On Mon, 4 Nov 2013, Mike Snitzer wrote: > On Mon, Nov 04 2013 at 10:06am -0500, > Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > > > > > > > On Fri, 1 Nov 2013, Jens Axboe wrote: > > > > > On 11/01/2013 07:59 AM, Mike Snitzer wrote: > > > > Add the missing bi_remaining increment, required by the block layer's > > > > new bio-chaining code, to both the verity and old snapshot DM targets. > > > > > > > > Otherwise users will hit the bi_remaining <= 0 BUG_ON in bio_endio(). > > > > > > Thanks Mike, added to the mix. > > > > > > -- > > > Jens Axboe > > > > Hi > > > > This improves a little bit on the previous patch, by replacing costly > > atomic_inc with cheap atomic_set. > > > > > > From: Mikulas Patocka <mpatocka@xxxxxxxxxx> > > > > dm: change atomic_inc to atomic_set(1) > > > > There are places in dm where we save bi_endio and bi_private, set them to > > target's routine, submit the bio, from the target's bi_endio routine we > > restore bi_endio and bi_private and end the bio with bi_endio. > > > > This causes underflow of bi_remaining, so we must restore bi_remaining > > before ending the bio from the target bi_endio routine. > > > > The code uses atomic_inc for restoration of bi_remaining. This patch > > changes it to atomic_set(1) to avoid an interlocked instruction. In the > > target's bi_endio routine we are sure that bi_remaining is zero > > (otherwise, the bi_endio routine wouldn't be called) and there are no > > concurrent users of the bio, so we can replace atomic_inc with > > atomic_set(1). > > This isn't DM-specific. Shouldn't the other places in the tree that use > atomic_inc on bi_remaining should really be converted at the same time? There is no 'atomic_inc.*bi_remaining' in other drivers. It is just in fs/bio.c in bio_chain and bio_endio_nodec where it's probably needed. Mikulas -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
