Re: [PATCH v2] buffer: Annotate the remote buffer LRU occupancy check

[Jan Kara]

On Thu 12-11-26 09:50:47, Zhu Jun wrote:
> has_bh_in_lru() reads another CPU's buffer LRU while that CPU may install
> or invalidate entries. The local BH LRU lock does not serialize this
> remote occupancy check, which KCSAN reports as a data race.
> 
> The check only decides whether to send a drain IPI and never dereferences
> the sampled pointer. Mark the occupancy check as an intentional data
> race with data_race().
> 
> Fixes: 42be35d0390b ("fs: only send IPI to invalidate LRU BH when needed")
> Signed-off-by: Zhu Jun <zhujun2@xxxxxxxxxxxxxxxxxxxx>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
> Changes in v2:
> - Use data_race() without READ_ONCE().
> - Drop the added comment, as suggested by Jan Kara.
> 
>  fs/buffer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 5d3852b726d6..2d2d61495b4d 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1437,7 +1437,7 @@ bool has_bh_in_lru(int cpu, void *dummy)
>  	int i;
>  	
>  	for (i = 0; i < BH_LRU_SIZE; i++) {
> -		if (b->bhs[i])
> +		if (data_race(b->bhs[i]))
>  			return true;
>  	}
>  
> -- 
> 2.51.0
> 
> 
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR