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? -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
