block/iscsi: use a bh to schedule co reentrance

this fixes a potential segfault and performance regression.

If the coroutine is reentered directly in the iscsi_co_generic_cb
iscsi_process_{read,write} are interrupted and reentered any
time later. One the one hand this could happen after an iscsi_close
where the iscsi context is already gone (segfault). On the
other hand this limits the number of processed callbacks
in each aio_dispatch to one (potential performance regression).

Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 8b9dfe9098d91e06a3dd6376624307fe5fa13be8)

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

diff --git a/block/iscsi.c b/block/iscsi.c
index a2d578c0a7b2b3d56524ed326cdd2fffbfe2713b..a410a28e38fb24342c297cda62771bd113d57075 100644 (file)
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -65,6 +65,7 @@ typedef struct IscsiTask {
     int do_retry;
     struct scsi_task *task;
     Coroutine *co;
+    QEMUBH *bh;
 } IscsiTask;
 
 typedef struct IscsiAIOCB {
@@ -121,6 +122,13 @@ iscsi_schedule_bh(IscsiAIOCB *acb)
     qemu_bh_schedule(acb->bh);
 }
 
+static void iscsi_co_generic_bh_cb(void *opaque)
+{
+    struct IscsiTask *iTask = opaque;
+    qemu_bh_delete(iTask->bh);
+    qemu_coroutine_enter(iTask->co, NULL);
+}
+
 static void
 iscsi_co_generic_cb(struct iscsi_context *iscsi, int status,
                         void *command_data, void *opaque)
@@ -145,7 +153,8 @@ iscsi_co_generic_cb(struct iscsi_context *iscsi, int status,
 
 out:
     if (iTask->co) {
-        qemu_coroutine_enter(iTask->co, NULL);
+        iTask->bh = qemu_bh_new(iscsi_co_generic_bh_cb, iTask);
+        qemu_bh_schedule(iTask->bh);
     }
 }