From patchwork Thu Dec 20 18:06:49 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nikos Tsironis X-Patchwork-Id: 10739269 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-2.web.codeaurora.org (Postfix) with ESMTP id 5286E6C2 for ; Thu, 20 Dec 2018 18:07:25 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 401F228DC2 for ; Thu, 20 Dec 2018 18:07:25 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 343D228DB7; Thu, 20 Dec 2018 18:07:25 +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=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id BD64E28DB7 for ; Thu, 20 Dec 2018 18:07:24 +0000 (UTC) Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 544EB142C0E; Thu, 20 Dec 2018 18:07:23 +0000 (UTC) Received: from colo-mx.corp.redhat.com (colo-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.21]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 248622B5BF; Thu, 20 Dec 2018 18:07:23 +0000 (UTC) Received: from lists01.pubmisc.prod.ext.phx2.redhat.com (lists01.pubmisc.prod.ext.phx2.redhat.com [10.5.19.33]) by colo-mx.corp.redhat.com (Postfix) with ESMTP id DC15F245FB; Thu, 20 Dec 2018 18:07:22 +0000 (UTC) Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) by lists01.pubmisc.prod.ext.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id wBKI73V5026596 for ; Thu, 20 Dec 2018 13:07:03 -0500 Received: by smtp.corp.redhat.com (Postfix) id 1F53D7D873; Thu, 20 Dec 2018 18:07:03 +0000 (UTC) Delivered-To: dm-devel@redhat.com Received: from mx1.redhat.com (ext-mx09.extmail.prod.ext.phx2.redhat.com [10.5.110.38]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 88DAA1822E; Thu, 20 Dec 2018 18:06:55 +0000 (UTC) Received: from mx0.arrikto.com (mx0.arrikto.com [212.71.252.59]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id BF5F6E8B16; Thu, 20 Dec 2018 18:06:53 +0000 (UTC) Received: from troi.prod.arr (mail.arr [10.99.0.5]) by mx0.arrikto.com (Postfix) with ESMTP id DDE68182005; Thu, 20 Dec 2018 20:06:51 +0200 (EET) Received: from snf-864.vm.snf.arr (snf-864.vm.snf.arr [10.97.70.29]) by troi.prod.arr (Postfix) with ESMTPSA id 94A4C325; Thu, 20 Dec 2018 20:06:51 +0200 (EET) From: Nikos Tsironis To: snitzer@redhat.com, agk@redhat.com, dm-devel@redhat.com Date: Thu, 20 Dec 2018 20:06:49 +0200 Message-Id: <20181220180651.4879-2-ntsironis@arrikto.com> In-Reply-To: <20181220180651.4879-1-ntsironis@arrikto.com> References: <20181220180651.4879-1-ntsironis@arrikto.com> X-Greylist: Sender passed SPF test, ACL 238 matched, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Thu, 20 Dec 2018 18:06:54 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Thu, 20 Dec 2018 18:06:54 +0000 (UTC) for IP:'212.71.252.59' DOMAIN:'mx0.arrikto.com' HELO:'mx0.arrikto.com' FROM:'ntsironis@arrikto.com' RCPT:'' X-RedHat-Spam-Score: -0.001 (SPF_PASS) 212.71.252.59 mx0.arrikto.com 212.71.252.59 mx0.arrikto.com X-Scanned-By: MIMEDefang 2.78 on 10.5.110.38 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-loop: dm-devel@redhat.com Cc: mpatocka@redhat.com, iliastsi@arrikto.com Subject: [dm-devel] [PATCH 1/3] list_bl: Add hlist_bl_add_before/behind helpers 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: , MIME-Version: 1.0 Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Thu, 20 Dec 2018 18:07:23 +0000 (UTC) X-Virus-Scanned: ClamAV using ClamSMTP Add hlist_bl_add_before/behind helpers to add an element before/after an existing element in a bl_list. Signed-off-by: Nikos Tsironis Signed-off-by: Ilias Tsitsimpis --- include/linux/list_bl.h | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) diff --git a/include/linux/list_bl.h b/include/linux/list_bl.h index 3fc2cc57ba1b..2fd918e5fd48 100644 --- a/include/linux/list_bl.h +++ b/include/linux/list_bl.h @@ -86,6 +86,33 @@ static inline void hlist_bl_add_head(struct hlist_bl_node *n, hlist_bl_set_first(h, n); } +static inline void hlist_bl_add_before(struct hlist_bl_node *n, + struct hlist_bl_node *next) +{ + struct hlist_bl_node **pprev = next->pprev; + + n->pprev = pprev; + n->next = next; + next->pprev = &n->next; + + /* pprev may be `first`, so be careful not to lose the lock bit */ + WRITE_ONCE(*pprev, + (struct hlist_bl_node *) + ((unsigned long)n | + ((unsigned long)*pprev & LIST_BL_LOCKMASK))); +} + +static inline void hlist_bl_add_behind(struct hlist_bl_node *n, + struct hlist_bl_node *prev) +{ + n->next = prev->next; + n->pprev = &prev->next; + WRITE_ONCE(prev->next, n); + + if (n->next) + n->next->pprev = &n->next; +} + static inline void __hlist_bl_del(struct hlist_bl_node *n) { struct hlist_bl_node *next = n->next; From patchwork Thu Dec 20 18:06:50 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nikos Tsironis X-Patchwork-Id: 10739263 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-2.web.codeaurora.org (Postfix) with ESMTP id B1A0C6C2 for ; Thu, 20 Dec 2018 18:07:09 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 9AD0528DF6 for ; Thu, 20 Dec 2018 18:07:09 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 8C43928E08; Thu, 20 Dec 2018 18:07:09 +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=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 0473E28DB7 for ; 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Thu, 20 Dec 2018 18:07:01 +0000 (UTC) Delivered-To: dm-devel@redhat.com Received: from mx1.redhat.com (ext-mx09.extmail.prod.ext.phx2.redhat.com [10.5.110.38]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9A2B33844; Thu, 20 Dec 2018 18:06:55 +0000 (UTC) Received: from mx0.arrikto.com (mx0.arrikto.com [212.71.252.59]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 63937D56E7; Thu, 20 Dec 2018 18:06:53 +0000 (UTC) Received: from troi.prod.arr (mail.arr [10.99.0.5]) by mx0.arrikto.com (Postfix) with ESMTP id E0E84182006; Thu, 20 Dec 2018 20:06:51 +0200 (EET) Received: from snf-864.vm.snf.arr (snf-864.vm.snf.arr [10.97.70.29]) by troi.prod.arr (Postfix) with ESMTPSA id A36D93DF; Thu, 20 Dec 2018 20:06:51 +0200 (EET) From: Nikos Tsironis To: snitzer@redhat.com, agk@redhat.com, dm-devel@redhat.com Date: Thu, 20 Dec 2018 20:06:50 +0200 Message-Id: <20181220180651.4879-3-ntsironis@arrikto.com> In-Reply-To: <20181220180651.4879-1-ntsironis@arrikto.com> References: <20181220180651.4879-1-ntsironis@arrikto.com> X-Greylist: Sender passed SPF test, ACL 238 matched, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Thu, 20 Dec 2018 18:06:54 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Thu, 20 Dec 2018 18:06:54 +0000 (UTC) for IP:'212.71.252.59' DOMAIN:'mx0.arrikto.com' HELO:'mx0.arrikto.com' FROM:'ntsironis@arrikto.com' RCPT:'' X-RedHat-Spam-Score: -0.001 (SPF_PASS) 212.71.252.59 mx0.arrikto.com 212.71.252.59 mx0.arrikto.com X-Scanned-By: MIMEDefang 2.78 on 10.5.110.38 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-loop: dm-devel@redhat.com Cc: mpatocka@redhat.com, iliastsi@arrikto.com Subject: [dm-devel] [PATCH 2/3] dm snapshot: Don't sleep holding the snapshot lock 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: , MIME-Version: 1.0 Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Thu, 20 Dec 2018 18:07:07 +0000 (UTC) X-Virus-Scanned: ClamAV using ClamSMTP When completing a pending exception, pending_complete() waits for all conflicting reads to drain, before inserting the final, completed exception. Conflicting reads are snapshot reads redirected to the origin, because the relevant chunk is not remapped to the COW device the moment we receive the read. The completed exception must be inserted into the exception table after all conflicting reads drain to ensure snapshot reads don't return corrupted data. This is required because inserting the completed exception into the exception table signals that the relevant chunk is remapped and both origin writes and snapshot merging will now overwrite the chunk in origin. This wait is done holding the snapshot lock to ensure that pending_complete() doesn't starve if new snapshot reads keep coming for this chunk. In preparation for the next commit, where we use a spinlock instead of a mutex to protect the exception tables, we remove the need for holding the lock while waiting for conflicting reads to drain. We achieve this in two steps: 1. pending_complete() inserts the completed exception before waiting for conflicting reads to drain and removes the pending exception after all conflicting reads drain. This ensures that new snapshot reads will be redirected to the COW device, instead of the origin, and thus pending_complete() will not starve. Moreover, we use the existence of both a completed and a pending exception to signify that the COW is done but there are conflicting reads in flight. 2. In __origin_write() we check first if there is a pending exception and then if there is a completed exception. If there is a pending exception any submitted BIO is delayed on the pe->origin_bios list and DM_MAPIO_SUBMITTED is returned. This ensures that neither writes to the origin nor snapshot merging can overwrite the origin chunk, until all conflicting reads drain, and thus snapshot reads will not return corrupted data. Summarizing, we now have the following possible combinations of pending and completed exceptions for a chunk, along with their meaning: A. No exceptions exist: The chunk has not been remapped yet. B. Only a pending exception exists: The chunk is currently being copied to the COW device. C. Both a pending and a completed exception exist: COW for this chunk has completed but there are snapshot reads in flight which had been redirected to the origin before the chunk was remapped. D. Only the completed exception exists: COW has been completed and there are no conflicting reads in flight. Signed-off-by: Nikos Tsironis Signed-off-by: Ilias Tsitsimpis --- drivers/md/dm-snap.c | 102 ++++++++++++++++++++++++++++++++------------------- 1 file changed, 65 insertions(+), 37 deletions(-) diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c index 36805b12661e..4b34bfa0900a 100644 --- a/drivers/md/dm-snap.c +++ b/drivers/md/dm-snap.c @@ -1501,16 +1501,24 @@ static void pending_complete(void *context, int success) goto out; } - /* Check for conflicting reads */ - __check_for_conflicting_io(s, pe->e.old_chunk); - /* - * Add a proper exception, and remove the - * in-flight exception from the list. + * Add a proper exception. After inserting the completed exception all + * subsequent snapshot reads to this chunk will be redirected to the + * COW device. This ensures that we do not starve. Moreover, as long + * as the pending exception exists, neither origin writes nor snapshot + * merging can overwrite the chunk in origin. */ dm_insert_exception(&s->complete, e); + /* Wait for conflicting reads to drain */ + if (__chunk_is_tracked(s, pe->e.old_chunk)) { + mutex_unlock(&s->lock); + __check_for_conflicting_io(s, pe->e.old_chunk); + mutex_lock(&s->lock); + } + out: + /* Remove the in-flight exception from the list */ dm_remove_exception(&pe->e); snapshot_bios = bio_list_get(&pe->snapshot_bios); origin_bios = bio_list_get(&pe->origin_bios); @@ -1660,25 +1668,15 @@ __lookup_pending_exception(struct dm_snapshot *s, chunk_t chunk) } /* - * Looks to see if this snapshot already has a pending exception - * for this chunk, otherwise it allocates a new one and inserts - * it into the pending table. + * Inserts a pending exception into the pending table. * * NOTE: a write lock must be held on snap->lock before calling * this. */ static struct dm_snap_pending_exception * -__find_pending_exception(struct dm_snapshot *s, - struct dm_snap_pending_exception *pe, chunk_t chunk) +__insert_pending_exception(struct dm_snapshot *s, + struct dm_snap_pending_exception *pe, chunk_t chunk) { - struct dm_snap_pending_exception *pe2; - - pe2 = __lookup_pending_exception(s, chunk); - if (pe2) { - free_pending_exception(pe); - return pe2; - } - pe->e.old_chunk = chunk; bio_list_init(&pe->origin_bios); bio_list_init(&pe->snapshot_bios); @@ -1697,6 +1695,29 @@ __find_pending_exception(struct dm_snapshot *s, return pe; } +/* + * Looks to see if this snapshot already has a pending exception + * for this chunk, otherwise it allocates a new one and inserts + * it into the pending table. + * + * NOTE: a write lock must be held on snap->lock before calling + * this. + */ +static struct dm_snap_pending_exception * +__find_pending_exception(struct dm_snapshot *s, + struct dm_snap_pending_exception *pe, chunk_t chunk) +{ + struct dm_snap_pending_exception *pe2; + + pe2 = __lookup_pending_exception(s, chunk); + if (pe2) { + free_pending_exception(pe); + return pe2; + } + + return __insert_pending_exception(s, pe, chunk); +} + static void remap_exception(struct dm_snapshot *s, struct dm_exception *e, struct bio *bio, chunk_t chunk) { @@ -2107,7 +2128,7 @@ static int __origin_write(struct list_head *snapshots, sector_t sector, int r = DM_MAPIO_REMAPPED; struct dm_snapshot *snap; struct dm_exception *e; - struct dm_snap_pending_exception *pe; + struct dm_snap_pending_exception *pe, *pe2; struct dm_snap_pending_exception *pe_to_start_now = NULL; struct dm_snap_pending_exception *pe_to_start_last = NULL; chunk_t chunk; @@ -2137,17 +2158,17 @@ static int __origin_write(struct list_head *snapshots, sector_t sector, */ chunk = sector_to_chunk(snap->store, sector); - /* - * Check exception table to see if block - * is already remapped in this snapshot - * and trigger an exception if not. - */ - e = dm_lookup_exception(&snap->complete, chunk); - if (e) - goto next_snapshot; - pe = __lookup_pending_exception(snap, chunk); if (!pe) { + /* + * Check exception table to see if block is already + * remapped in this snapshot and trigger an exception + * if not. + */ + e = dm_lookup_exception(&snap->complete, chunk); + if (e) + goto next_snapshot; + mutex_unlock(&snap->lock); pe = alloc_pending_exception(snap); mutex_lock(&snap->lock); @@ -2157,16 +2178,23 @@ static int __origin_write(struct list_head *snapshots, sector_t sector, goto next_snapshot; } - e = dm_lookup_exception(&snap->complete, chunk); - if (e) { + pe2 = __lookup_pending_exception(snap, chunk); + + if (!pe2) { + e = dm_lookup_exception(&snap->complete, chunk); + if (e) { + free_pending_exception(pe); + goto next_snapshot; + } + + pe = __insert_pending_exception(snap, pe, chunk); + if (!pe) { + __invalidate_snapshot(snap, -ENOMEM); + goto next_snapshot; + } + } else { free_pending_exception(pe); - goto next_snapshot; - } - - pe = __find_pending_exception(snap, pe, chunk); - if (!pe) { - __invalidate_snapshot(snap, -ENOMEM); - goto next_snapshot; + pe = pe2; } } From patchwork Thu Dec 20 18:06:51 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nikos Tsironis X-Patchwork-Id: 10739265 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-2.web.codeaurora.org (Postfix) with ESMTP id E30A9161F for ; 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Thu, 20 Dec 2018 18:06:53 +0000 (UTC) Received: from troi.prod.arr (mail.arr [10.99.0.5]) by mx0.arrikto.com (Postfix) with ESMTP id E90BE182007; Thu, 20 Dec 2018 20:06:51 +0200 (EET) Received: from snf-864.vm.snf.arr (snf-864.vm.snf.arr [10.97.70.29]) by troi.prod.arr (Postfix) with ESMTPSA id A95623E0; Thu, 20 Dec 2018 20:06:51 +0200 (EET) From: Nikos Tsironis To: snitzer@redhat.com, agk@redhat.com, dm-devel@redhat.com Date: Thu, 20 Dec 2018 20:06:51 +0200 Message-Id: <20181220180651.4879-4-ntsironis@arrikto.com> In-Reply-To: <20181220180651.4879-1-ntsironis@arrikto.com> References: <20181220180651.4879-1-ntsironis@arrikto.com> X-Greylist: Sender passed SPF test, ACL 238 matched, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Thu, 20 Dec 2018 18:06:54 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Thu, 20 Dec 2018 18:06:54 +0000 (UTC) for IP:'212.71.252.59' DOMAIN:'mx0.arrikto.com' HELO:'mx0.arrikto.com' FROM:'ntsironis@arrikto.com' RCPT:'' X-RedHat-Spam-Score: -0.001 (SPF_PASS) 212.71.252.59 mx0.arrikto.com 212.71.252.59 mx0.arrikto.com X-Scanned-By: MIMEDefang 2.78 on 10.5.110.26 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-loop: dm-devel@redhat.com Cc: mpatocka@redhat.com, iliastsi@arrikto.com Subject: [dm-devel] [PATCH 3/3] dm snapshot: Use fine-grained locking scheme 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: , MIME-Version: 1.0 Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Thu, 20 Dec 2018 18:07:07 +0000 (UTC) X-Virus-Scanned: ClamAV using ClamSMTP dm-snapshot uses a single mutex to serialize every access to the snapshot state. This includes all accesses to the complete and pending exception tables, which occur at every origin write, every snapshot read/write and every exception completion. The lock statistics indicate that this mutex is a bottleneck (average wait time ~480 usecs for 8 processes doing random 4K writes to the origin device) preventing dm-snapshot to scale as the number of threads doing IO increases. The major contention points are __origin_write()/snapshot_map() and pending_complete(), i.e., the submission and completion of pending exceptions. Substitute the single mutex with a fine-grained locking scheme. Use a read-write semaphore to protect the mostly read fields of the snapshot structure, e.g., valid, active, etc., and per-bucket bit spinlocks to protect accesses to the complete and pending exception tables. This scheme allows dm-snapshot to scale better, resulting in increased IOPS and reduced latency. Following are some benchmark results using the null_blk device: modprobe null_blk gb=1024 bs=512 submit_queues=8 hw_queue_depth=4096 \ queue_mode=2 irqmode=1 completion_nsec=1 nr_devices=1 * Benchmark fio_origin_randwrite_throughput_N, from the device mapper test suite [1] (direct IO, random 4K writes to origin device, IO engine libaio): +--------------+-------------+------------+ | # of workers | IOPS Before | IOPS After | +--------------+-------------+------------+ | 1 | 57708 | 66421 | | 2 | 63415 | 77589 | | 4 | 67276 | 98839 | | 8 | 60564 | 109258 | +--------------+-------------+------------+ * Benchmark fio_origin_randwrite_latency_N, from the device mapper test suite [1] (direct IO, random 4K writes to origin device, IO engine psync): +--------------+-----------------------+----------------------+ | # of workers | Latency (usec) Before | Latency (usec) After | +--------------+-----------------------+----------------------+ | 1 | 16.25 | 13.27 | | 2 | 31.65 | 25.08 | | 4 | 55.28 | 41.08 | | 8 | 121.47 | 74.44 | +--------------+-----------------------+----------------------+ * Benchmark fio_snapshot_randwrite_throughput_N, from the device mapper test suite [1] (direct IO, random 4K writes to snapshot device, IO engine libaio): +--------------+-------------+------------+ | # of workers | IOPS Before | IOPS After | +--------------+-------------+------------+ | 1 | 72593 | 84938 | | 2 | 97379 | 134973 | | 4 | 90610 | 143077 | | 8 | 90537 | 180085 | +--------------+-------------+------------+ * Benchmark fio_snapshot_randwrite_latency_N, from the device mapper test suite [1] (direct IO, random 4K writes to snapshot device, IO engine psync): +--------------+-----------------------+----------------------+ | # of workers | Latency (usec) Before | Latency (usec) After | +--------------+-----------------------+----------------------+ | 1 | 12.53 | 10.6 | | 2 | 19.78 | 14.89 | | 4 | 40.37 | 23.47 | | 8 | 89.32 | 48.48 | +--------------+-----------------------+----------------------+ [1] https://github.com/jthornber/device-mapper-test-suite Signed-off-by: Nikos Tsironis Signed-off-by: Ilias Tsitsimpis --- drivers/md/dm-exception-store.h | 3 +- drivers/md/dm-snap.c | 273 +++++++++++++++++++++++++++------------- 2 files changed, 185 insertions(+), 91 deletions(-) diff --git a/drivers/md/dm-exception-store.h b/drivers/md/dm-exception-store.h index 12b5216c2cfe..5a3c696c057f 100644 --- a/drivers/md/dm-exception-store.h +++ b/drivers/md/dm-exception-store.h @@ -11,6 +11,7 @@ #define _LINUX_DM_EXCEPTION_STORE #include +#include #include /* @@ -27,7 +28,7 @@ typedef sector_t chunk_t; * chunk within the device. */ struct dm_exception { - struct list_head hash_list; + struct hlist_bl_node hash_list; chunk_t old_chunk; chunk_t new_chunk; diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c index 4b34bfa0900a..4530d0620a72 100644 --- a/drivers/md/dm-snap.c +++ b/drivers/md/dm-snap.c @@ -13,6 +13,7 @@ #include #include #include +#include #include #include #include @@ -44,11 +45,11 @@ static const char dm_snapshot_merge_target_name[] = "snapshot-merge"; struct dm_exception_table { uint32_t hash_mask; unsigned hash_shift; - struct list_head *table; + struct hlist_bl_head *table; }; struct dm_snapshot { - struct mutex lock; + struct rw_semaphore lock; struct dm_dev *origin; struct dm_dev *cow; @@ -76,7 +77,9 @@ struct dm_snapshot { atomic_t pending_exceptions_count; - /* Protected by "lock" */ + spinlock_t pe_allocation_lock; + + /* Protected by "pe_allocation_lock" */ sector_t exception_start_sequence; /* Protected by kcopyd single-threaded callback */ @@ -457,9 +460,9 @@ static int __find_snapshots_sharing_cow(struct dm_snapshot *snap, if (!bdev_equal(s->cow->bdev, snap->cow->bdev)) continue; - mutex_lock(&s->lock); + down_read(&s->lock); active = s->active; - mutex_unlock(&s->lock); + up_read(&s->lock); if (active) { if (snap_src) @@ -618,6 +621,36 @@ static void unregister_snapshot(struct dm_snapshot *s) * The lowest hash_shift bits of the chunk number are ignored, allowing * some consecutive chunks to be grouped together. */ +static uint32_t exception_hash(struct dm_exception_table *et, chunk_t chunk); + +/* Lock to protect access to the completed and pending exception hash tables. */ +struct dm_exception_table_lock { + struct hlist_bl_head *complete_slot; + struct hlist_bl_head *pending_slot; +}; + +static void dm_exception_table_lock_init(struct dm_snapshot *s, chunk_t chunk, + struct dm_exception_table_lock *lock) +{ + struct dm_exception_table *complete = &s->complete; + struct dm_exception_table *pending = &s->pending; + + lock->complete_slot = &complete->table[exception_hash(complete, chunk)]; + lock->pending_slot = &pending->table[exception_hash(pending, chunk)]; +} + +static void dm_exception_table_lock(struct dm_exception_table_lock *lock) +{ + hlist_bl_lock(lock->complete_slot); + hlist_bl_lock(lock->pending_slot); +} + +static void dm_exception_table_unlock(struct dm_exception_table_lock *lock) +{ + hlist_bl_unlock(lock->pending_slot); + hlist_bl_unlock(lock->complete_slot); +} + static int dm_exception_table_init(struct dm_exception_table *et, uint32_t size, unsigned hash_shift) { @@ -625,12 +658,12 @@ static int dm_exception_table_init(struct dm_exception_table *et, et->hash_shift = hash_shift; et->hash_mask = size - 1; - et->table = dm_vcalloc(size, sizeof(struct list_head)); + et->table = dm_vcalloc(size, sizeof(struct hlist_bl_head)); if (!et->table) return -ENOMEM; for (i = 0; i < size; i++) - INIT_LIST_HEAD(et->table + i); + INIT_HLIST_BL_HEAD(et->table + i); return 0; } @@ -638,15 +671,16 @@ static int dm_exception_table_init(struct dm_exception_table *et, static void dm_exception_table_exit(struct dm_exception_table *et, struct kmem_cache *mem) { - struct list_head *slot; - struct dm_exception *ex, *next; + struct hlist_bl_head *slot; + struct dm_exception *ex; + struct hlist_bl_node *pos, *n; int i, size; size = et->hash_mask + 1; for (i = 0; i < size; i++) { slot = et->table + i; - list_for_each_entry_safe (ex, next, slot, hash_list) + hlist_bl_for_each_entry_safe(ex, pos, n, slot, hash_list) kmem_cache_free(mem, ex); } @@ -660,7 +694,7 @@ static uint32_t exception_hash(struct dm_exception_table *et, chunk_t chunk) static void dm_remove_exception(struct dm_exception *e) { - list_del(&e->hash_list); + hlist_bl_del(&e->hash_list); } /* @@ -670,11 +704,12 @@ static void dm_remove_exception(struct dm_exception *e) static struct dm_exception *dm_lookup_exception(struct dm_exception_table *et, chunk_t chunk) { - struct list_head *slot; + struct hlist_bl_head *slot; + struct hlist_bl_node *pos; struct dm_exception *e; slot = &et->table[exception_hash(et, chunk)]; - list_for_each_entry (e, slot, hash_list) + hlist_bl_for_each_entry(e, pos, slot, hash_list) if (chunk >= e->old_chunk && chunk <= e->old_chunk + dm_consecutive_chunk_count(e)) return e; @@ -721,7 +756,8 @@ static void free_pending_exception(struct dm_snap_pending_exception *pe) static void dm_insert_exception(struct dm_exception_table *eh, struct dm_exception *new_e) { - struct list_head *l; + struct hlist_bl_head *l; + struct hlist_bl_node *pos; struct dm_exception *e = NULL; l = &eh->table[exception_hash(eh, new_e->old_chunk)]; @@ -731,7 +767,7 @@ static void dm_insert_exception(struct dm_exception_table *eh, goto out; /* List is ordered by old_chunk */ - list_for_each_entry_reverse(e, l, hash_list) { + hlist_bl_for_each_entry(e, pos, l, hash_list) { /* Insert after an existing chunk? */ if (new_e->old_chunk == (e->old_chunk + dm_consecutive_chunk_count(e) + 1) && @@ -752,12 +788,24 @@ static void dm_insert_exception(struct dm_exception_table *eh, return; } - if (new_e->old_chunk > e->old_chunk) + if (new_e->old_chunk < e->old_chunk) break; } out: - list_add(&new_e->hash_list, e ? &e->hash_list : l); + if (!e) { + /* + * Either the table doesn't support consecutive chunks or slot + * l is empty. + */ + hlist_bl_add_head(&new_e->hash_list, l); + } else if (new_e->old_chunk < e->old_chunk) { + /* Add before an existing exception */ + hlist_bl_add_before(&new_e->hash_list, &e->hash_list); + } else { + /* Add to l's tail: e is the last exception in this slot */ + hlist_bl_add_behind(&new_e->hash_list, &e->hash_list); + } } /* @@ -766,6 +814,7 @@ static void dm_insert_exception(struct dm_exception_table *eh, */ static int dm_add_exception(void *context, chunk_t old, chunk_t new) { + struct dm_exception_table_lock lock; struct dm_snapshot *s = context; struct dm_exception *e; @@ -778,7 +827,17 @@ static int dm_add_exception(void *context, chunk_t old, chunk_t new) /* Consecutive_count is implicitly initialised to zero */ e->new_chunk = new; + /* + * Although there is no need to lock access to the exception tables + * here, if we don't then hlist_bl_add_head(), called by + * dm_insert_exception(), will complain about accessing the + * corresponding list without locking it first. + */ + dm_exception_table_lock_init(s, old, &lock); + + dm_exception_table_lock(&lock); dm_insert_exception(&s->complete, e); + dm_exception_table_unlock(&lock); return 0; } @@ -807,7 +866,7 @@ static int calc_max_buckets(void) { /* use a fixed size of 2MB */ unsigned long mem = 2 * 1024 * 1024; - mem /= sizeof(struct list_head); + mem /= sizeof(struct hlist_bl_head); return mem; } @@ -927,7 +986,7 @@ static int remove_single_exception_chunk(struct dm_snapshot *s) int r; chunk_t old_chunk = s->first_merging_chunk + s->num_merging_chunks - 1; - mutex_lock(&s->lock); + down_write(&s->lock); /* * Process chunks (and associated exceptions) in reverse order @@ -942,7 +1001,7 @@ static int remove_single_exception_chunk(struct dm_snapshot *s) b = __release_queued_bios_after_merge(s); out: - mutex_unlock(&s->lock); + up_write(&s->lock); if (b) flush_bios(b); @@ -1001,9 +1060,9 @@ static void snapshot_merge_next_chunks(struct dm_snapshot *s) if (linear_chunks < 0) { DMERR("Read error in exception store: " "shutting down merge"); - mutex_lock(&s->lock); + down_write(&s->lock); s->merge_failed = 1; - mutex_unlock(&s->lock); + up_write(&s->lock); } goto shut; } @@ -1044,10 +1103,10 @@ static void snapshot_merge_next_chunks(struct dm_snapshot *s) previous_count = read_pending_exceptions_done_count(); } - mutex_lock(&s->lock); + down_write(&s->lock); s->first_merging_chunk = old_chunk; s->num_merging_chunks = linear_chunks; - mutex_unlock(&s->lock); + up_write(&s->lock); /* Wait until writes to all 'linear_chunks' drain */ for (i = 0; i < linear_chunks; i++) @@ -1089,10 +1148,10 @@ static void merge_callback(int read_err, unsigned long write_err, void *context) return; shut: - mutex_lock(&s->lock); + down_write(&s->lock); s->merge_failed = 1; b = __release_queued_bios_after_merge(s); - mutex_unlock(&s->lock); + up_write(&s->lock); error_bios(b); merge_shutdown(s); @@ -1188,10 +1247,11 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv) s->snapshot_overflowed = 0; s->active = 0; atomic_set(&s->pending_exceptions_count, 0); + spin_lock_init(&s->pe_allocation_lock); s->exception_start_sequence = 0; s->exception_complete_sequence = 0; s->out_of_order_tree = RB_ROOT; - mutex_init(&s->lock); + init_rwsem(&s->lock); INIT_LIST_HEAD(&s->list); spin_lock_init(&s->pe_lock); s->state_bits = 0; @@ -1357,9 +1417,9 @@ static void snapshot_dtr(struct dm_target *ti) /* Check whether exception handover must be cancelled */ (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL); if (snap_src && snap_dest && (s == snap_src)) { - mutex_lock(&snap_dest->lock); + down_write(&snap_dest->lock); snap_dest->valid = 0; - mutex_unlock(&snap_dest->lock); + up_write(&snap_dest->lock); DMERR("Cancelling snapshot handover."); } up_read(&_origins_lock); @@ -1390,8 +1450,6 @@ static void snapshot_dtr(struct dm_target *ti) dm_exception_store_destroy(s->store); - mutex_destroy(&s->lock); - dm_put_device(ti, s->cow); dm_put_device(ti, s->origin); @@ -1467,6 +1525,13 @@ static void __invalidate_snapshot(struct dm_snapshot *s, int err) dm_table_event(s->ti->table); } +static void invalidate_snapshot(struct dm_snapshot *s, int err) +{ + down_write(&s->lock); + __invalidate_snapshot(s, err); + up_write(&s->lock); +} + static void pending_complete(void *context, int success) { struct dm_snap_pending_exception *pe = context; @@ -1475,29 +1540,37 @@ static void pending_complete(void *context, int success) struct bio *origin_bios = NULL; struct bio *snapshot_bios = NULL; struct bio *full_bio = NULL; + struct dm_exception_table_lock lock; int error = 0; + dm_exception_table_lock_init(s, pe->e.old_chunk, &lock); + if (!success) { /* Read/write error - snapshot is unusable */ - mutex_lock(&s->lock); - __invalidate_snapshot(s, -EIO); + invalidate_snapshot(s, -EIO); error = 1; + + dm_exception_table_lock(&lock); goto out; } e = alloc_completed_exception(GFP_NOIO); if (!e) { - mutex_lock(&s->lock); - __invalidate_snapshot(s, -ENOMEM); + invalidate_snapshot(s, -ENOMEM); error = 1; + + dm_exception_table_lock(&lock); goto out; } *e = pe->e; - mutex_lock(&s->lock); + down_read(&s->lock); + dm_exception_table_lock(&lock); if (!s->valid) { + up_read(&s->lock); free_completed_exception(e); error = 1; + goto out; } @@ -1509,17 +1582,21 @@ static void pending_complete(void *context, int success) * merging can overwrite the chunk in origin. */ dm_insert_exception(&s->complete, e); + up_read(&s->lock); /* Wait for conflicting reads to drain */ if (__chunk_is_tracked(s, pe->e.old_chunk)) { - mutex_unlock(&s->lock); + dm_exception_table_unlock(&lock); __check_for_conflicting_io(s, pe->e.old_chunk); - mutex_lock(&s->lock); + dm_exception_table_lock(&lock); } out: /* Remove the in-flight exception from the list */ dm_remove_exception(&pe->e); + + dm_exception_table_unlock(&lock); + snapshot_bios = bio_list_get(&pe->snapshot_bios); origin_bios = bio_list_get(&pe->origin_bios); full_bio = pe->full_bio; @@ -1527,8 +1604,6 @@ static void pending_complete(void *context, int success) full_bio->bi_end_io = pe->full_bio_end_io; increment_pending_exceptions_done_count(); - mutex_unlock(&s->lock); - /* Submit any pending write bios */ if (error) { if (full_bio) @@ -1670,8 +1745,8 @@ __lookup_pending_exception(struct dm_snapshot *s, chunk_t chunk) /* * Inserts a pending exception into the pending table. * - * NOTE: a write lock must be held on snap->lock before calling - * this. + * NOTE: a write lock must be held on the chunk's pending exception table slot + * before calling this. */ static struct dm_snap_pending_exception * __insert_pending_exception(struct dm_snapshot *s, @@ -1683,12 +1758,15 @@ __insert_pending_exception(struct dm_snapshot *s, pe->started = 0; pe->full_bio = NULL; + spin_lock(&s->pe_allocation_lock); if (s->store->type->prepare_exception(s->store, &pe->e)) { + spin_unlock(&s->pe_allocation_lock); free_pending_exception(pe); return NULL; } pe->exception_sequence = s->exception_start_sequence++; + spin_unlock(&s->pe_allocation_lock); dm_insert_exception(&s->pending, &pe->e); @@ -1700,8 +1778,8 @@ __insert_pending_exception(struct dm_snapshot *s, * for this chunk, otherwise it allocates a new one and inserts * it into the pending table. * - * NOTE: a write lock must be held on snap->lock before calling - * this. + * NOTE: a write lock must be held on the chunk's pending exception table slot + * before calling this. */ static struct dm_snap_pending_exception * __find_pending_exception(struct dm_snapshot *s, @@ -1735,6 +1813,7 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio) int r = DM_MAPIO_REMAPPED; chunk_t chunk; struct dm_snap_pending_exception *pe = NULL; + struct dm_exception_table_lock lock; init_tracked_chunk(bio); @@ -1744,13 +1823,15 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio) } chunk = sector_to_chunk(s->store, bio->bi_iter.bi_sector); + dm_exception_table_lock_init(s, chunk, &lock); /* Full snapshots are not usable */ /* To get here the table must be live so s->active is always set. */ if (!s->valid) return DM_MAPIO_KILL; - mutex_lock(&s->lock); + down_read(&s->lock); + dm_exception_table_lock(&lock); if (!s->valid || (unlikely(s->snapshot_overflowed) && bio_data_dir(bio) == WRITE)) { @@ -1773,15 +1854,9 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio) if (bio_data_dir(bio) == WRITE) { pe = __lookup_pending_exception(s, chunk); if (!pe) { - mutex_unlock(&s->lock); + dm_exception_table_unlock(&lock); pe = alloc_pending_exception(s); - mutex_lock(&s->lock); - - if (!s->valid || s->snapshot_overflowed) { - free_pending_exception(pe); - r = DM_MAPIO_KILL; - goto out_unlock; - } + dm_exception_table_lock(&lock); e = dm_lookup_exception(&s->complete, chunk); if (e) { @@ -1792,13 +1867,22 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio) pe = __find_pending_exception(s, pe, chunk); if (!pe) { + dm_exception_table_unlock(&lock); + up_read(&s->lock); + + down_write(&s->lock); + if (s->store->userspace_supports_overflow) { - s->snapshot_overflowed = 1; - DMERR("Snapshot overflowed: Unable to allocate exception."); + if (s->valid && !s->snapshot_overflowed) { + s->snapshot_overflowed = 1; + DMERR("Snapshot overflowed: Unable to allocate exception."); + } } else __invalidate_snapshot(s, -ENOMEM); + up_write(&s->lock); + r = DM_MAPIO_KILL; - goto out_unlock; + goto out; } } @@ -1810,7 +1894,10 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio) bio->bi_iter.bi_size == (s->store->chunk_size << SECTOR_SHIFT)) { pe->started = 1; - mutex_unlock(&s->lock); + + dm_exception_table_unlock(&lock); + up_read(&s->lock); + start_full_bio(pe, bio); goto out; } @@ -1818,9 +1905,12 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio) bio_list_add(&pe->snapshot_bios, bio); if (!pe->started) { - /* this is protected by snap->lock */ + /* this is protected by the exception table lock */ pe->started = 1; - mutex_unlock(&s->lock); + + dm_exception_table_unlock(&lock); + up_read(&s->lock); + start_copy(pe); goto out; } @@ -1830,7 +1920,8 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio) } out_unlock: - mutex_unlock(&s->lock); + dm_exception_table_unlock(&lock); + up_read(&s->lock); out: return r; } @@ -1866,7 +1957,7 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio) chunk = sector_to_chunk(s->store, bio->bi_iter.bi_sector); - mutex_lock(&s->lock); + down_write(&s->lock); /* Full merging snapshots are redirected to the origin */ if (!s->valid) @@ -1897,12 +1988,12 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio) bio_set_dev(bio, s->origin->bdev); if (bio_data_dir(bio) == WRITE) { - mutex_unlock(&s->lock); + up_write(&s->lock); return do_origin(s->origin, bio); } out_unlock: - mutex_unlock(&s->lock); + up_write(&s->lock); return r; } @@ -1934,7 +2025,7 @@ static int snapshot_preresume(struct dm_target *ti) down_read(&_origins_lock); (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL); if (snap_src && snap_dest) { - mutex_lock(&snap_src->lock); + down_read(&snap_src->lock); if (s == snap_src) { DMERR("Unable to resume snapshot source until " "handover completes."); @@ -1944,7 +2035,7 @@ static int snapshot_preresume(struct dm_target *ti) "source is suspended."); r = -EINVAL; } - mutex_unlock(&snap_src->lock); + up_read(&snap_src->lock); } up_read(&_origins_lock); @@ -1990,11 +2081,11 @@ static void snapshot_resume(struct dm_target *ti) (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL); if (snap_src && snap_dest) { - mutex_lock(&snap_src->lock); - mutex_lock_nested(&snap_dest->lock, SINGLE_DEPTH_NESTING); + down_write(&snap_src->lock); + down_write_nested(&snap_dest->lock, SINGLE_DEPTH_NESTING); __handover_exceptions(snap_src, snap_dest); - mutex_unlock(&snap_dest->lock); - mutex_unlock(&snap_src->lock); + up_write(&snap_dest->lock); + up_write(&snap_src->lock); } up_read(&_origins_lock); @@ -2009,9 +2100,9 @@ static void snapshot_resume(struct dm_target *ti) /* Now we have correct chunk size, reregister */ reregister_snapshot(s); - mutex_lock(&s->lock); + down_write(&s->lock); s->active = 1; - mutex_unlock(&s->lock); + up_write(&s->lock); } static uint32_t get_origin_minimum_chunksize(struct block_device *bdev) @@ -2051,7 +2142,7 @@ static void snapshot_status(struct dm_target *ti, status_type_t type, switch (type) { case STATUSTYPE_INFO: - mutex_lock(&snap->lock); + down_write(&snap->lock); if (!snap->valid) DMEMIT("Invalid"); @@ -2076,7 +2167,7 @@ static void snapshot_status(struct dm_target *ti, status_type_t type, DMEMIT("Unknown"); } - mutex_unlock(&snap->lock); + up_write(&snap->lock); break; @@ -2131,6 +2222,7 @@ static int __origin_write(struct list_head *snapshots, sector_t sector, struct dm_snap_pending_exception *pe, *pe2; struct dm_snap_pending_exception *pe_to_start_now = NULL; struct dm_snap_pending_exception *pe_to_start_last = NULL; + struct dm_exception_table_lock lock; chunk_t chunk; /* Do all the snapshots on this origin */ @@ -2142,21 +2234,23 @@ static int __origin_write(struct list_head *snapshots, sector_t sector, if (dm_target_is_snapshot_merge(snap->ti)) continue; - mutex_lock(&snap->lock); - - /* Only deal with valid and active snapshots */ - if (!snap->valid || !snap->active) - goto next_snapshot; - /* Nothing to do if writing beyond end of snapshot */ if (sector >= dm_table_get_size(snap->ti->table)) - goto next_snapshot; + continue; /* * Remember, different snapshots can have * different chunk sizes. */ chunk = sector_to_chunk(snap->store, sector); + dm_exception_table_lock_init(snap, chunk, &lock); + + down_read(&snap->lock); + dm_exception_table_lock(&lock); + + /* Only deal with valid and active snapshots */ + if (!snap->valid || !snap->active) + goto next_snapshot; pe = __lookup_pending_exception(snap, chunk); if (!pe) { @@ -2169,14 +2263,9 @@ static int __origin_write(struct list_head *snapshots, sector_t sector, if (e) goto next_snapshot; - mutex_unlock(&snap->lock); + dm_exception_table_unlock(&lock); pe = alloc_pending_exception(snap); - mutex_lock(&snap->lock); - - if (!snap->valid) { - free_pending_exception(pe); - goto next_snapshot; - } + dm_exception_table_lock(&lock); pe2 = __lookup_pending_exception(snap, chunk); @@ -2189,8 +2278,11 @@ static int __origin_write(struct list_head *snapshots, sector_t sector, pe = __insert_pending_exception(snap, pe, chunk); if (!pe) { - __invalidate_snapshot(snap, -ENOMEM); - goto next_snapshot; + dm_exception_table_unlock(&lock); + up_read(&snap->lock); + + invalidate_snapshot(snap, -ENOMEM); + continue; } } else { free_pending_exception(pe); @@ -2221,7 +2313,8 @@ static int __origin_write(struct list_head *snapshots, sector_t sector, } next_snapshot: - mutex_unlock(&snap->lock); + dm_exception_table_unlock(&lock); + up_read(&snap->lock); if (pe_to_start_now) { start_copy(pe_to_start_now);