[libvirt] [PATCH] util: make use of VIR_LOCK_SPACE_ACQUIRE_AUTOCREATE in virLockSpaceAcquireResource

[Daniel P. Berrange]

On Thu, Feb 12, 2015 at 07:12:57PM +0800, Shanzhi Yu wrote:
> When create external disk snapshot with virtlock enabled, libvirtd
> will hang if flag VIR_LOCK_SPACE_ACQUIRE_AUTOCREATE is missed in
> virLockSpaceAcquireResource.
> 
> Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1191901
> Signed-off-by: Shanzhi Yu <shyu at redhat.com>
> ---
>  src/util/virlockspace.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/src/util/virlockspace.c b/src/util/virlockspace.c
> index 2366a74..25b4433 100644
> --- a/src/util/virlockspace.c
> +++ b/src/util/virlockspace.c
> @@ -626,8 +626,10 @@ int virLockSpaceAcquireResource(virLockSpacePtr lockspace,
>      virMutexLock(&lockspace->lock);
>  
>      if ((res = virHashLookup(lockspace->resources, resname))) {
> -        if ((res->flags & VIR_LOCK_SPACE_ACQUIRE_SHARED) &&
> -            (flags & VIR_LOCK_SPACE_ACQUIRE_SHARED)) {
> +        if (((res->flags & VIR_LOCK_SPACE_ACQUIRE_SHARED) &&
> +            (flags & VIR_LOCK_SPACE_ACQUIRE_SHARED)) ||
> +            ((res->flags & VIR_LOCK_SPACE_ACQUIRE_AUTOCREATE) &&
> +            (flags & VIR_LOCK_SPACE_ACQUIRE_AUTOCREATE))){

No, this is wrong. If virHashLookup returns a non-NULL entry it
indicates that the lock is already held. It is not valid to
ignore this error if 'autocreate' flag is set, as that would allow
multiple VMs to own the same disk which is exactly the scenario we
are trying to prevent.

Regards,
Daniel
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