[Qemu-devel] [PATCH] rbd block driver fix race between aio completition and aio cancel

[Stefan Priebe]

From: Stefan Priebe <address@hidden>

This one fixes a race qemu also had in iscsi block driver between
cancellation and io completition.

qemu_rbd_aio_cancel was not synchronously waiting for the end of
the command.

It also removes the useless cancelled flag and introduces instead
a status flag with EINPROGRESS like iscsi block driver.

Signed-off-by: Stefan Priebe <address@hidden>
---
 block/rbd.c |   19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/block/rbd.c b/block/rbd.c
index 5a0f79f..7b3bcbb 100644
--- a/block/rbd.c
+++ b/block/rbd.c
@@ -76,7 +76,7 @@ typedef struct RBDAIOCB {
     int64_t sector_num;
     int error;
     struct BDRVRBDState *s;
-    int cancelled;
+    int status;
 } RBDAIOCB;
 
 typedef struct RADOSCB {
@@ -376,9 +376,7 @@ static void qemu_rbd_complete_aio(RADOSCB *rcb)
     RBDAIOCB *acb = rcb->acb;
     int64_t r;
 
-    if (acb->cancelled) {
-        qemu_vfree(acb->bounce);
-        qemu_aio_release(acb);
+    if (acb->bh) {
         goto done;
     }
 
@@ -406,9 +404,12 @@ static void qemu_rbd_complete_aio(RADOSCB *rcb)
             acb->ret = r;
         }
     }
+    acb->status = acb->ret;
+
     /* Note that acb->bh can be NULL in case where the aio was cancelled */
     acb->bh = qemu_bh_new(rbd_aio_bh_cb, acb);
     qemu_bh_schedule(acb->bh);
+
 done:
     g_free(rcb);
 }
@@ -573,7 +574,10 @@ static void qemu_rbd_close(BlockDriverState *bs)
 static void qemu_rbd_aio_cancel(BlockDriverAIOCB *blockacb)
 {
     RBDAIOCB *acb = (RBDAIOCB *) blockacb;
-    acb->cancelled = 1;
+
+    while (acb->status == -EINPROGRESS) {
+        qemu_aio_wait();
+    }
 }
 
 static AIOPool rbd_aio_pool = {
@@ -642,10 +646,11 @@ static void rbd_aio_bh_cb(void *opaque)
         qemu_iovec_from_buf(acb->qiov, 0, acb->bounce, acb->qiov->size);
     }
     qemu_vfree(acb->bounce);
-    acb->common.cb(acb->common.opaque, (acb->ret > 0 ? 0 : acb->ret));
     qemu_bh_delete(acb->bh);
     acb->bh = NULL;
 
+    acb->common.cb(acb->common.opaque, (acb->ret > 0 ? 0 : acb->ret));
+
     qemu_aio_release(acb);
 }
 
@@ -689,8 +694,8 @@ static BlockDriverAIOCB *rbd_start_aio(BlockDriverState *bs,
     acb->ret = 0;
     acb->error = 0;
     acb->s = s;
-    acb->cancelled = 0;
     acb->bh = NULL;
+    acb->status = -EINPROGRESS;
 
     if (cmd == RBD_AIO_WRITE) {
         qemu_iovec_to_buf(acb->qiov, 0, acb->bounce, qiov->size);
-- 
1.7.10.4