Re: [libvirt] storage lock issues
On 11/02/2017 11:44 AM, Cedric Bosdonnat wrote:
On Thu, 2017-11-02 at 07:03 -0400, John Ferlan wrote:
> So how to fix - well seems to me the storageDriverLock in VolCreateXML
> may be the way since the refresh thread takes the driver lock first,
> then the pool object second. Perhaps even like the build code where it
> takes it temporarily while getting the pool object. I'd have to think a
> bit more about though. Still might be something to try since the Vol
> Refresh thread takes it while running...
This is surely a bad hack, but this is fixing the problem I'm seeing.
Wouldn't the VolCreateXML function taking the lock for a too long time
and thus lead to other troubles?
This was my first gut reaction (that is the fix you chose), but I wanted
to take the time to make sure paths being called wouldn't have deadlocks
as well and of course to check history to ensure someone didn't remove
the lock for a specific reason.
You are correct it's a long time to hold that storageDriverLock, but the
alternative is the crash you found. We hold that lock many other long
running storage pool operations.
BTW: A different solution could to follow how storageVolCreateXMLFrom
does things. It only uses the lock around storage pool obj operations.
While I'm thinking about it - Vol Delete perhaps should do some locking too.
Again once the Storage/Vol code gets the common object and uses RW Locks
- many of the existing DriverLock/Unlock won't be necessary because the
storage pool and storage volume lists would be self locking.
---- %< ----
diff --git a/src/storage/storage_driver.c b/src/storage/storage_driver.c
index 18d630319..f5a1e7bc2 100644
--- a/src/storage/storage_driver.c
+++ b/src/storage/storage_driver.c
@@ -1825,6 +1825,7 @@ storageVolCreateXML(virStoragePoolPtr obj,
if (backend->createVol(obj->conn, pool, voldef) < 0)
goto cleanup;
+ storageDriverLock();
pool->volumes.objs[pool->volumes.count++] = voldef;
volobj = virGetStorageVol(obj->conn, pool->def->name, voldef->name,
voldef->key, NULL, NULL);
@@ -1858,9 +1859,7 @@ storageVolCreateXML(virStoragePoolPtr obj,
VIR_FREE(buildvoldef);
- storageDriverLock();
virStoragePoolObjLock(pool);
- storageDriverUnlock();
voldef->building = false;
pool->asyncjobs--;
@@ -1897,6 +1896,7 @@ storageVolCreateXML(virStoragePoolPtr obj,
voldef = NULL;
cleanup:
+ storageDriverUnlock();
If we took it before the PoolObj lock, then we'd need to Unlock after we
unlock the pool obj...
John
virObjectUnref(volobj);
virStorageVolDefFree(voldef);
if (pool)
---- %< ----
--
Cedric