Re: [PATCH] exfat: remove EXFAT_SB_DIRTY flag

[Tetsuhiro Kohada]

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@xxxxxxxxx>
> > ---
> >   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  âdo nothing when wait is 0â 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?


> > +	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@xxxxxxxxx>