[cc'ing linux-block and drbd folks] On Tue, Jun 28 2016 at 8:16pm -0400, Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > Hi > > Here I'm sending three patches to fix the deadlocks in snapshot and > snapshot-merge. > > The first patch fixes the deadlock, the following 2 patches introduce a > timer, so that bios are not offloaded immediatelly, they are offloaded > after a specified timeout, because immediate offloading can change order > of bios and it could theoretically produce regressions. I don't know if > these regressions really exist or not. > > If there is some way to push the patches upstream, try it. Some fix must happen before the more recent upstream kernels can be reliably used in stacked bio-based workloads (in production). We simply cannot ignore this issue any more. drbd is also hitting the same generic_make_request (current->bio_list) problem, see: https://www.redhat.com/archives/dm-devel/2016-June/msg00326.html Mikulas, I've taken your 3 proposed patches patches and refactored them some to split out intermediate patches that hopefully make review easier. Nothing other than variable names and some other style stuff was changed -- headers were tweaked some to help with clarity. Please see the 5 topmost "block: ..." patches here: http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/log/?h=wip It should be noted that Jens had a quick look at this set and wanted to throw up a little when he saw the (ab)use of a timer to defer punting to the workqueue. I explained that without the timer, always punting to the workqueue, we could hurt performance by reordering IO or crippling onstack plugging. He said he'd try to think of a cleaner way forward. Lars, please feel free to see if this set addresses the similar deadlock you saw/fixed with drbd. We need to converge on an acceptable fix for this problem -- preferably sooner rather than later! Conversely, Mikulas: if you can easily reproduce the dm-snapshot deadlock please try Lars' fix to see if it is workable for our DM needs. Thanks, Mike p.s. I'm on holiday until next Wednesday (7/6).. so may be slow to respond until then. -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
