[Qemu-devel] [PATCH 4/5] migration: add missed aio_context_acquire into hmp_savevm/hmp_delvm

[Denis V. Lunev]

aio_context should be locked in the similar way as was done in QMP
snapshot creation in the other case there are a lot of possible
troubles if native AIO mode is enabled for disk.

- the command can hang (HMP thread) with missed wakeup (the operation is
  actually complete)
    io_submit
    ioq_submit
    laio_submit
    raw_aio_submit
    raw_aio_readv
    bdrv_co_io_em
    bdrv_co_readv_em
    bdrv_aligned_preadv
    bdrv_co_do_preadv
    bdrv_co_do_readv
    bdrv_co_readv
    qcow2_co_readv
    bdrv_aligned_preadv
    bdrv_co_do_pwritev
    bdrv_rw_co_entry

- QEMU can assert in coroutine re-enter
    __GI_abort
    qemu_coroutine_enter
    bdrv_co_io_em_complete
    qemu_laio_process_completion
    qemu_laio_completion_bh
    aio_bh_poll
    aio_dispatch
    aio_poll
    iothread_run

AioContext lock is reqursive. Thus nested locking should not be a problem.

Signed-off-by: Denis V. Lunev <d...@openvz.org>
CC: Stefan Hajnoczi <stefa...@redhat.com>
CC: Paolo Bonzini <pbonz...@redhat.com>
CC: Juan Quintela <quint...@redhat.com>
CC: Amit Shah <amit.s...@redhat.com>
---
 block/snapshot.c   | 5 +++++
 migration/savevm.c | 7 +++++++
 2 files changed, 12 insertions(+)

diff --git a/block/snapshot.c b/block/snapshot.c
index 89500f2..f6fa17a 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -259,6 +259,9 @@ void bdrv_snapshot_delete_by_id_or_name(BlockDriverState 
*bs,
 {
     int ret;
     Error *local_err = NULL;
+    AioContext *aio_context = bdrv_get_aio_context(bs);
+
+    aio_context_acquire(aio_context);
 
     ret = bdrv_snapshot_delete(bs, id_or_name, NULL, &local_err);
     if (ret == -ENOENT || ret == -EINVAL) {
@@ -267,6 +270,8 @@ void bdrv_snapshot_delete_by_id_or_name(BlockDriverState 
*bs,
         ret = bdrv_snapshot_delete(bs, NULL, id_or_name, &local_err);
     }
 
+    aio_context_release(aio_context);
+
     if (ret < 0) {
         error_propagate(errp, local_err);
     }
diff --git a/migration/savevm.c b/migration/savevm.c
index dbcc39a..83d2efa 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1289,6 +1289,7 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
     struct tm tm;
     const char *name = qdict_get_try_str(qdict, "name");
     Error *local_err = NULL;
+    AioContext *aio_context;
 
     /* Verify if there is a device that doesn't support snapshots and is 
writable */
     bs = NULL;
@@ -1320,6 +1321,9 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
     }
     vm_stop(RUN_STATE_SAVE_VM);
 
+    aio_context = bdrv_get_aio_context(bs);
+    aio_context_acquire(aio_context);
+
     memset(sn, 0, sizeof(*sn));
 
     /* fill auxiliary fields */
@@ -1378,6 +1382,8 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
     }
 
  the_end:
+    aio_context_release(aio_context);
+
     if (saved_vm_running) {
         vm_start();
     }