From: Tejun Heo tj@kernel.org
commit 8c936f9ea11ec4e35e288810a7503b5c841a355f upstream.
When an iocg is in debt, its inuse weight is owned by debt handling and should stay at 1. This invariant was broken when determining the amount of surpluses at the beginning of donation calculation - when an iocg's hierarchical weight is too low, the iocg is excluded from donation calculation and its inuse is reset to its active regardless of its indebtedness, triggering warnings like the following:
WARNING: CPU: 5 PID: 0 at block/blk-iocost.c:1416 iocg_kick_waitq+0x392/0x3a0 ... RIP: 0010:iocg_kick_waitq+0x392/0x3a0 Code: 00 00 be ff ff ff ff 48 89 4d a8 e8 98 b2 70 00 48 8b 4d a8 85 c0 0f 85 4a fe ff ff 0f 0b e9 43 fe ff ff 0f 0b e9 4d fe ff ff <0f> 0b e9 50 fe ff ff e8 a2 ae 70 00 66 90 0f 1f 44 00 00 55 48 89 RSP: 0018:ffffc90000200d08 EFLAGS: 00010016 ... <IRQ> ioc_timer_fn+0x2e0/0x1470 call_timer_fn+0xa1/0x2c0 ...
As this happens only when an iocg's hierarchical weight is negligible, its impact likely is limited to triggering the warnings. Fix it by skipping resetting inuse of under-weighted debtors.
Signed-off-by: Tejun Heo tj@kernel.org Reported-by: Rik van Riel riel@surriel.com Fixes: c421a3eb2e27 ("blk-iocost: revamp debt handling") Cc: stable@vger.kernel.org # v5.10+ Link: https://lore.kernel.org/r/YmjODd4aif9BzFuO@slm.duckdns.org Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- block/blk-iocost.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)
--- a/block/blk-iocost.c +++ b/block/blk-iocost.c @@ -2257,7 +2257,17 @@ static void ioc_timer_fn(struct timer_li iocg->hweight_donating = hwa; iocg->hweight_after_donation = new_hwi; list_add(&iocg->surplus_list, &surpluses); - } else { + } else if (!iocg->abs_vdebt) { + /* + * @iocg doesn't have enough to donate. Reset + * its inuse to active. + * + * Don't reset debtors as their inuse's are + * owned by debt handling. This shouldn't affect + * donation calculuation in any meaningful way + * as @iocg doesn't have a meaningful amount of + * share anyway. + */ TRACE_IOCG_PATH(inuse_shortage, iocg, &now, iocg->inuse, iocg->active, iocg->hweight_inuse, new_hwi);