[Qemu-devel] [PATCH] AHCI: Fix port reset race

[Alexander Graf]

bdrv_aio_cancel() can trigger bdrv_aio_flush() which makes all aio
that is currently in flight finish. So what we do is:

  port reset
  detect ncq in flight
  cancel ncq
  delete ncq sg list

at which point we have double freed the sg list. Instead, with this
patch we do:

  port reset
  detect ncq in flight
  cancel ncq
  check if we are really still in flight
  delete ncq sg list

which makes things work and gets rid of the race.

Signed-off-by: Alexander Graf <address@hidden>
---
 hw/ide/ahci.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
index 8869fd6..c2c168d 100644
--- a/hw/ide/ahci.c
+++ b/hw/ide/ahci.c
@@ -560,6 +560,11 @@ static void ahci_reset_port(AHCIState *s, int port)
             ncq_tfs->aiocb = NULL;
         }
 
+        /* Maybe we just finished the request thanks to bdrv_aio_cancel() */
+        if (!ncq_tfs->used) {
+            continue;
+        }
+
         qemu_sglist_destroy(&ncq_tfs->sglist);
         ncq_tfs->used = 0;
     }
-- 
1.6.0.2