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[PULL,1/2] block/iscsi: use a bh to schedule co reentrance

Message ID 1387579525-6224-2-git-send-email-pbonzini@redhat.com
State New
Headers show

Commit Message

Paolo Bonzini Dec. 20, 2013, 10:45 p.m. UTC 
From: Peter Lieven <pl@kamp.de>

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>
---
 block/iscsi.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)
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Patch

diff --git a/block/iscsi.c b/block/iscsi.c
index fa69408..b0e6eea 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -68,6 +68,7 @@  typedef struct IscsiTask {
     int do_retry;
     struct scsi_task *task;
     Coroutine *co;
+    QEMUBH *bh;
 } IscsiTask;
 
 typedef struct IscsiAIOCB {
@@ -123,6 +124,13 @@  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)
@@ -147,7 +155,8 @@  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);
     }
 }