Re: [PATCH] s390/time: Use jiffies instead of jiffies_64

Heiko Carstens <[email protected]> writes:

> Christoph Schlameuss and Alexander Egorenkov reported a data-race
> reported by KCSAN when jiffies_64 is read:
>
> ==================================================================
> BUG: KCSAN: data-race in do_account_vtime / tick_do_update_jiffies64
>
> write to 0x0000016599ea8600 of 8 bytes by interrupt on cpu 6:
>  tick_do_update_jiffies64+0x140/0x250
> =============================================================>
> BUG: KCSAN: data-race in do_account_vtime / tick_do_update_ji>
>
> write to 0x0000016599ea8600 of 8 bytes by interrupt on cpu 6:
>  tick_do_update_jiffies64+0x140/0x250
>  tick_nohz_handler+0x2e6/0x300
>  __run_hrtimer+0x156/0x4d0
>  __hrtimer_run_queues+0xd2/0x150
> ...
>  system_call+0x72/0x90
>
> read to 0x0000016599ea8600 of 8 bytes by interrupt on cpu 12:
>  do_account_vtime+0x7d6/0x860
>  vtime_flush+0x26/0xe0
>  update_process_times+0x32/0x160
>  tick_nohz_handler+0x12a/0x300
> ...
>  system_call+0x72/0x90
>
> value changed: 0x00000000ffffaa6c -> 0x00000000ffffaa6d
> ...
> =============================================================>
>
> Problem is that jiffies_64 instead of jiffies is used. Both are at the
> same address, but only jiffies is of volatile type, which prevents this
> warning.
>
> Change the vtime code so jiffies instead of jiffies_64 is used
> everywhere. This addresses also the inconsistency that both jiffies and
> jiffies_64 were used in the original patch which introduced this.
>
> Fixes: f341b8dff982 ("s390/vtime: limit MT scaling value updates")
> Reported-by: Christoph Schlameuss <[email protected]>
> Reported-by: Alexander Egorenkov <[email protected]>
> Signed-off-by: Heiko Carstens <[email protected]>

Reviewed-by: Alexander Egorenkov <[email protected]>
Tested-by: Alexander Egorenkov <[email protected]>