Re: [md PATCH 2/3] md: remove md_super_wait() call after bitmap_flush()

[Shaohua Li <shli@kernel.org>]

On Thu, Nov 10, 2016 at 11:57:35AM +1100, Neil Brown wrote:
> On Thu, Nov 10 2016, Shaohua Li wrote:
> 
> > On Wed, Nov 09, 2016 at 10:21:32AM +1100, Neil Brown wrote:
> >> bitmap_flush() finishes with bitmap_update_sb(), and that finishes
> >> with write_page(..., 1), so write_page() will wait for all writes
> >> to complete.  So there is no point calling md_super_wait()
> >> immediately afterwards.
> >> 
> >> Signed-off-by: NeilBrown <neilb@suse.com>
> >> ---
> >>  drivers/md/md.c |    1 -
> >>  1 file changed, 1 deletion(-)
> >> 
> >> diff --git a/drivers/md/md.c b/drivers/md/md.c
> >> index f389d8abe137..1f1c7f007b68 100644
> >> --- a/drivers/md/md.c
> >> +++ b/drivers/md/md.c
> >> @@ -5472,7 +5472,6 @@ static void __md_stop_writes(struct mddev *mddev)
> >>  	del_timer_sync(&mddev->safemode_timer);
> >>  
> >>  	bitmap_flush(mddev);
> >> -	md_super_wait(mddev);
> >
> > bitmap_flush() could be null if there is no bitmap, is this safe?
> 
> Good question.
> If there is no bitmap, then all metadata updates (both superblock
> and bad-block-list) are synchronous in md_update_sb(), which is always
> called under ->reconfig_mutex and so which cannot race with this code.
> 
> So yes, it is safe.  That md_super_wait() was only ever intended to wait
> for things that bitmap_flush() might have flushed, so it should have
> been inside that function.

Ah, yes, md_super_wait follows all md_super_write. It should be safe.
Applied, thanks!