From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752648AbaFEEyp (ORCPT ); Thu, 5 Jun 2014 00:54:45 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:44015 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752707AbaFEEUy (ORCPT ); Thu, 5 Jun 2014 00:20:54 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Mikulas Patocka , Mike Snitzer , Rui Xiang Subject: [PATCH 3.4 099/214] dm snapshot: avoid snapshot space leak on crash Date: Wed, 4 Jun 2014 21:17:42 -0700 Message-Id: <20140605041653.013336882@linuxfoundation.org> X-Mailer: git-send-email 2.0.0 In-Reply-To: <20140605041639.638675216@linuxfoundation.org> References: <20140605041639.638675216@linuxfoundation.org> User-Agent: quilt/0.60-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Mikulas Patocka commit 230c83afdd9cd384348475bea1e14b80b3b6b1b8 upstream. There is a possible leak of snapshot space in case of crash. The reason for space leaking is that chunks in the snapshot device are allocated sequentially, but they are finished (and stored in the metadata) out of order, depending on the order in which copying finished. For example, supposed that the metadata contains the following records SUPERBLOCK METADATA (blocks 0 ... 250) DATA 0 DATA 1 DATA 2 ... DATA 250 Now suppose that you allocate 10 new data blocks 251-260. Suppose that copying of these blocks finish out of order (block 260 finished first and the block 251 finished last). Now, the snapshot device looks like this: SUPERBLOCK METADATA (blocks 0 ... 250, 260, 259, 258, 257, 256) DATA 0 DATA 1 DATA 2 ... DATA 250 DATA 251 DATA 252 DATA 253 DATA 254 DATA 255 METADATA (blocks 255, 254, 253, 252, 251) DATA 256 DATA 257 DATA 258 DATA 259 DATA 260 Now, if the machine crashes after writing the first metadata block but before writing the second metadata block, the space for areas DATA 250-255 is leaked, it contains no valid data and it will never be used in the future. This patch makes dm-snapshot complete exceptions in the same order they were allocated, thus fixing this bug. Note: when backporting this patch to the stable kernel, change the version field in the following way: * if version in the stable kernel is {1, 11, 1}, change it to {1, 12, 0} * if version in the stable kernel is {1, 10, 0} or {1, 10, 1}, change it to {1, 10, 2} Userspace reads the version to determine if the bug was fixed, so the version change is needed. Signed-off-by: Mikulas Patocka Signed-off-by: Mike Snitzer [xr: Backported to 3.4: adjust version] Signed-off-by: Rui Xiang Signed-off-by: Greg Kroah-Hartman --- drivers/md/dm-snap.c | 71 +++++++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 64 insertions(+), 7 deletions(-) --- a/drivers/md/dm-snap.c +++ b/drivers/md/dm-snap.c @@ -66,6 +66,18 @@ struct dm_snapshot { atomic_t pending_exceptions_count; + /* Protected by "lock" */ + sector_t exception_start_sequence; + + /* Protected by kcopyd single-threaded callback */ + sector_t exception_complete_sequence; + + /* + * A list of pending exceptions that completed out of order. + * Protected by kcopyd single-threaded callback. + */ + struct list_head out_of_order_list; + mempool_t *pending_pool; struct dm_exception_table pending; @@ -171,6 +183,14 @@ struct dm_snap_pending_exception { */ int started; + /* There was copying error. */ + int copy_error; + + /* A sequence number, it is used for in-order completion. */ + sector_t exception_sequence; + + struct list_head out_of_order_entry; + /* * For writing a complete chunk, bypassing the copy. */ @@ -1090,6 +1110,9 @@ static int snapshot_ctr(struct dm_target s->valid = 1; s->active = 0; atomic_set(&s->pending_exceptions_count, 0); + s->exception_start_sequence = 0; + s->exception_complete_sequence = 0; + INIT_LIST_HEAD(&s->out_of_order_list); init_rwsem(&s->lock); INIT_LIST_HEAD(&s->list); spin_lock_init(&s->pe_lock); @@ -1448,6 +1471,19 @@ static void commit_callback(void *contex pending_complete(pe, success); } +static void complete_exception(struct dm_snap_pending_exception *pe) +{ + struct dm_snapshot *s = pe->snap; + + if (unlikely(pe->copy_error)) + pending_complete(pe, 0); + + else + /* Update the metadata if we are persistent */ + s->store->type->commit_exception(s->store, &pe->e, + commit_callback, pe); +} + /* * Called when the copy I/O has finished. kcopyd actually runs * this code so don't block. @@ -1457,13 +1493,32 @@ static void copy_callback(int read_err, struct dm_snap_pending_exception *pe = context; struct dm_snapshot *s = pe->snap; - if (read_err || write_err) - pending_complete(pe, 0); + pe->copy_error = read_err || write_err; - else - /* Update the metadata if we are persistent */ - s->store->type->commit_exception(s->store, &pe->e, - commit_callback, pe); + if (pe->exception_sequence == s->exception_complete_sequence) { + s->exception_complete_sequence++; + complete_exception(pe); + + while (!list_empty(&s->out_of_order_list)) { + pe = list_entry(s->out_of_order_list.next, + struct dm_snap_pending_exception, out_of_order_entry); + if (pe->exception_sequence != s->exception_complete_sequence) + break; + s->exception_complete_sequence++; + list_del(&pe->out_of_order_entry); + complete_exception(pe); + } + } else { + struct list_head *lh; + struct dm_snap_pending_exception *pe2; + + list_for_each_prev(lh, &s->out_of_order_list) { + pe2 = list_entry(lh, struct dm_snap_pending_exception, out_of_order_entry); + if (pe2->exception_sequence < pe->exception_sequence) + break; + } + list_add(&pe->out_of_order_entry, lh); + } } /* @@ -1558,6 +1613,8 @@ __find_pending_exception(struct dm_snaps return NULL; } + pe->exception_sequence = s->exception_start_sequence++; + dm_insert_exception(&s->pending, &pe->e); return pe; @@ -2200,7 +2257,7 @@ static struct target_type origin_target static struct target_type snapshot_target = { .name = "snapshot", - .version = {1, 10, 0}, + .version = {1, 10, 2}, .module = THIS_MODULE, .ctr = snapshot_ctr, .dtr = snapshot_dtr,