Hello, md_update_sb does not clean MD_CHANGE_PENDING flag for imsm arrays (i.e. external == 1). And until MD_CHANGE_PENDING is set all remaining or new IO will not be finished but will stay in return_bi list. Regards, Aleskey -----Original Message----- From: Shaohua Li [mailto:shli@xxxxxxxxxx] Sent: Wednesday, 20 July, 2016 00:46 To: Obitotskiy, Aleksey <aleksey.obitotskiy@xxxxxxxxx> Cc: linux-raid@xxxxxxxxxxxxxxx Subject: Re: [PATCH] md: Prevent IO hold during accessing to failed raid5 array On Fri, Jul 15, 2016 at 03:24:27PM +0200, Alexey Obitotskiy wrote: > After array enters in failed state (e.g. number of failed drives > becomes more then accepted for raid5 level) it sets error flags (one > of this flags is MD_CHANGE_PENDING). This flag prevents to finish all > new or non-finished IOs to array and hold them in pending state. In > some cases this can leads to deadlock situation. > > For example udev handle array state changes (drives becomes faulty) > and blkid started but unable to finish reads due to IO hold. > At the same time we unable to get exclusive access to array (to stop > array in our case) because another external application still use this > array (blkid in our case). > > Fix makes possible to return IO with errors immediately. > So external application can finish working with array and give > exclusive access to other applications. > > Signed-off-by: Alexey Obitotskiy <aleksey.obitotskiy@xxxxxxxxx> > --- > drivers/md/raid5.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index > 6c1149d..99471b6 100644 > --- a/drivers/md/raid5.c > +++ b/drivers/md/raid5.c > @@ -4692,7 +4692,9 @@ finish: > } > > if (!bio_list_empty(&s.return_bi)) { > - if (test_bit(MD_CHANGE_PENDING, &conf->mddev->flags)) { > + if (test_bit(MD_CHANGE_PENDING, &conf->mddev->flags) && > + (s.failed <= conf->max_degraded || > + conf->mddev->external == 0)) { > spin_lock_irq(&conf->device_lock); > bio_list_merge(&conf->return_bi, &s.return_bi); > spin_unlock_irq(&conf->device_lock); > -- > 2.7.4 Hi Alexey, I'm not clear about the race. When we set the MD_CHANGE_PENDING, we will schedule superblock write, which will eventually finish (either success or timedout). Why will the IO be hold forever? Thanks, Shaohua -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
