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f2fs: reduce the scope of setting fsck tag when de->name_len is zero

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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: ddf06b753a ("f2fs: fix to trigger fsck if dirent.name_len is zero")
Signed-off-by: Yangtao Li <frank.li@vivo.com>
[Chao: clean up description]
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
This commit is contained in:
Yangtao Li 2021-08-04 11:29:46 +08:00 committed by Jaegeuk Kim
parent 91803392c7
commit d4bf15a7ce
1 changed files with 9 additions and 5 deletions
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14
fs/f2fs/dir.c
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@ -1000,6 +1000,7 @@ int f2fs_fill_dentries(struct dir_context *ctx, struct f2fs_dentry_ptr *d,
struct f2fs_sb_info *sbi = F2FS_I_SB(d->inode);
struct blk_plug plug;
bool readdir_ra = sbi->readdir_ra == 1;
bool found_valid_dirent = false;
int err = 0;
bit_pos = ((unsigned long)ctx->pos % d->max);
@ -1014,13 +1015,15 @@ int f2fs_fill_dentries(struct dir_context *ctx, struct f2fs_dentry_ptr *d,
de = &d->dentry[bit_pos];
if (de->name_len == 0) {
if (found_valid_dirent || !bit_pos) {
printk_ratelimited(
"%sF2FS-fs (%s): invalid namelen(0), ino:%u, run fsck to fix.",
KERN_WARNING, sbi->sb->s_id,
le32_to_cpu(de->ino));
set_sbi_flag(sbi, SBI_NEED_FSCK);
}
bit_pos++;
ctx->pos = start_pos + bit_pos;
printk_ratelimited(
"%sF2FS-fs (%s): invalid namelen(0), ino:%u, run fsck to fix.",
KERN_WARNING, sbi->sb->s_id,
le32_to_cpu(de->ino));
set_sbi_flag(sbi, SBI_NEED_FSCK);
continue;
}
@ -1063,6 +1066,7 @@ int f2fs_fill_dentries(struct dir_context *ctx, struct f2fs_dentry_ptr *d,
f2fs_ra_node_page(sbi, le32_to_cpu(de->ino));
ctx->pos = start_pos + bit_pos;
found_valid_dirent = true;
}
out:
if (readdir_ra)