@@ -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;
@@ -173,6 +185,14 @@ 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.
*/
@@ -1094,6 +1114,9 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
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);
@@ -1443,6 +1466,19 @@ static void commit_callback(void *context, int success)
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.
@@ -1452,13 +1488,32 @@ static void copy_callback(int read_err, unsigned long write_err, void *context)
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);
+ }
}
/*
@@ -1553,6 +1608,8 @@ __find_pending_exception(struct dm_snapshot *s,
return NULL;
}
+ pe->exception_sequence = s->exception_start_sequence++;
+
dm_insert_exception(&s->pending, &pe->e);
return pe;
@@ -2192,7 +2249,7 @@ static struct target_type origin_target = {
static struct target_type snapshot_target = {
.name = "snapshot",
- .version = {1, 11, 1},
+ .version = {1, 12, 0},
.module = THIS_MODULE,
.ctr = snapshot_ctr,
.dtr = snapshot_dtr,
This is a note to let you know that I have just added a patch titled dm snapshot: avoid snapshot space leak on crash to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.11.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ------ From 6c01c8c5bc2c7ead73e0a5c61a5057540c03e022 Mon Sep 17 00:00:00 2001 From: Mikulas Patocka <mpatocka@redhat.com> Date: Fri, 29 Nov 2013 18:13:37 -0500 Subject: dm snapshot: avoid snapshot space leak on crash 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 <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- drivers/md/dm-snap.c | 71 ++++++++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 64 insertions(+), 7 deletions(-) -- 1.8.3.2