[PATCH 0/2] Fix error handling in preallocate_co()

[PATCH 0/2] Fix error handling in preallocate_co()

[Alberto Garcia]

This is a follow-up to "Fix removal of list members from
BDRVQcow2State.cluster_allocs":

   https://lists.gnu.org/archive/html/qemu-block/2020-09/msg00247.html

However the patches themselves are independent and can be applied
separately.

Regards,

Berto

Alberto Garcia (2):
  qcow2: Handle QCowL2Meta on error in preallocate_co()
  qcow2: Make qcow2_free_any_clusters() free only one cluster

 block/qcow2.h          |  4 ++--
 block/qcow2-cluster.c  |  6 +++---
 block/qcow2-refcount.c |  8 ++++----
 block/qcow2.c          | 40 +++++++++++++++++-----------------------
 4 files changed, 26 insertions(+), 32 deletions(-)

-- 
2.20.1

[PATCH 1/2] qcow2: Handle QCowL2Meta on error in preallocate_co()

[Alberto Garcia]

If qcow2_alloc_cluster_offset() or qcow2_alloc_cluster_link_l2() fail
then this function simply returns the error code, potentially leaking
the QCowL2Meta structure and leaving stale items in s->cluster_allocs.

A second problem is that this function calls qcow2_free_any_clusters()
on failure but passing a host cluster offset instead of an L2 entry.
Luckily for normal uncompressed clusters a raw offset also works like
a valid L2 entry so it works just the same, but we should be using
qcow2_free_clusters() instead.

This patch fixes both problems by using qcow2_handle_l2meta().

Signed-off-by: Alberto Garcia <berto@igalia.com>
---
 block/qcow2.c | 40 +++++++++++++++++-----------------------
 1 file changed, 17 insertions(+), 23 deletions(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index da56b1a4df..eeb125c697 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2102,7 +2102,6 @@ static coroutine_fn int qcow2_handle_l2meta(BlockDriverState *bs,
         QCowL2Meta *next;
 
         if (link_l2) {
-            assert(!l2meta->prealloc);
             ret = qcow2_alloc_cluster_link_l2(bs, l2meta);
             if (ret) {
                 goto out;
@@ -3126,7 +3125,7 @@ static int coroutine_fn preallocate_co(BlockDriverState *bs, uint64_t offset,
     int64_t file_length;
     unsigned int cur_bytes;
     int ret;
-    QCowL2Meta *meta;
+    QCowL2Meta *meta = NULL, *m;
 
     assert(offset <= new_length);
     bytes = new_length - offset;
@@ -3137,27 +3136,17 @@ static int coroutine_fn preallocate_co(BlockDriverState *bs, uint64_t offset,
                                          &host_offset, &meta);
         if (ret < 0) {
             error_setg_errno(errp, -ret, "Allocating clusters failed");
-            return ret;
+            goto out;
         }
 
-        while (meta) {
-            QCowL2Meta *next = meta->next;
-            meta->prealloc = true;
-
-            ret = qcow2_alloc_cluster_link_l2(bs, meta);
-            if (ret < 0) {
-                error_setg_errno(errp, -ret, "Mapping clusters failed");
-                qcow2_free_any_clusters(bs, meta->alloc_offset,
-                                        meta->nb_clusters, QCOW2_DISCARD_NEVER);
-                return ret;
-            }
-
-            /* There are no dependent requests, but we need to remove our
-             * request from the list of in-flight requests */
-            QLIST_REMOVE(meta, next_in_flight);
+        for (m = meta; m != NULL; m = m->next) {
+            m->prealloc = true;
+        }
 
-            g_free(meta);
-            meta = next;
+        ret = qcow2_handle_l2meta(bs, &meta, true);
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "Mapping clusters failed");
+            goto out;
         }
 
         /* TODO Preallocate data if requested */
@@ -3174,7 +3163,8 @@ static int coroutine_fn preallocate_co(BlockDriverState *bs, uint64_t offset,
     file_length = bdrv_getlength(s->data_file->bs);
     if (file_length < 0) {
         error_setg_errno(errp, -file_length, "Could not get file size");
-        return file_length;
+        ret = file_length;
+        goto out;
     }
 
     if (host_offset + cur_bytes > file_length) {
@@ -3184,11 +3174,15 @@ static int coroutine_fn preallocate_co(BlockDriverState *bs, uint64_t offset,
         ret = bdrv_co_truncate(s->data_file, host_offset + cur_bytes, false,
                                mode, 0, errp);
         if (ret < 0) {
-            return ret;
+            goto out;
         }
     }
 
-    return 0;
+    ret = 0;
+
+out:
+    qcow2_handle_l2meta(bs, &meta, false);
+    return ret;
 }
 
 /* qcow2_refcount_metadata_size:
-- 
2.20.1

[PATCH 2/2] qcow2: Make qcow2_free_any_clusters() free only one cluster

[Alberto Garcia]

This function takes an L2 entry and a number of clusters to free.
Although in principle it can free any type of cluster (using the L2
entry to determine its type) in practice the API is broken because
compressed clusters have a variable size and there is no way to free
more than one without having the L2 entry of each one of them.

The good news all callers are passing nb_clusters=1 so we can simply
get rid of that parameter.

Signed-off-by: Alberto Garcia <berto@igalia.com>
---
 block/qcow2.h          | 4 ++--
 block/qcow2-cluster.c  | 6 +++---
 block/qcow2-refcount.c | 8 ++++----
 3 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/block/qcow2.h b/block/qcow2.h
index 065ec3df0b..bb6358121d 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -855,8 +855,8 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size);
 void qcow2_free_clusters(BlockDriverState *bs,
                           int64_t offset, int64_t size,
                           enum qcow2_discard_type type);
-void qcow2_free_any_clusters(BlockDriverState *bs, uint64_t l2_entry,
-                             int nb_clusters, enum qcow2_discard_type type);
+void qcow2_free_any_cluster(BlockDriverState *bs, uint64_t l2_entry,
+                            enum qcow2_discard_type type);
 
 int qcow2_update_snapshot_refcount(BlockDriverState *bs,
     int64_t l1_table_offset, int l1_size, int addend);
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 996b3314f4..89c561e4c0 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -1096,7 +1096,7 @@ int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m)
      */
     if (!m->keep_old_clusters && j != 0) {
         for (i = 0; i < j; i++) {
-            qcow2_free_any_clusters(bs, old_cluster[i], 1, QCOW2_DISCARD_NEVER);
+            qcow2_free_any_cluster(bs, old_cluster[i], QCOW2_DISCARD_NEVER);
         }
     }
 
@@ -1911,7 +1911,7 @@ static int discard_in_l2_slice(BlockDriverState *bs, uint64_t offset,
             set_l2_bitmap(s, l2_slice, l2_index + i, new_l2_bitmap);
         }
         /* Then decrease the refcount */
-        qcow2_free_any_clusters(bs, old_l2_entry, 1, type);
+        qcow2_free_any_cluster(bs, old_l2_entry, type);
     }
 
     qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
@@ -2003,7 +2003,7 @@ static int zero_in_l2_slice(BlockDriverState *bs, uint64_t offset,
 
         qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
         if (unmap) {
-            qcow2_free_any_clusters(bs, old_l2_entry, 1, QCOW2_DISCARD_REQUEST);
+            qcow2_free_any_cluster(bs, old_l2_entry, QCOW2_DISCARD_REQUEST);
         }
         set_l2_entry(s, l2_slice, l2_index + i, new_l2_entry);
         if (has_subclusters(s)) {
diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index aae52607eb..fc9bb2258f 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -1156,8 +1156,8 @@ void qcow2_free_clusters(BlockDriverState *bs,
  * Free a cluster using its L2 entry (handles clusters of all types, e.g.
  * normal cluster, compressed cluster, etc.)
  */
-void qcow2_free_any_clusters(BlockDriverState *bs, uint64_t l2_entry,
-                             int nb_clusters, enum qcow2_discard_type type)
+void qcow2_free_any_cluster(BlockDriverState *bs, uint64_t l2_entry,
+                            enum qcow2_discard_type type)
 {
     BDRVQcow2State *s = bs->opaque;
     QCow2ClusterType ctype = qcow2_get_cluster_type(bs, l2_entry);
@@ -1168,7 +1168,7 @@ void qcow2_free_any_clusters(BlockDriverState *bs, uint64_t l2_entry,
              ctype == QCOW2_CLUSTER_ZERO_ALLOC))
         {
             bdrv_pdiscard(s->data_file, l2_entry & L2E_OFFSET_MASK,
-                          nb_clusters << s->cluster_bits);
+                          s->cluster_size);
         }
         return;
     }
@@ -1191,7 +1191,7 @@ void qcow2_free_any_clusters(BlockDriverState *bs, uint64_t l2_entry,
                                     l2_entry & L2E_OFFSET_MASK);
         } else {
             qcow2_free_clusters(bs, l2_entry & L2E_OFFSET_MASK,
-                                nb_clusters << s->cluster_bits, type);
+                                s->cluster_size, type);
         }
         break;
     case QCOW2_CLUSTER_ZERO_PLAIN:
-- 
2.20.1

Re: [PATCH 0/2] Fix error handling in preallocate_co()

[Kevin Wolf]

Am 08.09.2020 um 16:08 hat Alberto Garcia geschrieben:
> This is a follow-up to "Fix removal of list members from
> BDRVQcow2State.cluster_allocs":
> 
>    https://lists.gnu.org/archive/html/qemu-block/2020-09/msg00247.html
> 
> However the patches themselves are independent and can be applied
> separately.

Reviewed-by: Kevin Wolf <kwolf@redhat.com>

Re: [PATCH 0/2] Fix error handling in preallocate_co()

[Max Reitz]

[-- Attachment #1.1: Type: text/plain, Size: 834 bytes --]

On 08.09.20 16:08, Alberto Garcia wrote:
> This is a follow-up to "Fix removal of list members from
> BDRVQcow2State.cluster_allocs":
> 
>    https://lists.gnu.org/archive/html/qemu-block/2020-09/msg00247.html
> 
> However the patches themselves are independent and can be applied
> separately.
> 
> Regards,
> 
> Berto
> 
> Alberto Garcia (2):
>   qcow2: Handle QCowL2Meta on error in preallocate_co()
>   qcow2: Make qcow2_free_any_clusters() free only one cluster
> 
>  block/qcow2.h          |  4 ++--
>  block/qcow2-cluster.c  |  6 +++---
>  block/qcow2-refcount.c |  8 ++++----
>  block/qcow2.c          | 40 +++++++++++++++++-----------------------
>  4 files changed, 26 insertions(+), 32 deletions(-)

Thanks, applied to my block branch:

https://git.xanclic.moe/XanClic/qemu/commits/branch/block


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