On Wed, Mar 09, 2016 at 12:58:25PM +1100, Neil Brown wrote: > > break_stripe_batch_list breaks up a batch and copies some flags from > the batch head to the members, preserving others. > > It doesn't preserve or copy STRIPE_PREREAD_ACTIVE. This is not > normally a problem as STRIPE_PREREAD_ACTIVE is cleared when a > stripe_head is added to a batch, and is not set on stripe_heads > already in a batch. > > However there is no locking to ensure one thread doesn't set the flag > after it has just been cleared in another. This does occasionally happen. > > md/raid5 maintains a count of the number of stripe_heads with > STRIPE_PREREAD_ACTIVE set: conf->preread_active_stripes. When > break_stripe_batch_list clears STRIPE_PREREAD_ACTIVE inadvertently > this could becomes incorrect and will never again return to zero. > > md/raid5 delays the handling of some stripe_heads until > preread_active_stripes becomes zero. So when the above mention race > happens, those stripe_heads become blocked and never progress, > resulting is write to the array handing. > > So: change break_stripe_batch_list to preserve STRIPE_PREREAD_ACTIVE > in the members of a batch. > > URL: https://bugzilla.kernel.org/show_bug.cgi?id=108741 > URL: https://bugzilla.redhat.com/show_bug.cgi?id=1258153 > URL: http://thread.gmane.org/[email protected] > Reported-by: Martin Svec <[email protected]> (and others) > Tested-by: Tom Weber <[email protected]> > Fixes: 1b956f7a8f9a ("md/raid5: be more selective about distributing flags > across batch.") > Cc: [email protected] (v4.1 and later) > Signed-off-by: NeilBrown <[email protected]>
Applied, thanks Neil! I'll split the WARN_ON_ONCE and do it for each bit, so next time we can have clear clue. Thanks, Shaohua > --- > drivers/md/raid5.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c > index b4f02c9959f2..2e7d253be6ce 100644 > --- a/drivers/md/raid5.c > +++ b/drivers/md/raid5.c > @@ -4236,7 +4236,6 @@ static void break_stripe_batch_list(struct stripe_head > *head_sh, > WARN_ON_ONCE(sh->state & ((1 << STRIPE_ACTIVE) | > (1 << STRIPE_SYNCING) | > (1 << STRIPE_REPLACED) | > - (1 << STRIPE_PREREAD_ACTIVE) | > (1 << STRIPE_DELAYED) | > (1 << STRIPE_BIT_DELAY) | > (1 << STRIPE_FULL_WRITE) | > @@ -4251,6 +4250,7 @@ static void break_stripe_batch_list(struct stripe_head > *head_sh, > (1 << STRIPE_REPLACED))); > > set_mask_bits(&sh->state, ~(STRIPE_EXPAND_SYNC_FLAGS | > + (1 << STRIPE_PREREAD_ACTIVE) | > (1 << STRIPE_DEGRADED)), > head_sh->state & (1 << STRIPE_INSYNC)); > > -- > 2.7.2 >
