On Mon, 18 Oct 2010 14:23:51 -0700 Hari Subramanian <hari@xxxxxxxxxx> wrote: > Is this bug found in the raid1 personality driver as well? No. It is possible there are other problems in raid1 which I am investigating at the moment. But this bug isn't in raid1. NeilBrown > > Thanks > ~ Hari > > > -----Original Message----- > From: linux-raid-owner@xxxxxxxxxxxxxxx [mailto:linux-raid-owner@xxxxxxxxxxxxxxx] On Behalf Of Neil Brown > Sent: Monday, August 09, 2010 4:11 AM > To: ravichandra > Cc: linux-raid@xxxxxxxxxxxxxxx > Subject: Re: Problem regarding RAID10 on kernel 2.6.31 > > On Mon, 09 Aug 2010 13:09:56 +0530 > ravichandra <vmynidi@xxxxxxxxxxxxxxxxxx> wrote: > > > Hi, > > Thanks.The patch you have sent is working.There is no hanging up > > after the patch is applied.can you elaborate on the problem which was > > there earlier?? > > > > It's .... complicated. > > An important fact is that generic_make_request queues recursive requests > rather than issuing them immediately. This avoids excessive stack usage with > stacked block devices. > > So in the case where a read crosses a chunk boundary, raid10:make_request > issues two separate generic_make_request calls to two different devices, each > preceded by a wait_barrier call (Which is cancelled with allow_barrer() when > the request completes). > The first is queued and will not be issued until the second is also queued and > the raid10:make_request call completes. > > The wait_barrier call increments nr_pending. > If the resync/recovery thread tries to 'raise_barrier' between these calls, > it will find nr_pending set and will wait with ->barrier incremented so when > the next wait_barrier is attempted, is will block - forever. > > If generic_make_request didn't queue things, the first request would > complete, nr_pending would decrement, resync would proceed with a single > request, then the second wait_barrier would complete and the second request > could be submitted. > > The fix was to elevate conf->nr_waiting for the duration of both submissions > so raise_barrier holds off setting ->barrier until both submissions are > complete. > > Hope that makes sense. > > NeilBrown > > -- > 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 -- 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
