On Sat, Oct 10, 2015 at 3:52 AM, Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > On Thu, Oct 08 2015 at 11:08am -0400, > Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > >> On Thu, Oct 08 2015 at 11:04am -0400, >> Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: >> >> > >> > >> > On Tue, 6 Oct 2015, Mike Snitzer wrote: >> > >> > > To give others context for why I'm caring about this issue again, this >> > > recent BZ against 4.3-rc served as a reminder that we _need_ a fix: >> > > https://bugzilla.redhat.com/show_bug.cgi?id=1267650 >> > > >> > > FYI, I cleaned up the plug-based approach a bit further, here is the >> > > incremental patch: >> > > http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/commit/?h=wip&id=f73d001ec692125308accbb5ca26f892f949c1b6 >> > > >> > > And here is a new version of the overall combined patch (sharing now >> > > before I transition to looking at alternatives, though my gut is the use >> > > of a plug in generic_make_request really wouldn't hurt us.. famous last >> > > words): >> > > >> > > block/bio.c | 82 +++++++++++++------------------------------------- >> > > block/blk-core.c | 21 ++++++++----- >> > > drivers/md/dm-bufio.c | 2 +- >> > > drivers/md/raid1.c | 6 ++-- >> > > drivers/md/raid10.c | 6 ++-- >> > > include/linux/blkdev.h | 11 +++++-- >> > > include/linux/sched.h | 4 --- >> > > 7 files changed, 51 insertions(+), 81 deletions(-) >> > > >> ... >> > > diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c >> > > index 2dd3308..c2bff16 100644 >> > > --- a/drivers/md/dm-bufio.c >> > > +++ b/drivers/md/dm-bufio.c >> > > @@ -168,7 +168,7 @@ static inline int dm_bufio_cache_index(struct dm_bufio_client *c) >> > > #define DM_BUFIO_CACHE(c) (dm_bufio_caches[dm_bufio_cache_index(c)]) >> > > #define DM_BUFIO_CACHE_NAME(c) (dm_bufio_cache_names[dm_bufio_cache_index(c)]) >> > > >> > > -#define dm_bufio_in_request() (!!current->bio_list) >> > > +#define dm_bufio_in_request() (current->plug && !!current->plug->bio_list) >> > >> > This condition is repeated several times throughout the whole patch - so >> > maybe you should make it a function in block device header file. >> >> Yeah, I thought of that too but forgot to come back to it. Will do, >> thanks. >> >> FYI, I found another bug in my last patch and fixed it up. I'll get >> some refactoring done (including your suggestion), actually _test_ the >> code (e.g. verify all of lvm testsuite passes) and then send out v3. > > 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). Looks you should have defined bio_list in plug as 'struct bio_list bio_list' instead of one pointer. > > 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. Looks this problem should be related with above 'bio_list' definition too. > > 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): > > Mike > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- Ming Lei -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
