Re: [libvirt PATCH 3/5] qemu,lxc: remove use to nwfilter update lock

[Laine Stump <laine@xxxxxxxxxx>]

On 2/25/22 10:30 AM, Daniel P. Berrangé wrote:
> Now that the virNWFilterBinding APIs are using the nwfilter
> update lock directly, there is no need for the virt drivers
> to do it themselves.

I'm always nervous when the ordering of locks is changed, and that's 
what is happening with the combination of this patch and the previous 
patch. Before it was always the NWFilterLock that was acquired first, 
and then the domain object is retrieved (which involves getting the 
domain-list lock while getting a ref to the domain object).

But since holding of the domain-list lock is localized to that short 
period (and certainly never across a call to the NWFilter binding API) 
I'm fairly certain this (along with the previous patch) is safe from 
creating any new deadlocks.

> Signed-off-by: Daniel P. Berrangé <berrange@xxxxxxxxxx>

Reviewed-by: Laine Stump <laine@xxxxxxxxxx>

> ---
>   src/lxc/lxc_driver.c      |  6 ------
>   src/qemu/qemu_driver.c    | 18 ------------------
>   src/qemu/qemu_migration.c |  3 ---
>   src/qemu/qemu_process.c   |  4 ----
>   4 files changed, 31 deletions(-)
>
> diff --git a/src/lxc/lxc_driver.c b/src/lxc/lxc_driver.c
> index 020ec257ae..4185a61267 100644
> --- a/src/lxc/lxc_driver.c
> +++ b/src/lxc/lxc_driver.c
> @@ -971,8 +971,6 @@ static int lxcDomainCreateWithFiles(virDomainPtr dom,
>   
>       virCheckFlags(VIR_DOMAIN_START_AUTODESTROY, -1);
>   
> -    virNWFilterReadLockFilterUpdates();
> -
>       if (!(vm = lxcDomObjFromDomain(dom)))
>           goto cleanup;
>   
> @@ -1014,7 +1012,6 @@ static int lxcDomainCreateWithFiles(virDomainPtr dom,
>    cleanup:
>       virDomainObjEndAPI(&vm);
>       virObjectEventStateQueue(driver->domainEventState, event);
> -    virNWFilterUnlockFilterUpdates();
>       return ret;
>   }
>   
> @@ -1080,8 +1077,6 @@ lxcDomainCreateXMLWithFiles(virConnectPtr conn,
>       if (flags & VIR_DOMAIN_START_VALIDATE)
>           parse_flags |= VIR_DOMAIN_DEF_PARSE_VALIDATE_SCHEMA;
>   
> -    virNWFilterReadLockFilterUpdates();
> -
>       if (!(caps = virLXCDriverGetCapabilities(driver, false)))
>           goto cleanup;
>   
> @@ -1138,7 +1133,6 @@ lxcDomainCreateXMLWithFiles(virConnectPtr conn,
>    cleanup:
>       virDomainObjEndAPI(&vm);
>       virObjectEventStateQueue(driver->domainEventState, event);
> -    virNWFilterUnlockFilterUpdates();
>       return dom;
>   }
>   
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index b74b0375a7..e4e1cd7bdf 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -1606,8 +1606,6 @@ static virDomainPtr qemuDomainCreateXML(virConnectPtr conn,
>       if (flags & VIR_DOMAIN_START_RESET_NVRAM)
>           start_flags |= VIR_QEMU_PROCESS_START_RESET_NVRAM;
>   
> -    virNWFilterReadLockFilterUpdates();
> -
>       if (!(def = virDomainDefParseString(xml, driver->xmlopt,
>                                           NULL, parse_flags)))
>           goto cleanup;
> @@ -1661,7 +1659,6 @@ static virDomainPtr qemuDomainCreateXML(virConnectPtr conn,
>       virDomainObjEndAPI(&vm);
>       virObjectEventStateQueue(driver->domainEventState, event);
>       virObjectEventStateQueue(driver->domainEventState, event2);
> -    virNWFilterUnlockFilterUpdates();
>       return dom;
>   }
>   
> @@ -5776,8 +5773,6 @@ qemuDomainRestoreFlags(virConnectPtr conn,
>       if (flags & VIR_DOMAIN_SAVE_RESET_NVRAM)
>           reset_nvram = true;
>   
> -    virNWFilterReadLockFilterUpdates();
> -
>       fd = qemuSaveImageOpen(driver, NULL, path, &def, &data,
>                              (flags & VIR_DOMAIN_SAVE_BYPASS_CACHE) != 0,
>                              &wrapperFd, false, false);
> @@ -5849,7 +5844,6 @@ qemuDomainRestoreFlags(virConnectPtr conn,
>       if (vm && ret < 0)
>           qemuDomainRemoveInactiveJob(driver, vm);
>       virDomainObjEndAPI(&vm);
> -    virNWFilterUnlockFilterUpdates();
>       return ret;
>   }
>   
> @@ -6403,8 +6397,6 @@ qemuDomainCreateWithFlags(virDomainPtr dom, unsigned int flags)
>                     VIR_DOMAIN_START_FORCE_BOOT |
>                     VIR_DOMAIN_START_RESET_NVRAM, -1);
>   
> -    virNWFilterReadLockFilterUpdates();
> -
>       if (!(vm = qemuDomainObjFromDomain(dom)))
>           goto cleanup;
>   
> @@ -6433,7 +6425,6 @@ qemuDomainCreateWithFlags(virDomainPtr dom, unsigned int flags)
>   
>    cleanup:
>       virDomainObjEndAPI(&vm);
> -    virNWFilterUnlockFilterUpdates();
>       return ret;
>   }
>   
> @@ -7815,8 +7806,6 @@ qemuDomainAttachDeviceFlags(virDomainPtr dom,
>       virDomainObj *vm = NULL;
>       int ret = -1;
>   
> -    virNWFilterReadLockFilterUpdates();
> -
>       if (!(vm = qemuDomainObjFromDomain(dom)))
>           goto cleanup;
>   
> @@ -7839,7 +7828,6 @@ qemuDomainAttachDeviceFlags(virDomainPtr dom,
>   
>    cleanup:
>       virDomainObjEndAPI(&vm);
> -    virNWFilterUnlockFilterUpdates();
>       return ret;
>   }
>   
> @@ -7869,8 +7857,6 @@ static int qemuDomainUpdateDeviceFlags(virDomainPtr dom,
>                     VIR_DOMAIN_AFFECT_CONFIG |
>                     VIR_DOMAIN_DEVICE_MODIFY_FORCE, -1);
>   
> -    virNWFilterReadLockFilterUpdates();
> -
>       cfg = virQEMUDriverGetConfig(driver);
>   
>       if (!(vm = qemuDomainObjFromDomain(dom)))
> @@ -7947,7 +7933,6 @@ static int qemuDomainUpdateDeviceFlags(virDomainPtr dom,
>       if (dev != dev_copy)
>           virDomainDeviceDefFree(dev_copy);
>       virDomainObjEndAPI(&vm);
> -    virNWFilterUnlockFilterUpdates();
>       return ret;
>   }
>   
> @@ -13654,8 +13639,6 @@ qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
>       virDomainObj *vm = NULL;
>       int ret = -1;
>   
> -    virNWFilterReadLockFilterUpdates();
> -
>       if (!(vm = qemuDomObjFromSnapshot(snapshot)))
>           goto cleanup;
>   
> @@ -13666,7 +13649,6 @@ qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
>   
>    cleanup:
>       virDomainObjEndAPI(&vm);
> -    virNWFilterUnlockFilterUpdates();
>       return ret;
>   }
>   
> diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
> index 5aecdddff0..43ee094486 100644
> --- a/src/qemu/qemu_migration.c
> +++ b/src/qemu/qemu_migration.c
> @@ -2782,8 +2782,6 @@ qemuMigrationDstPrepareAny(virQEMUDriver *driver,
>       int rv;
>       g_autofree char *tlsAlias = NULL;
>   
> -    virNWFilterReadLockFilterUpdates();
> -
>       if (flags & VIR_MIGRATE_OFFLINE) {
>           if (flags & (VIR_MIGRATE_NON_SHARED_DISK |
>                        VIR_MIGRATE_NON_SHARED_INC)) {
> @@ -3103,7 +3101,6 @@ qemuMigrationDstPrepareAny(virQEMUDriver *driver,
>       virDomainObjEndAPI(&vm);
>       virObjectEventStateQueue(driver->domainEventState, event);
>       qemuMigrationCookieFree(mig);
> -    virNWFilterUnlockFilterUpdates();
>       virErrorRestore(&origErr);
>       return ret;
>   
> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
> index 5af925e521..b19a6218d0 100644
> --- a/src/qemu/qemu_process.c
> +++ b/src/qemu/qemu_process.c
> @@ -9004,7 +9004,6 @@ qemuProcessReconnect(void *opaque)
>               qemuDomainRemoveInactiveJob(driver, obj);
>       }
>       virDomainObjEndAPI(&obj);
> -    virNWFilterUnlockFilterUpdates();
>       virIdentitySetCurrent(NULL);
>       return;
>   
> @@ -9056,8 +9055,6 @@ qemuProcessReconnectHelper(virDomainObj *obj,
>       data->obj = obj;
>       data->identity = virIdentityGetCurrent();
>   
> -    virNWFilterReadLockFilterUpdates();
> -
>       /* this lock and reference will be eventually transferred to the thread
>        * that handles the reconnect */
>       virObjectLock(obj);
> @@ -9080,7 +9077,6 @@ qemuProcessReconnectHelper(virDomainObj *obj,
>           qemuDomainRemoveInactiveJobLocked(src->driver, obj);
>   
>           virDomainObjEndAPI(&obj);
> -        virNWFilterUnlockFilterUpdates();
>           g_clear_object(&data->identity);
>           VIR_FREE(data);
>           return -1;