RE: [PATCH] exfat: remove EXFAT_SB_DIRTY flag

Sungjong Seo
2020-06-15T03:00:00Z

> On 2020/06/12 17:34, Sungjong Seo wrote:
> >> remove EXFAT_SB_DIRTY flag and related codes.
> >>
> >> This flag is set/reset in exfat_put_super()/exfat_sync_fs() to avoid
> >> sync_blockdev().
> >> However ...
> >> - exfat_put_super():
> >> Before calling this, the VFS has already called sync_filesystem(), so
> >> sync is never performed here.
> >> - exfat_sync_fs():
> >> After calling this, the VFS calls sync_blockdev(), so, it is
> >> meaningless to check EXFAT_SB_DIRTY or to bypass sync_blockdev() here.
> >> Not only that, but in some cases can't clear VOL_DIRTY.
> >> ex:
> >> VOL_DIRTY is set when rmdir starts, but when non-empty-dir is
> >> detected, return error without setting EXFAT_SB_DIRTY.
> >> If performe 'sync' in this state, VOL_DIRTY will not be cleared.
> >>
> >> Remove the EXFAT_SB_DIRTY check to ensure synchronization.
> >> And, remove the code related to the flag.
> >>
> >> Signed-off-by: Tetsuhiro Kohada <kohada.t2@gmail.com>
> >> ---
> >> fs/exfat/balloc.c | 4 ++--
> >> fs/exfat/dir.c | 16 ++++++++--------
> >> fs/exfat/exfat_fs.h | 5 +----
> >> fs/exfat/fatent.c | 7 ++-----
> >> fs/exfat/misc.c | 3 +--
> >> fs/exfat/namei.c | 12 ++++++------
> >> fs/exfat/super.c | 11 +++--------
> >> 7 files changed, 23 insertions(+), 35 deletions(-)
> >>
> > [snip]
> >>
> >> @@ -62,11 +59,9 @@ static int exfat_sync_fs(struct super_block *sb,
> >> int
> >> wait)
> >>
> >> /* If there are some dirty buffers in the bdev inode */
> >> mutex_lock(&sbi->s_lock);
> >> - if (test_and_clear_bit(EXFAT_SB_DIRTY, &sbi->s_state)) {
> >> - sync_blockdev(sb->s_bdev);
> >> - if (exfat_set_vol_flags(sb, VOL_CLEAN))
> >> - err = -EIO;
> >> - }
> >
> > I looked through most codes related to EXFAT_SB_DIRTY and VOL_DIRTY.
> > And your approach looks good because all of them seem to be protected
> > by s_lock.
> >
> > BTW, as you know, sync_filesystem() calls sync_fs() with 'nowait'
> > first, and then calls it again with 'wait' twice. No need to sync with
> lock twice.
> > If so, isn't it okay to do nothing when wait is 0?
>
> I also think ‘do nothing when wait is 0’ as you say, but I'm still not
> sure.
>
> Some other Filesystems do nothing with nowait and just return.
> However, a few Filesystems always perform sync.
>
> sync_blockdev() waits for completion, so it may be inappropriate to call
> with nowait. (But it was called in the original code)
>
> I'm still not sure, so I excluded it in this patch.
> Is it okay to include it?
>

Yes, I think so. sync_filesystem() will call __sync_blockdev() without 'wait' first.
So, it's enough to call sync_blockdev() with s_lock just one time.

>
> >> + sync_blockdev(sb->s_bdev);
> >> + if (exfat_set_vol_flags(sb, VOL_CLEAN))
> >> + err = -EIO;
> >> mutex_unlock(&sbi->s_lock);
> >> return err;
> >> }
> >> --
> >> 2.25.1
> >
> >
>
> BR
> ---
> Tetsuhiro Kohada <kohada.t2@gmail.com>