Re: [PATCH] thread-pool: Allow at least 1 thread in thread_pool_adjust_max_threads_to_work()

[Fabiano Rosas <farosas@suse.de>]

"Maciej S. Szmigiero" <mail@maciej.szmigiero.name> writes:

> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
>
> thread_pool_adjust_max_threads_to_work() is supposed to give each task its
> own thread by setting the pool max thread count limit accordingly.
>
> However, if there aren't any tasks currently in the pool the pool max
> thread count will be set to 0, which will trigger an assertion failure
> in thread_pool_set_max_threads() - because setting this value would
> completely block the pool by not allowing it to process any submitted
> tasks.
>
> This also can happen if a task is submitted via
> thread_pool_submit_immediate() to an empty pool but the task completes so
> quickly that by the time this function calls
> thread_pool_adjust_max_threads_to_work() the pool again has no unfinished
> tasks in it.
>
> Fix this by making sure that the pool is allowed to create at least 1
> thread.
>
> Fixes: b5aa74968b27 ("thread-pool: Implement generic (non-AIO) pool support")
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> ---
>  util/thread-pool.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/util/thread-pool.c b/util/thread-pool.c
> index 8f8cb38d5ce0..4e75191c983e 100644
> --- a/util/thread-pool.c
> +++ b/util/thread-pool.c
> @@ -493,5 +493,5 @@ bool thread_pool_adjust_max_threads_to_work(ThreadPool *pool)
>  {
>      QEMU_LOCK_GUARD(&pool->cur_work_lock);
>  
> -    return thread_pool_set_max_threads(pool, pool->cur_work);
> +    return thread_pool_set_max_threads(pool, MAX(pool->cur_work, 1));
>  }

Reviewed-by: Fabiano Rosas <farosas@suse.de>