5.15-stable review patch. If anyone has any objections, please let me know.
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From: Tejun Heo tj@kernel.org
[ Upstream commit 2a427b49d02995ea4a6ff93a1432c40fa4d36821 ]
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 Leitão leitao@debian.org Signed-off-by: Tejun Heo tj@kernel.org Fixes: 5160a5a53c0c ("blk-iocost: implement delay adjustment hysteresis") Link: https://lore.kernel.org/r/ZVvc9L_CYk5LO1fT@slm.duckdns.org Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/blk-iocost.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/block/blk-iocost.c b/block/blk-iocost.c index f95feabb3ca8..645a589edda8 100644 --- a/block/blk-iocost.c +++ b/block/blk-iocost.c @@ -1342,6 +1342,13 @@ 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)