[libvirt] [PATCH] virThreadPoolFree: Set n(Prio)Workers after the pool is locked

[Daniel P. Berrange]

On Thu, Dec 05, 2013 at 02:54:41PM +0100, Michal Privoznik wrote:
> In 78839da I am trying to join the worker threads. However, I can't
> sipmly reuse pool->nWorkers (same applies for pool->nPrioWorkers),
> because of the following flow that is currently implemented:
> 
> 1) the main thread executing virThreadPoolFree sets pool->quit = true,
> wakes up all the workers and wait on pool->quit_cond.
> 
> 2) A worker is woken up and see quit request. It immediately jumps of
> the while() loop and decrements pool->nWorkers (or pool->nPrioWorkers in
> case of priority worker). The last thread signalizes pool->quit_cond.
> 
> 3) Main thread is woken up, with both pool->nWorkers and
> pool->nPrioWorkers being zero.
> 
> So there's a need to copy the original value of worker thread counts
> into local variables. However, these need to set *after* the check for
> pool being NULL (dereferencing a NULL is no no). And for safety they can
> be set right after the pool is locked.
> 
> Reported-by: John Ferlan <jferlan at redhat.com>
> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> ---
>  src/util/virthreadpool.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/src/util/virthreadpool.c b/src/util/virthreadpool.c
> index 99f36ec..aa442d1 100644
> --- a/src/util/virthreadpool.c
> +++ b/src/util/virthreadpool.c
> @@ -242,13 +242,15 @@ void virThreadPoolFree(virThreadPoolPtr pool)
>      virThreadPoolJobPtr job;
>      bool priority = false;
>      size_t i;
> -    size_t nWorkers = pool->nWorkers;
> -    size_t nPrioWorkers = pool->nPrioWorkers;
> +    size_t nWorkers;
> +    size_t nPrioWorkers;
>  
>      if (!pool)
>          return;
>  
>      virMutexLock(&pool->mutex);
> +    nWorkers = pool->nWorkers;
> +    nPrioWorkers = pool->nPrioWorkers;
>      pool->quit = true;
>      if (pool->nWorkers > 0)
>          virCondBroadcast(&pool->cond);

ACK

Daniel
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