From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Snitzer Subject: Re: [PATCH v2] block: flush queued bios when the process blocks Date: Fri, 9 Oct 2015 15:59:07 -0400 Message-ID: <20151009195907.GB18790@redhat.com> References: <5384CE82.90601@kernel.dk> <20151005205943.GB25762@redhat.com> <20151006185016.GA31955@redhat.com> <20151006201637.GA4158@redhat.com> <20151008150859.GA11770@redhat.com> <20151009195203.GA18790@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20151009195203.GA18790@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: Mikulas Patocka Cc: Jens Axboe , kent.overstreet@gmail.com, dm-devel@redhat.com, linux-kernel@vger.kernel.org, "Alasdair G. Kergon" List-Id: dm-devel.ids On Fri, Oct 09 2015 at 3:52pm -0400, Mike Snitzer wrote: > Turns out that this change: > http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/commit/?h=wip&id=2639638c77768a86216be456c2764e32a2bcd841 > > needed to be reverted with: > http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/commit/?h=wip&id=ad3ccd760da7c05b90775372f9b39dc2964086fe > > Because nested plugs caused generic_make_request()'s onstack bio_list to > go out of scope (blk_finish_plug() wouldn't actually flush the list > within generic_make_request because XFS already added an outermost > plug). > > But even after fixing that I then hit issues with these changes now > resulting in imperfect 'in_generic_make_request' accounting that happens > lazily once the outermost plug completes blk_finish_plug. manifested as > dm-bufio.c:dm_bufio_prefetch's BUG_ON(dm_bufio_in_request()); hitting. > > Basically using the blk-core's onstack plugging isn't workable for > fixing this deadlock and we're back to having to seriously consider > this (with its additional hook in the scheduler): http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/commit/?h=wip&id=a91709cd32b5ca7ca047b68c9299e747f2ae6ca2