From patchwork Wed Jun 29 00:18:06 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mikulas Patocka X-Patchwork-Id: 9204125 X-Patchwork-Delegate: snitzer@redhat.com Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 7DF9360757 for ; Wed, 29 Jun 2016 00:21:43 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 692432862C for ; Wed, 29 Jun 2016 00:21:43 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 5AF3E2862F; Wed, 29 Jun 2016 00:21:43 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from mx3-phx2.redhat.com (mx3-phx2.redhat.com [209.132.183.24]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 893A92862C for ; Wed, 29 Jun 2016 00:21:41 +0000 (UTC) Received: from lists01.pubmisc.prod.ext.phx2.redhat.com (lists01.pubmisc.prod.ext.phx2.redhat.com [10.5.19.33]) by mx3-phx2.redhat.com (8.13.8/8.13.8) with ESMTP id u5T0I8iA026888; Tue, 28 Jun 2016 20:18:08 -0400 Received: from int-mx11.intmail.prod.int.phx2.redhat.com (int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.24]) by lists01.pubmisc.prod.ext.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id u5T0I7bw004669 for ; Tue, 28 Jun 2016 20:18:07 -0400 Received: from file01.intranet.prod.int.rdu2.redhat.com (file01.intranet.prod.int.rdu2.redhat.com [10.11.5.7]) by int-mx11.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u5T0I6Vl014193 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Tue, 28 Jun 2016 20:18:07 -0400 Received: from file01.intranet.prod.int.rdu2.redhat.com (localhost [127.0.0.1]) by file01.intranet.prod.int.rdu2.redhat.com (8.14.4/8.14.4) with ESMTP id u5T0I6nw008037; Tue, 28 Jun 2016 20:18:06 -0400 Received: from localhost (mpatocka@localhost) by file01.intranet.prod.int.rdu2.redhat.com (8.14.4/8.14.4/Submit) with ESMTP id u5T0I6RY008033; Tue, 28 Jun 2016 20:18:06 -0400 X-Authentication-Warning: file01.intranet.prod.int.rdu2.redhat.com: mpatocka owned process doing -bs Date: Tue, 28 Jun 2016 20:18:06 -0400 (EDT) From: Mikulas Patocka X-X-Sender: mpatocka@file01.intranet.prod.int.rdu2.redhat.com To: "Alasdair G. Kergon" , Mike Snitzer , Zdenek Kabelac Message-ID: User-Agent: Alpine 2.02 (LRH 1266 2009-07-14) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.68 on 10.5.11.24 X-loop: dm-devel@redhat.com Cc: dm-devel@redhat.com Subject: [dm-devel] [PATCH 1/3] block: flush queued bios when process blocks to avoid deadlock X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com X-Virus-Scanned: ClamAV using ClamSMTP >From f126e182a053ef2e44a3e70b86df84d2b003530b Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Tue, 27 May 2014 11:03:36 -0400 Subject: block: flush queued bios when process blocks to avoid deadlock The block layer uses per-process bio list to avoid recursion in generic_make_request. When generic_make_request is called recursively, the bio is added to current->bio_list and generic_make_request returns immediately. The top-level instance of generic_make_request takes bios from current->bio_list and processes them. Commit df2cb6daa4 ("block: Avoid deadlocks with bio allocation by stacking drivers") created a workqueue for every bio set and code in bio_alloc_bioset() that tries to resolve some low-memory deadlocks by redirecting bios queued on current->bio_list to the workqueue if the system is low on memory. However another deadlock (see below **) may happen, without any low memory condition, because generic_make_request is queuing bios to current->bio_list (rather than submitting them). Fix this deadlock by redirecting any bios on current->bio_list to the bio_set's rescue workqueue on every schedule call. Consequently, when the process blocks on a mutex, the bios queued on current->bio_list are dispatched to independent workqueus and they can complete without waiting for the mutex to be available. Also, now we can remove punt_bios_to_rescuer() and bio_alloc_bioset()'s calls to it because bio_alloc_bioset() will implicitly punt all bios on current->bio_list if it performs a blocking allocation. ** Here is the dm-snapshot deadlock that was observed: 1) Process A sends one-page read bio to the dm-snapshot target. The bio spans snapshot chunk boundary and so it is split to two bios by device mapper. 2) Device mapper creates the first sub-bio and sends it to the snapshot driver. 3) The function snapshot_map calls track_chunk (that allocates a structure dm_snap_tracked_chunk and adds it to tracked_chunk_hash) and then remaps the bio to the underlying device and exits with DM_MAPIO_REMAPPED. 4) The remapped bio is submitted with generic_make_request, but it isn't issued - it is added to current->bio_list instead. 5) Meanwhile, process B (dm's kcopyd) executes pending_complete for the chunk affected be the first remapped bio, it takes down_write(&s->lock) and then loops in __check_for_conflicting_io, waiting for dm_snap_tracked_chunk created in step 3) to be released. 6) Process A continues, it creates a second sub-bio for the rest of the original bio. 7) snapshot_map is called for this new bio, it waits on down_write(&s->lock) that is held by Process B (in step 5). Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1267650 Signed-off-by: Mikulas Patocka Signed-off-by: Mike Snitzer Depends-on: df2cb6daa4 ("block: Avoid deadlocks with bio allocation by stacking drivers") Cc: stable@vger.kernel.org --- block/bio.c | 75 ++++++++++++++++++------------------------------- include/linux/blkdev.h | 24 +++++++++++---- kernel/sched/core.c | 7 +--- 3 files changed, 48 insertions(+), 58 deletions(-) -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel Index: linux-4.7-rc5-devel/block/bio.c =================================================================== --- linux-4.7-rc5-devel.orig/block/bio.c 2016-06-27 14:25:25.000000000 +0200 +++ linux-4.7-rc5-devel/block/bio.c 2016-06-27 14:27:36.000000000 +0200 @@ -349,35 +349,35 @@ static void bio_alloc_rescue(struct work } } -static void punt_bios_to_rescuer(struct bio_set *bs) +/** + * blk_flush_bio_list + * @tsk: task_struct whose bio_list must be flushed + * + * Pop bios queued on @tsk->bio_list and submit each of them to + * their rescue workqueue. + * + * If the bio doesn't have a bio_set, we leave it on @tsk->bio_list. + * However, stacking drivers should use bio_set, so this shouldn't be + * an issue. + */ +void blk_flush_bio_list(struct task_struct *tsk) { - struct bio_list punt, nopunt; struct bio *bio; + struct bio_list list = *tsk->bio_list; + bio_list_init(tsk->bio_list); - /* - * In order to guarantee forward progress we must punt only bios that - * were allocated from this bio_set; otherwise, if there was a bio on - * there for a stacking driver higher up in the stack, processing it - * could require allocating bios from this bio_set, and doing that from - * our own rescuer would be bad. - * - * Since bio lists are singly linked, pop them all instead of trying to - * remove from the middle of the list: - */ - - bio_list_init(&punt); - bio_list_init(&nopunt); - - while ((bio = bio_list_pop(current->bio_list))) - bio_list_add(bio->bi_pool == bs ? &punt : &nopunt, bio); - - *current->bio_list = nopunt; - - spin_lock(&bs->rescue_lock); - bio_list_merge(&bs->rescue_list, &punt); - spin_unlock(&bs->rescue_lock); + while ((bio = bio_list_pop(&list))) { + struct bio_set *bs = bio->bi_pool; + if (unlikely(!bs)) { + bio_list_add(tsk->bio_list, bio); + continue; + } - queue_work(bs->rescue_workqueue, &bs->rescue_work); + spin_lock(&bs->rescue_lock); + bio_list_add(&bs->rescue_list, bio); + queue_work(bs->rescue_workqueue, &bs->rescue_work); + spin_unlock(&bs->rescue_lock); + } } /** @@ -417,7 +417,6 @@ static void punt_bios_to_rescuer(struct */ struct bio *bio_alloc_bioset(gfp_t gfp_mask, int nr_iovecs, struct bio_set *bs) { - gfp_t saved_gfp = gfp_mask; unsigned front_pad; unsigned inline_vecs; unsigned long idx = BIO_POOL_NONE; @@ -452,23 +451,11 @@ struct bio *bio_alloc_bioset(gfp_t gfp_m * reserve. * * We solve this, and guarantee forward progress, with a rescuer - * workqueue per bio_set. If we go to allocate and there are - * bios on current->bio_list, we first try the allocation - * without __GFP_DIRECT_RECLAIM; if that fails, we punt those - * bios we would be blocking to the rescuer workqueue before - * we retry with the original gfp_flags. + * workqueue per bio_set. If an allocation would block (due to + * __GFP_DIRECT_RECLAIM) the scheduler will first punt all bios + * on current->bio_list to the rescuer workqueue. */ - - if (current->bio_list && !bio_list_empty(current->bio_list)) - gfp_mask &= ~__GFP_DIRECT_RECLAIM; - p = mempool_alloc(bs->bio_pool, gfp_mask); - if (!p && gfp_mask != saved_gfp) { - punt_bios_to_rescuer(bs); - gfp_mask = saved_gfp; - p = mempool_alloc(bs->bio_pool, gfp_mask); - } - front_pad = bs->front_pad; inline_vecs = BIO_INLINE_VECS; } @@ -481,12 +468,6 @@ struct bio *bio_alloc_bioset(gfp_t gfp_m if (nr_iovecs > inline_vecs) { bvl = bvec_alloc(gfp_mask, nr_iovecs, &idx, bs->bvec_pool); - if (!bvl && gfp_mask != saved_gfp) { - punt_bios_to_rescuer(bs); - gfp_mask = saved_gfp; - bvl = bvec_alloc(gfp_mask, nr_iovecs, &idx, bs->bvec_pool); - } - if (unlikely(!bvl)) goto err_free; Index: linux-4.7-rc5-devel/include/linux/blkdev.h =================================================================== --- linux-4.7-rc5-devel.orig/include/linux/blkdev.h 2016-06-27 14:25:25.000000000 +0200 +++ linux-4.7-rc5-devel/include/linux/blkdev.h 2016-06-27 14:27:37.000000000 +0200 @@ -1114,6 +1114,22 @@ static inline bool blk_needs_flush_plug( !list_empty(&plug->cb_list)); } +extern void blk_flush_bio_list(struct task_struct *tsk); + +static inline void blk_flush_queued_io(struct task_struct *tsk) +{ + /* + * Flush any queued bios to corresponding rescue threads. + */ + if (tsk->bio_list && !bio_list_empty(tsk->bio_list)) + blk_flush_bio_list(tsk); + /* + * Flush any plugged IO that is queued. + */ + if (blk_needs_flush_plug(tsk)) + blk_schedule_flush_plug(tsk); +} + /* * tag stuff */ @@ -1722,16 +1738,10 @@ static inline void blk_flush_plug(struct { } -static inline void blk_schedule_flush_plug(struct task_struct *task) +static inline void blk_flush_queued_io(struct task_struct *tsk) { } - -static inline bool blk_needs_flush_plug(struct task_struct *tsk) -{ - return false; -} - static inline int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask, sector_t *error_sector) { Index: linux-4.7-rc5-devel/kernel/sched/core.c =================================================================== --- linux-4.7-rc5-devel.orig/kernel/sched/core.c 2016-06-27 14:26:04.000000000 +0200 +++ linux-4.7-rc5-devel/kernel/sched/core.c 2016-06-27 14:26:38.000000000 +0200 @@ -3359,11 +3359,10 @@ static inline void sched_submit_work(str if (!tsk->state || tsk_is_pi_blocked(tsk)) return; /* - * If we are going to sleep and we have plugged IO queued, + * If we are going to sleep and we have queued IO, * make sure to submit it to avoid deadlocks. */ - if (blk_needs_flush_plug(tsk)) - blk_schedule_flush_plug(tsk); + blk_flush_queued_io(tsk); } asmlinkage __visible void __sched schedule(void) @@ -4977,7 +4976,7 @@ long __sched io_schedule_timeout(long ti long ret; current->in_iowait = 1; - blk_schedule_flush_plug(current); + blk_flush_queued_io(current); delayacct_blkio_start(); rq = raw_rq();