HI Chao, From: Chao Yu <[email protected]> Date: 2021-07-17 16:56:01 To: Yangtao Li <[email protected]>,[email protected] Cc: [email protected],[email protected] Subject: Re: [f2fs-dev] [PATCH] f2fs: fix ctx->pos in f2fs_read_inline_dir()>On 2021/7/17 11:49, Yangtao Li wrote: >> 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. > >Nice catch! > >> >> And returning early in f2fs_read_inline_dir will cause the process to be >> unable to see >> the changes before reopening the file. >> >> So don't return early and remove the modification of ctx->pos in >> f2fs_read_inline_dir(). >> >> Signed-off-by: Yangtao Li <[email protected]> >> --- >> fs/f2fs/inline.c | 5 ----- >> 1 file changed, 5 deletions(-) >> >> diff --git a/fs/f2fs/inline.c b/fs/f2fs/inline.c >> index 56a20d5c15da..fc6551139a3d 100644 >> --- a/fs/f2fs/inline.c >> +++ b/fs/f2fs/inline.c >> @@ -729,9 +729,6 @@ int f2fs_read_inline_dir(struct file *file, struct >> dir_context *ctx, >> >> make_dentry_ptr_inline(inode, &d, inline_dentry); >> >> - if (ctx->pos == d.max) >> - return 0; >> - >> ipage = f2fs_get_node_page(F2FS_I_SB(inode), inode->i_ino); >> if (IS_ERR(ipage)) >> return PTR_ERR(ipage); >> @@ -747,8 +744,6 @@ int f2fs_read_inline_dir(struct file *file, struct >> dir_context *ctx, >> make_dentry_ptr_inline(inode, &d, inline_dentry); >> >> err = f2fs_fill_dentries(ctx, &d, 0, fstr); > >After this function, ctx->pos will point to start position of first free slot >after >last dir_entry, we can't guarantee that the free slot won't be used in above >race >condition, right? > >Moreover, w/o inline conversion, the race condition still can happen as below, >right? > >dir_entry1: A >dir_entry2: B >dir_entry3: C >free slot: _ > >Before: >AAAABBBB___ > ^ >Thread B delete dir_entry2, and create dir_entry3. > >After: >AAAACCCCC__ > ^
Taking into account the above situations, I think this case where de->name_len is 0 in f2fs_fill_dentries() should be normal and there is no way to avoid it. Maybe we shouldn't set fsck flag at this time? Because the file system is not damaged. MBR / Yangtao _______________________________________________ Linux-f2fs-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
