From: Eric Biggers <ebiggers@kernel.org>
To: Gao Xiang <hsiangkao@gmx.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>,
kernel-team@android.com, linux-kernel@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: get parent inode when recovering pino
Date: Tue, 5 May 2020 18:24:28 -0700 [thread overview]
Message-ID: <20200506012428.GG128280@sol.localdomain> (raw)
In-Reply-To: <20200506001403.GA2101@hsiangkao-HP-ZHAN-66-Pro-G1>
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.
- Eric
next prev parent reply other threads:[~2020-05-06 1:24 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-05 15:31 [PATCH] f2fs: get parent inode when recovering pino Jaegeuk Kim
2020-05-05 16:58 ` [f2fs-dev] " Eric Biggers
2020-05-05 17:59 ` Eric Biggers
2020-05-05 18:20 ` Jaegeuk Kim
2020-05-05 18:13 ` Jaegeuk Kim
2020-05-05 18:19 ` Eric Biggers
2020-05-05 18:49 ` Jaegeuk Kim
2020-05-05 19:01 ` Eric Biggers
2020-05-05 19:08 ` Jaegeuk Kim
2020-05-06 0:14 ` Gao Xiang
2020-05-06 1:24 ` Eric Biggers [this message]
2020-05-06 1:58 ` Gao Xiang
2020-05-06 6:47 ` Gao Xiang
2020-05-06 19:16 ` Eric Biggers
2020-05-06 22:36 ` Gao Xiang
2020-05-07 6:38 ` Chao Yu
2020-05-07 7:23 ` Gao Xiang
2020-05-06 6:55 ` Chao Yu
2020-05-07 6:30 ` Chao Yu
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