On Thu, Mar 10 2016, Shaohua Li wrote: > 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/5649C0E9.2030204@xxxxxxxx >> Reported-by: Martin Svec <martin.svec@xxxxxxxx> (and others) >> Tested-by: Tom Weber <linux@xxxxxxxxxxxxxxxx> >> Fixes: 1b956f7a8f9a ("md/raid5: be more selective about distributing flags across batch.") >> Cc: stable@xxxxxxxxxxxxxxx (v4.1 and later) >> Signed-off-by: NeilBrown <neilb@xxxxxxxx> > > Applied, thanks Neil! I'll split the WARN_ON_ONCE and do it for each bit, so > next time we can have clear clue. I personally think that would look ugly and increase the in-line code size for minimal gain. If you want to make a change (which I'm in two minds about) I think it would be much cleaner to do if (WARN_ON_ONCE(...)) printk(....); Then at least the extra code will be out of line - not even loaded into the instruction cache until needed. Thanks, NeilBrown > > 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 >>
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