Re: [PATCH] fs: annotate data race in get_nr_inodes()

[Jan Kara]

On Tue 27-10-26 16:08:49, Mani Tofigh via B4 Relay wrote:
> From: Mani Tofigh <mt4022@xxxxxxxxxxxx>
> 
> get_nr_inodes() sums the per-CPU inode counts without a lock, and the
> result is only an estimate, so it's harmless if one of them changes
> during the sum.  Wrap the reads in data_race() to mark this.
> 
>   [   11.857490] BUG: KCSAN: data-race in get_nr_inodes+0x9f/0xf0
> 
>   [   11.857568] race at unknown origin, with read to 0xff1100002b6281e8 of 8 bytes by task 106 on cpu 1:
>   [   11.857621]  get_nr_inodes+0x9f/0xf0
>   [   11.857675]  get_nr_dirty_inodes+0x1d/0x110
>   [   11.857748]  writeback_inodes_sb+0x3d/0x60
>   ...
> 
>   [   11.870052] value changed: 0x00000000000000b3 -> 0x00000000000000b5
> 
> Found with KCSAN while fuzzing under a deterministic hypervisor that's
> currently under development.
> 
> Signed-off-by: Mani Tofigh <mt4022@xxxxxxxxxxxx>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
>  fs/inode.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 1cb6293b237a..ee4366264c36 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -79,7 +79,7 @@ static long get_nr_inodes(void)
>  	int i;
>  	long sum = 0;
>  	for_each_possible_cpu(i)
> -		sum += per_cpu(nr_inodes, i);
> +		sum += data_race(per_cpu(nr_inodes, i));
>  	return sum < 0 ? 0 : sum;
>  }
>  
> 
> ---
> base-commit: d135ab453a7400a34930bdda1ef4bdc8acfac80e
> change-id: 20261027-kcsan-inode-ad562064d53f
> 
> Best regards,
> --  
> Mani Tofigh <mt4022@xxxxxxxxxxxx>
> 
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR