When iocg_kick_delay() is called from a CPU different than the one which set
the delay, @now may be in the past of @iocg->delay_at leading to the
following warning:
UBSAN: shift-out-of-bounds in block/blk-iocost.c:1359:23
shift exponent 18446744073709 is too large for 64-bit type 'u64' (aka 'unsigned long long')
...
Call Trace:
<TASK>
dump_stack_lvl+0x79/0xc0
__ubsan_handle_shift_out_of_bounds+0x2ab/0x300
iocg_kick_delay+0x222/0x230
ioc_rqos_merge+0x1d7/0x2c0
__rq_qos_merge+0x2c/0x80
bio_attempt_back_merge+0x83/0x190
blk_attempt_plug_merge+0x101/0x150
blk_mq_submit_bio+0x2b1/0x720
submit_bio_noacct_nocheck+0x320/0x3e0
__swap_writepage+0x2ab/0x9d0
The underflow itself doesn't really affect the behavior in any meaningful
way; however, the past timestamp may exaggerate the delay amount calculated
later in the code, which shouldn't be a material problem given the nature of
the delay mechanism.
If @now is in the past, this CPU is racing another CPU which recently set up
the delay and there's nothing this CPU can contribute w.r.t. the delay.
Let's bail early from iocg_kick_delay() in such cases.
Reported-by: Breno Leit?o <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>
Fixes: 5160a5a53c0c ("blk-iocost: implement delay adjustment hysteresis")
---
block/blk-iocost.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 089fcb9cfce3..7ee8d85c2c68 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -1353,6 +1353,13 @@ static bool iocg_kick_delay(struct ioc_gq *iocg, struct ioc_now *now)
lockdep_assert_held(&iocg->waitq.lock);
+ /*
+ * If the delay is set by another CPU, we may be in the past. No need to
+ * change anything if so. This avoids decay calculation underflow.
+ */
+ if (time_before64(now->now, iocg->delay_at))
+ return false;
+
/* calculate the current delay in effect - 1/2 every second */
tdelta = now->now - iocg->delay_at;
if (iocg->delay)
On Mon, 20 Nov 2023 12:25:56 -1000, Tejun Heo wrote:
> When iocg_kick_delay() is called from a CPU different than the one which set
> the delay, @now may be in the past of @iocg->delay_at leading to the
> following warning:
>
> UBSAN: shift-out-of-bounds in block/blk-iocost.c:1359:23
> shift exponent 18446744073709 is too large for 64-bit type 'u64' (aka 'unsigned long long')
> ...
> Call Trace:
> <TASK>
> dump_stack_lvl+0x79/0xc0
> __ubsan_handle_shift_out_of_bounds+0x2ab/0x300
> iocg_kick_delay+0x222/0x230
> ioc_rqos_merge+0x1d7/0x2c0
> __rq_qos_merge+0x2c/0x80
> bio_attempt_back_merge+0x83/0x190
> blk_attempt_plug_merge+0x101/0x150
> blk_mq_submit_bio+0x2b1/0x720
> submit_bio_noacct_nocheck+0x320/0x3e0
> __swap_writepage+0x2ab/0x9d0
>
> [...]
Applied, thanks!
[1/1] blk-iocost: Fix an UBSAN shift-out-of-bounds warning
(no commit info)
Best regards,
--
Jens Axboe