Re: [PATCH v4 02/11] liveupdate: Synchronize lazy initialization of FLB private state

[Mike Rapoport]

On Mon, Apr 13, 2026 at 06:51:18PM +0000, Pasha Tatashin wrote:
> The luo_flb_get_private() function, which is responsible for lazily
> initializing the private state of FLB objects, can be called
> concurrently from multiple threads. This creates a data
> race on the 'initialized' flag and can lead to multiple executions of
> mutex_init() and INIT_LIST_HEAD() on the same memory.
> 
> Introduce a static spinlock (luo_flb_init_lock) local to the function
> to synchronize the initialization path. Use smp_load_acquire() and
> smp_store_release() for memory ordering between the fast path and the
> slow path.
> 
> Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
> Reviewed-by: Pratyush Yadav (Google) <pratyush@xxxxxxxxxx>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>

> ---
>  kernel/liveupdate/luo_flb.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/liveupdate/luo_flb.c b/kernel/liveupdate/luo_flb.c
> index f52e8114837e..cf4a8f854c83 100644
> --- a/kernel/liveupdate/luo_flb.c
> +++ b/kernel/liveupdate/luo_flb.c
> @@ -89,13 +89,18 @@ struct luo_flb_link {
>  static struct luo_flb_private *luo_flb_get_private(struct liveupdate_flb *flb)
>  {
>  	struct luo_flb_private *private = &ACCESS_PRIVATE(flb, private);
> +	static DEFINE_SPINLOCK(luo_flb_init_lock);
>  
> +	if (smp_load_acquire(&private->initialized))
> +		return private;
> +
> +	guard(spinlock)(&luo_flb_init_lock);
>  	if (!private->initialized) {
>  		mutex_init(&private->incoming.lock);
>  		mutex_init(&private->outgoing.lock);
>  		INIT_LIST_HEAD(&private->list);
>  		private->users = 0;
> -		private->initialized = true;
> +		smp_store_release(&private->initialized, true);
>  	}
>  
>  	return private;
> -- 
> 2.43.0
> 

-- 
Sincerely yours,
Mike.