[dm-devel] Re: [RFC][PATCH] dm-mirror: fix data corruption

[malahal at us.ibm.com]

Takahiro Yasui [tyasui at redhat.com] wrote:
> On 07/10/09 09:49, Mikulas Patocka wrote:
> > patch to hold back bios --- untested (and not quite optimal because it 
> > scans the "failures" list in fixed intervals), but it shows the approach.
> > 
> > ---
> >  drivers/md/dm-raid1.c          |   10 +++++++---
> >  drivers/md/dm-region-hash.c    |    6 +-----
> >  include/linux/dm-region-hash.h |    3 +--
> >  3 files changed, 9 insertions(+), 10 deletions(-)
> > 
> > Index: linux-2.6.31-rc2-devel/drivers/md/dm-raid1.c
> > ===================================================================
> > --- linux-2.6.31-rc2-devel.orig/drivers/md/dm-raid1.c	2009-07-10 14:48:19.000000000 +0200
> > +++ linux-2.6.31-rc2-devel/drivers/md/dm-raid1.c	2009-07-10 15:46:11.000000000 +0200
> > @@ -535,11 +535,11 @@ static void write_callback(unsigned long
> >  		else
> >  			uptodate = 1;
> >  
> > -	if (unlikely(!uptodate)) {
> > +	if (unlikely(!uptodate) || !errors_handled(ms)) {
> >  		DMERR("All replicated volumes dead, failing I/O");
> >  		/* None of the writes succeeded, fail the I/O. */
> >  		ret = -EIO;
> > -	} else if (errors_handled(ms)) {
> > +	} else {
> >  		/*
> >  		 * Need to raise event.  Since raising
> >  		 * events can block, we need to do it in
> > @@ -687,8 +687,12 @@ static void do_failures(struct mirror_se
> >  	if (!ms->log_failure) {
> >  		while ((bio = bio_list_pop(failures))) {
> >  			ms->in_sync = 0;
> > -			dm_rh_mark_nosync(ms->rh, bio, bio->bi_size, 0);
> > +			dm_rh_mark_nosync(ms->rh, bio);
> > +			spin_lock_irq(&ms->lock);
> > +			bio_list_add(&ms->failures, bio);
> > +			spin_unlock_irq(&ms->lock);
> >  		}
> > +		delayed_wake(ms);
> >  		return;
> >  	}
> >  
> > Index: linux-2.6.31-rc2-devel/drivers/md/dm-region-hash.c
> > ===================================================================
> > --- linux-2.6.31-rc2-devel.orig/drivers/md/dm-region-hash.c	2009-07-10 14:54:07.000000000 +0200
> > +++ linux-2.6.31-rc2-devel/drivers/md/dm-region-hash.c	2009-07-10 15:45:07.000000000 +0200
> > @@ -392,8 +392,6 @@ static void complete_resync_work(struct 
> >  /* dm_rh_mark_nosync
> >   * @ms
> >   * @bio
> > - * @done
> > - * @error
> >   *
> >   * The bio was written on some mirror(s) but failed on other mirror(s).
> >   * We can successfully endio the bio but should avoid the region being
> > @@ -401,8 +399,7 @@ static void complete_resync_work(struct 
> >   *
> >   * This function is _not_ safe in interrupt context!
> >   */
> > -void dm_rh_mark_nosync(struct dm_region_hash *rh,
> > -		       struct bio *bio, unsigned done, int error)
> > +void dm_rh_mark_nosync(struct dm_region_hash *rh, struct bio *bio)
> >  {
> >  	unsigned long flags;
> >  	struct dm_dirty_log *log = rh->log;
> > @@ -439,7 +436,6 @@ void dm_rh_mark_nosync(struct dm_region_
> >  	BUG_ON(!list_empty(&reg->list));
> >  	spin_unlock_irqrestore(&rh->region_lock, flags);
> >  
> > -	bio_endio(bio, error);
> 
> How do bios queued in ms->failures are processed later? It seems that
> the bios stay in ms->failures forever, and the upper layer can not
> receive "success" for those bios. Don't we need a mechanism to block/unblock
> write bios to fix this issue?

A user level program, dmeventd, may reconfigure the mirror resulting in
submitting the queued I/O's after the reconfiguration.