[29/55] blockjob: update nodes head while removing all bdrv

Commit Message

Michael Roth Nov. 5, 2019, 8:52 p.m. UTC

From: Sergio Lopez <[e-mail]>

block_job_remove_all_bdrv() iterates through job->nodes, calling
bdrv_root_unref_child() for each entry. The call to the latter may
reach child_job_[can_]set_aio_ctx(), which will also attempt to
traverse job->nodes, potentially finding entries that where freed
on previous iterations.

To avoid this situation, update job->nodes head on each iteration to
ensure that already freed entries are no longer linked to the list.

RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1746631
Signed-off-by: Sergio Lopez <[e-mail]>
Cc: [e-mail]
Signed-off-by: Max Reitz <[e-mail]>
Message-id: [e-mail]
Reviewed-by: Sergio Lopez <[e-mail]>
Signed-off-by: Max Reitz <[e-mail]>
(cherry picked from commit d876bf676f5e7c6aa9ac64555e48cba8734ecb2f)
Signed-off-by: Michael Roth <[e-mail]>
---
 blockjob.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

Patch

diff --git a/blockjob.c b/blockjob.c
index 20b7f557da..74abb97bfd 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -186,14 +186,23 @@  static const BdrvChildRole child_job = {
 
 void block_job_remove_all_bdrv(BlockJob *job)
 {
-    GSList *l;
-    for (l = job->nodes; l; l = l->next) {
+    /*
+     * bdrv_root_unref_child() may reach child_job_[can_]set_aio_ctx(),
+     * which will also traverse job->nodes, so consume the list one by
+     * one to make sure that such a concurrent access does not attempt
+     * to process an already freed BdrvChild.
+     */
+    while (job->nodes) {
+        GSList *l = job->nodes;
         BdrvChild *c = l->data;
+
+        job->nodes = l->next;
+
         bdrv_op_unblock_all(c->bs, job->blocker);
         bdrv_root_unref_child(c);
+
+        g_slist_free_1(l);
     }
-    g_slist_free(job->nodes);
-    job->nodes = NULL;
 }
 
 bool block_job_has_bdrv(BlockJob *job, BlockDriverState *bs)