[Qemu-devel] [PATCH v3] block: Fix bdrv_next() memory leak

[Qemu-devel] [PATCH v3] block: Fix bdrv_next() memory leak

[Kevin Wolf]

The bdrv_next() users all leaked the BdrvNextIterator after completing
the iteration. Simply changing bdrv_next() to free the iterator before
returning NULL at the end of list doesn't work because some callers exit
the loop before looking at all BDSes.

This patch moves the BdrvNextIterator from the heap to the stack of
the caller and switches to a bdrv_first()/bdrv_next() interface for
initialising the iterator.

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

v3:
- block/snapshot.c: With the change to a for loop, bdrv_next() is executed
  unconditionally, even if the exit condition is true. We now need to
  explicitly jump out of the loop if bs should stay the same.

 block.c               | 18 ++++++++---------
 block/block-backend.c | 41 +++++++++++++++++---------------------
 block/io.c            | 10 ++++------
 block/snapshot.c      | 55 ++++++++++++++++++++++++++++++++++++++-------------
 blockdev.c            |  4 ++--
 include/block/block.h | 15 ++++++++++++--
 migration/block.c     |  4 ++--
 monitor.c             |  4 ++--
 qmp.c                 |  5 ++---
 9 files changed, 92 insertions(+), 64 deletions(-)

diff --git a/block.c b/block.c
index 1205ef8..d287771 100644
--- a/block.c
+++ b/block.c
@@ -3195,9 +3195,9 @@ void bdrv_invalidate_cache_all(Error **errp)
 {
     BlockDriverState *bs;
     Error *local_err = NULL;
-    BdrvNextIterator *it = NULL;
+    BdrvNextIterator it;
 
-    while ((it = bdrv_next(it, &bs)) != NULL) {
+    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         AioContext *aio_context = bdrv_get_aio_context(bs);
 
         aio_context_acquire(aio_context);
@@ -3239,11 +3239,11 @@ static int bdrv_inactivate_recurse(BlockDriverState *bs,
 int bdrv_inactivate_all(void)
 {
     BlockDriverState *bs = NULL;
-    BdrvNextIterator *it = NULL;
+    BdrvNextIterator it;
     int ret = 0;
     int pass;
 
-    while ((it = bdrv_next(it, &bs)) != NULL) {
+    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         aio_context_acquire(bdrv_get_aio_context(bs));
     }
 
@@ -3252,8 +3252,7 @@ int bdrv_inactivate_all(void)
      * the second pass sets the BDRV_O_INACTIVE flag so that no further write
      * is allowed. */
     for (pass = 0; pass < 2; pass++) {
-        it = NULL;
-        while ((it = bdrv_next(it, &bs)) != NULL) {
+        for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
             ret = bdrv_inactivate_recurse(bs, pass);
             if (ret < 0) {
                 goto out;
@@ -3262,8 +3261,7 @@ int bdrv_inactivate_all(void)
     }
 
 out:
-    it = NULL;
-    while ((it = bdrv_next(it, &bs)) != NULL) {
+    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         aio_context_release(bdrv_get_aio_context(bs));
     }
 
@@ -3753,10 +3751,10 @@ bool bdrv_recurse_is_first_non_filter(BlockDriverState *bs,
 bool bdrv_is_first_non_filter(BlockDriverState *candidate)
 {
     BlockDriverState *bs;
-    BdrvNextIterator *it = NULL;
+    BdrvNextIterator it;
 
     /* walk down the bs forest recursively */
-    while ((it = bdrv_next(it, &bs)) != NULL) {
+    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         bool perm;
 
         /* try to recurse in this top level bs */
diff --git a/block/block-backend.c b/block/block-backend.c
index 6928d61..9f306f8 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -286,25 +286,11 @@ BlockBackend *blk_next(BlockBackend *blk)
                : QTAILQ_FIRST(&monitor_block_backends);
 }
 
-struct BdrvNextIterator {
-    enum {
-        BDRV_NEXT_BACKEND_ROOTS,
-        BDRV_NEXT_MONITOR_OWNED,
-    } phase;
-    BlockBackend *blk;
-    BlockDriverState *bs;
-};
-
 /* Iterates over all top-level BlockDriverStates, i.e. BDSs that are owned by
  * the monitor or attached to a BlockBackend */
-BdrvNextIterator *bdrv_next(BdrvNextIterator *it, BlockDriverState **bs)
+BlockDriverState *bdrv_next(BdrvNextIterator *it)
 {
-    if (!it) {
-        it = g_new(BdrvNextIterator, 1);
-        *it = (BdrvNextIterator) {
-            .phase = BDRV_NEXT_BACKEND_ROOTS,
-        };
-    }
+    BlockDriverState *bs;
 
     /* First, return all root nodes of BlockBackends. In order to avoid
      * returning a BDS twice when multiple BBs refer to it, we only return it
@@ -312,11 +298,11 @@ BdrvNextIterator *bdrv_next(BdrvNextIterator *it, BlockDriverState **bs)
     if (it->phase == BDRV_NEXT_BACKEND_ROOTS) {
         do {
             it->blk = blk_all_next(it->blk);
-            *bs = it->blk ? blk_bs(it->blk) : NULL;
-        } while (it->blk && (*bs == NULL || bdrv_first_blk(*bs) != it->blk));
+            bs = it->blk ? blk_bs(it->blk) : NULL;
+        } while (it->blk && (bs == NULL || bdrv_first_blk(bs) != it->blk));
 
-        if (*bs) {
-            return it;
+        if (bs) {
+            return bs;
         }
         it->phase = BDRV_NEXT_MONITOR_OWNED;
     }
@@ -326,10 +312,19 @@ BdrvNextIterator *bdrv_next(BdrvNextIterator *it, BlockDriverState **bs)
      * by the above block already */
     do {
         it->bs = bdrv_next_monitor_owned(it->bs);
-        *bs = it->bs;
-    } while (*bs && bdrv_has_blk(*bs));
+        bs = it->bs;
+    } while (bs && bdrv_has_blk(bs));
+
+    return bs;
+}
+
+BlockDriverState *bdrv_first(BdrvNextIterator *it)
+{
+    *it = (BdrvNextIterator) {
+        .phase = BDRV_NEXT_BACKEND_ROOTS,
+    };
 
-    return *bs ? it : NULL;
+    return bdrv_next(it);
 }
 
 /*
diff --git a/block/io.c b/block/io.c
index 60a6bd8..2a28d63 100644
--- a/block/io.c
+++ b/block/io.c
@@ -271,10 +271,10 @@ void bdrv_drain_all(void)
     /* Always run first iteration so any pending completion BHs run */
     bool busy = true;
     BlockDriverState *bs;
-    BdrvNextIterator *it = NULL;
+    BdrvNextIterator it;
     GSList *aio_ctxs = NULL, *ctx;
 
-    while ((it = bdrv_next(it, &bs))) {
+    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         AioContext *aio_context = bdrv_get_aio_context(bs);
 
         aio_context_acquire(aio_context);
@@ -302,10 +302,9 @@ void bdrv_drain_all(void)
 
         for (ctx = aio_ctxs; ctx != NULL; ctx = ctx->next) {
             AioContext *aio_context = ctx->data;
-            it = NULL;
 
             aio_context_acquire(aio_context);
-            while ((it = bdrv_next(it, &bs))) {
+            for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
                 if (aio_context == bdrv_get_aio_context(bs)) {
                     if (bdrv_requests_pending(bs)) {
                         busy = true;
@@ -318,8 +317,7 @@ void bdrv_drain_all(void)
         }
     }
 
-    it = NULL;
-    while ((it = bdrv_next(it, &bs))) {
+    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         AioContext *aio_context = bdrv_get_aio_context(bs);
 
         aio_context_acquire(aio_context);
diff --git a/block/snapshot.c b/block/snapshot.c
index 3917ec5..6e6e34f 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -374,9 +374,9 @@ bool bdrv_all_can_snapshot(BlockDriverState **first_bad_bs)
 {
     bool ok = true;
     BlockDriverState *bs;
-    BdrvNextIterator *it = NULL;
+    BdrvNextIterator it;
 
-    while (ok && (it = bdrv_next(it, &bs))) {
+    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         AioContext *ctx = bdrv_get_aio_context(bs);
 
         aio_context_acquire(ctx);
@@ -384,8 +384,12 @@ bool bdrv_all_can_snapshot(BlockDriverState **first_bad_bs)
             ok = bdrv_can_snapshot(bs);
         }
         aio_context_release(ctx);
+        if (!ok) {
+            goto fail;
+        }
     }
 
+fail:
     *first_bad_bs = bs;
     return ok;
 }
@@ -395,20 +399,27 @@ int bdrv_all_delete_snapshot(const char *name, BlockDriverState **first_bad_bs,
 {
     int ret = 0;
     BlockDriverState *bs;
-    BdrvNextIterator *it = NULL;
+    BdrvNextIterator it;
     QEMUSnapshotInfo sn1, *snapshot = &sn1;
 
-    while (ret == 0 && (it = bdrv_next(it, &bs))) {
+    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         AioContext *ctx = bdrv_get_aio_context(bs);
 
         aio_context_acquire(ctx);
         if (bdrv_can_snapshot(bs) &&
                 bdrv_snapshot_find(bs, snapshot, name) >= 0) {
             ret = bdrv_snapshot_delete_by_id_or_name(bs, name, err);
+            if (ret < 0) {
+                goto fail;
+            }
         }
         aio_context_release(ctx);
+        if (ret < 0) {
+            goto fail;
+        }
     }
 
+fail:
     *first_bad_bs = bs;
     return ret;
 }
@@ -418,9 +429,9 @@ int bdrv_all_goto_snapshot(const char *name, BlockDriverState **first_bad_bs)
 {
     int err = 0;
     BlockDriverState *bs;
-    BdrvNextIterator *it = NULL;
+    BdrvNextIterator it;
 
-    while (err == 0 && (it = bdrv_next(it, &bs))) {
+    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         AioContext *ctx = bdrv_get_aio_context(bs);
 
         aio_context_acquire(ctx);
@@ -428,8 +439,12 @@ int bdrv_all_goto_snapshot(const char *name, BlockDriverState **first_bad_bs)
             err = bdrv_snapshot_goto(bs, name);
         }
         aio_context_release(ctx);
+        if (err < 0) {
+            goto fail;
+        }
     }
 
+fail:
     *first_bad_bs = bs;
     return err;
 }
@@ -439,9 +454,9 @@ int bdrv_all_find_snapshot(const char *name, BlockDriverState **first_bad_bs)
     QEMUSnapshotInfo sn;
     int err = 0;
     BlockDriverState *bs;
-    BdrvNextIterator *it = NULL;
+    BdrvNextIterator it;
 
-    while (err == 0 && (it = bdrv_next(it, &bs))) {
+    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         AioContext *ctx = bdrv_get_aio_context(bs);
 
         aio_context_acquire(ctx);
@@ -449,8 +464,12 @@ int bdrv_all_find_snapshot(const char *name, BlockDriverState **first_bad_bs)
             err = bdrv_snapshot_find(bs, &sn, name);
         }
         aio_context_release(ctx);
+        if (err < 0) {
+            goto fail;
+        }
     }
 
+fail:
     *first_bad_bs = bs;
     return err;
 }
@@ -462,9 +481,9 @@ int bdrv_all_create_snapshot(QEMUSnapshotInfo *sn,
 {
     int err = 0;
     BlockDriverState *bs;
-    BdrvNextIterator *it = NULL;
+    BdrvNextIterator it;
 
-    while (err == 0 && (it = bdrv_next(it, &bs))) {
+    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         AioContext *ctx = bdrv_get_aio_context(bs);
 
         aio_context_acquire(ctx);
@@ -476,24 +495,32 @@ int bdrv_all_create_snapshot(QEMUSnapshotInfo *sn,
             err = bdrv_snapshot_create(bs, sn);
         }
         aio_context_release(ctx);
+        if (err < 0) {
+            goto fail;
+        }
     }
 
+fail:
     *first_bad_bs = bs;
     return err;
 }
 
 BlockDriverState *bdrv_all_find_vmstate_bs(void)
 {
-    bool not_found = true;
     BlockDriverState *bs;
-    BdrvNextIterator *it = NULL;
+    BdrvNextIterator it;
 
-    while (not_found && (it = bdrv_next(it, &bs))) {
+    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         AioContext *ctx = bdrv_get_aio_context(bs);
+        bool found;
 
         aio_context_acquire(ctx);
-        not_found = !bdrv_can_snapshot(bs);
+        found = bdrv_can_snapshot(bs);
         aio_context_release(ctx);
+
+        if (found) {
+            break;
+        }
     }
     return bs;
 }
diff --git a/blockdev.c b/blockdev.c
index 40e4e6f..0e37e09 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -4164,9 +4164,9 @@ BlockJobInfoList *qmp_query_block_jobs(Error **errp)
 {
     BlockJobInfoList *head = NULL, **p_next = &head;
     BlockDriverState *bs;
-    BdrvNextIterator *it = NULL;
+    BdrvNextIterator it;
 
-    while ((it = bdrv_next(it, &bs))) {
+    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         AioContext *aio_context = bdrv_get_aio_context(bs);
 
         aio_context_acquire(aio_context);
diff --git a/include/block/block.h b/include/block/block.h
index a8c15e3..770ca26 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -17,7 +17,6 @@ typedef struct BlockJob BlockJob;
 typedef struct BdrvChild BdrvChild;
 typedef struct BdrvChildRole BdrvChildRole;
 typedef struct BlockJobTxn BlockJobTxn;
-typedef struct BdrvNextIterator BdrvNextIterator;
 
 typedef struct BlockDriverInfo {
     /* in bytes, 0 if irrelevant */
@@ -402,7 +401,19 @@ BlockDriverState *bdrv_lookup_bs(const char *device,
                                  Error **errp);
 bool bdrv_chain_contains(BlockDriverState *top, BlockDriverState *base);
 BlockDriverState *bdrv_next_node(BlockDriverState *bs);
-BdrvNextIterator *bdrv_next(BdrvNextIterator *it, BlockDriverState **bs);
+
+typedef struct BdrvNextIterator {
+    enum {
+        BDRV_NEXT_BACKEND_ROOTS,
+        BDRV_NEXT_MONITOR_OWNED,
+    } phase;
+    BlockBackend *blk;
+    BlockDriverState *bs;
+} BdrvNextIterator;
+
+BlockDriverState *bdrv_first(BdrvNextIterator *it);
+BlockDriverState *bdrv_next(BdrvNextIterator *it);
+
 BlockDriverState *bdrv_next_monitor_owned(BlockDriverState *bs);
 int bdrv_is_encrypted(BlockDriverState *bs);
 int bdrv_key_required(BlockDriverState *bs);
diff --git a/migration/block.c b/migration/block.c
index a7a76a0..e0628d1 100644
--- a/migration/block.c
+++ b/migration/block.c
@@ -383,7 +383,7 @@ static void init_blk_migration(QEMUFile *f)
     BlockDriverState *bs;
     BlkMigDevState *bmds;
     int64_t sectors;
-    BdrvNextIterator *it = NULL;
+    BdrvNextIterator it;
 
     block_mig_state.submitted = 0;
     block_mig_state.read_done = 0;
@@ -394,7 +394,7 @@ static void init_blk_migration(QEMUFile *f)
     block_mig_state.zero_blocks = migrate_zero_blocks();
 
 
-    while ((it = bdrv_next(it, &bs))) {
+    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         if (bdrv_is_read_only(bs)) {
             continue;
         }
diff --git a/monitor.c b/monitor.c
index 2c87244..6c4bac7 100644
--- a/monitor.c
+++ b/monitor.c
@@ -3428,12 +3428,12 @@ static void vm_completion(ReadLineState *rs, const char *str)
 {
     size_t len;
     BlockDriverState *bs;
-    BdrvNextIterator *it = NULL;
+    BdrvNextIterator it;
 
     len = strlen(str);
     readline_set_completion_index(rs, len);
 
-    while ((it = bdrv_next(it, &bs))) {
+    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         SnapshotInfoList *snapshots, *snapshot;
         AioContext *ctx = bdrv_get_aio_context(bs);
         bool ok = false;
diff --git a/qmp.c b/qmp.c
index 8f8ae3a..3165f87 100644
--- a/qmp.c
+++ b/qmp.c
@@ -181,7 +181,7 @@ void qmp_cont(Error **errp)
     Error *local_err = NULL;
     BlockBackend *blk;
     BlockDriverState *bs;
-    BdrvNextIterator *it;
+    BdrvNextIterator it;
 
     /* if there is a dump in background, we should wait until the dump
      * finished */
@@ -201,8 +201,7 @@ void qmp_cont(Error **errp)
         blk_iostatus_reset(blk);
     }
 
-    it = NULL;
-    while ((it = bdrv_next(it, &bs))) {
+    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         bdrv_add_key(bs, NULL, &local_err);
         if (local_err) {
             error_propagate(errp, local_err);
-- 
1.8.3.1

Re: [Qemu-devel] [PATCH v3] block: Fix bdrv_next() memory leak

[Fam Zheng]

On Fri, 05/20 19:17, Kevin Wolf wrote:
> The bdrv_next() users all leaked the BdrvNextIterator after completing
> the iteration. Simply changing bdrv_next() to free the iterator before
> returning NULL at the end of list doesn't work because some callers exit
> the loop before looking at all BDSes.
> 
> This patch moves the BdrvNextIterator from the heap to the stack of
> the caller and switches to a bdrv_first()/bdrv_next() interface for
> initialising the iterator.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Reviewed-by: Fam Zheng <famz@redhat.com>

Re: [Qemu-devel] [PATCH v3] block: Fix bdrv_next() memory leak

[Kevin Wolf]

Am 20.05.2016 um 19:17 hat Kevin Wolf geschrieben:
> The bdrv_next() users all leaked the BdrvNextIterator after completing
> the iteration. Simply changing bdrv_next() to free the iterator before
> returning NULL at the end of list doesn't work because some callers exit
> the loop before looking at all BDSes.
> 
> This patch moves the BdrvNextIterator from the heap to the stack of
> the caller and switches to a bdrv_first()/bdrv_next() interface for
> initialising the iterator.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Applied to the block branch.

Kevin