node.h | ||
| recovery.c | ||
| segment.c | ||
| segment.h | ||
| shrinker.c | ||
| super.c | ||
| sysfs.c | ||
| verity.c | ||
| xattr.c | ||
| xattr.h | ||