[Qemu-devel] [PATCH] Allow nested qemu_bh_poll() after BH deletion

[Qemu-devel] [PATCH] Allow nested qemu_bh_poll() after BH deletion

[Kevin Wolf]

Without this, qemu segfaults when a BH handler first deletes its BH and
then calls another function which involves a nested qemu_bh_poll() call.

This can be reproduced by generating an I/O error (e.g. with blkdebug) on
an IDE device and using rerror/werror=stop to stop the VM. When continuing
the VM, qemu segfaults.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 async.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/async.c b/async.c
index 57ac3a8..fd313df 100644
--- a/async.c
+++ b/async.c
@@ -137,11 +137,12 @@ QEMUBH *qemu_bh_new(QEMUBHFunc *cb, void *opaque)
 
 int qemu_bh_poll(void)
 {
-    QEMUBH *bh, **bhp;
+    QEMUBH *bh, **bhp, *next;
     int ret;
 
     ret = 0;
-    for (bh = async_context->first_bh; bh; bh = bh->next) {
+    for (bh = async_context->first_bh; bh; bh = next) {
+        next = bh->next;
         if (!bh->deleted && bh->scheduled) {
             bh->scheduled = 0;
             if (!bh->idle)
-- 
1.7.5.2

Re: [Qemu-devel] [PATCH] Allow nested qemu_bh_poll() after BH deletion

[Stefan Hajnoczi]

On Wed, Jun 15, 2011 at 11:33 AM, Kevin Wolf <kwolf@redhat.com> wrote:
> Without this, qemu segfaults when a BH handler first deletes its BH and
> then calls another function which involves a nested qemu_bh_poll() call.
>
> This can be reproduced by generating an I/O error (e.g. with blkdebug) on
> an IDE device and using rerror/werror=stop to stop the VM. When continuing
> the VM, qemu segfaults.
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  async.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)

Almost worth switching to qemu-queue.h and FOREACH_SAFE().

Reviewed-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>