Re: [PATCH 4/6] md: don't export log device

[Shaohua Li <shli@fb.com>]

On Thu, Oct 08, 2015 at 12:57:29PM +1100, Neil Brown wrote:
> Shaohua Li <shli@fb.com> writes:
> 
> > If there is IO error in log device, don't export it like other raid
> > disks. Otherwise we get kernel crash in different places since
> > rdev->bdev, rdev->mddev becomes NULL
> >
> > Signed-off-by: Shaohua Li <shli@fb.com>
> > ---
> >  drivers/md/md.c    | 4 ++--
> >  drivers/md/raid5.c | 2 ++
> >  2 files changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/md/md.c b/drivers/md/md.c
> > index c643c9a..ec6574d 100644
> > --- a/drivers/md/md.c
> > +++ b/drivers/md/md.c
> > @@ -2523,7 +2523,7 @@ state_store(struct md_rdev *rdev, const char *buf, size_t len)
> >  		else
> >  			err = -EBUSY;
> >  	} else if (cmd_match(buf, "remove")) {
> > -		if (rdev->raid_disk >= 0)
> > +		if (rdev->raid_disk >= 0 || test_bit(Journal, &rdev->flags))
> >  			err = -EBUSY;
> >  		else {
> >  			struct mddev *mddev = rdev->mddev;
> > @@ -6044,7 +6044,7 @@ static int hot_remove_disk(struct mddev *mddev, dev_t dev)
> >  	clear_bit(Blocked, &rdev->flags);
> >  	remove_and_add_spares(mddev, rdev);
> >  
> > -	if (rdev->raid_disk >= 0)
> > +	if (rdev->raid_disk >= 0 || test_bit(Journal, &rdev->flags))
> >  		goto busy;
> >  
> >  	if (mddev_is_clustered(mddev))
> 
> Neither of these chunks should be needed.
> ->raid_disk of an active devices is only set to -1 if ->hot_remove_disk
> succeeds.
> You have make ->hot_remove_disk fail for Journal devices, so ->raid_disk
> will be >= 0.

I agree the raid5_remove_disk part is superficial, I fixed in an updated
patch. I still didn't get the point what can prevent a journal disk is
removed. Currently the raid_disk is always -1 for journal disk. If it
should be >=0, what value it should be? We give journal disk a special
role '0xfffd' currently.

Thanks,
shaohua
> 
> > diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> > index 216fa3c..c164501 100644
> > --- a/drivers/md/raid5.c
> > +++ b/drivers/md/raid5.c
> > @@ -7128,6 +7128,8 @@ static int raid5_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
> >  	struct disk_info *p = conf->disks + number;
> >  
> >  	print_raid5_conf(conf);
> > +	if (test_bit(Journal, &rdev->flags))
> > +		return -EBUSY;
> >  	if (rdev == p->rdev)
> >  		rdevp = &p->rdev;
> >  	else if (rdev == p->replacement)
> > -- 
> > 2.4.6