lkml.org 
[lkml]   [2020]   [May]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [f2fs-dev] [PATCH] f2fs: get parent inode when recovering pino
From
Date
On 2020/5/6 14:55, Chao Yu wrote:
> On 2020/5/6 9:24, Eric Biggers wrote:
>> On Wed, May 06, 2020 at 08:14:07AM +0800, Gao Xiang wrote:
>>>>
>>>> Actually, I think this is wrong because the fsync can be done via a file
>>>> descriptor that was opened to a now-deleted link to the file.
>>>
>>> I'm still confused about this...
>>>
>>> I don't know what's wrong with this version from my limited knowledge?
>>> inode itself is locked when fsyncing, so
>>>
>>> if the fsync inode->i_nlink == 1, this inode has only one hard link
>>> (not deleted yet) and should belong to a single directory; and
>>>
>>> the only one parent directory would not go away (not deleted as well)
>>> since there are some dirents in it (not empty).
>>>
>>> Could kindly explain more so I would learn more about this scenario?
>>> Thanks a lot!
>>
>> i_nlink == 1 just means that there is one non-deleted link. There can be links
>> that have since been deleted, and file descriptors can still be open to them.
>>
>>>
>>>>
>>>> We need to find the dentry whose parent directory is still exists, i.e. the
>>>> parent directory that is counting towards 'inode->i_nlink == 1'.
>>>
>>> directory counting towards 'inode->i_nlink == 1', what's happening?
>>
>> The non-deleted link is the one counted in i_nlink.
>>
>>>
>>>>
>>>> I think d_find_alias() is what we're looking for.
>>>
>>> It may be simply dentry->d_parent (stable/positive as you said before, and it's
>>> not empty). why need to d_find_alias()?
>>
>> Because we need to get the dentry that hasn't been deleted yet, which isn't
>> necessarily the one associated with the file descriptor being fsync()'ed.
>>
>>> And what is the original problem? I could not get some clue from the original
>>> patch description (I only saw some extra igrab/iput because of some unknown
>>> reasons), it there some backtrace related to the problem?
>>
>> The problem is that i_pino gets set incorrectly. I just noticed this while
>> reviewing the code. It's not hard to reproduce, e.g.:
>>
>> #include <unistd.h>
>> #include <fcntl.h>
>> #include <sys/stat.h>
>>
>> int main()
>> {
>> int fd;
>>
>> mkdir("dir1", 0700);
>> mkdir("dir2", 0700);
>> mknod("dir1/file", S_IFREG|0600, 0);
>> link("dir1/file", "dir2/file");
>> fd = open("dir2/file", O_WRONLY);
>> unlink("dir2/file");
>> write(fd, "X", 1);
>> fsync(fd);
>> }
>>
>> Then:
>>
>> sync
>> echo N | dump.f2fs -i $(stat -c %i dir1/file) /dev/vdb | grep 'i_pino'
>> echo "dir1 (correct): $(stat -c %i dir1)"
>> echo "dir2 (wrong): $(stat -c %i dir2)"
>>
>> i_pino will point to dir2 rather than dir1 as expected.
>
> Could you add above testcase into commit message of your patch? it will
> be easier to understand the issue we solved with it.
>
> In addition, how about adding this testcase in fstest as a generic one?

Oops, it's not a generic one... please ignore this.

>
>>
>> - Eric
>>
>>
>> _______________________________________________
>> Linux-f2fs-devel mailing list
>> Linux-f2fs-devel@lists.sourceforge.net
>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>> .
>>
>
>
> _______________________________________________
> Linux-f2fs-devel mailing list
> Linux-f2fs-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
> .
>

\
 
 \ /
  Last update: 2020-05-07 08:31    [W:0.079 / U:1.736 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site