Messages in this thread | | | Subject | Re: [PATCH BUGFIX] block, bfq: fix delayed stable merge check | From | Holger Hoffstätte <> | Date | Mon, 24 May 2021 20:45:37 +0200 |
| |
On 2021-05-24 19:41, Paolo Valente wrote: > > >> Il giorno 24 mag 2021, alle ore 19:13, Holger Hoffstätte <holger@applied-asynchrony.com> ha scritto: >> >> On 2021-05-24 18:57, Paolo Valente wrote: >>>> Il giorno 20 mag 2021, alle ore 09:15, Holger Hoffstätte <holger@applied-asynchrony.com> ha scritto: >>>> >>>> On 2021-05-18 12:43, Luca Mariotti wrote: >>>>> When attempting to schedule a merge of a given bfq_queue with the currently >>>>> in-service bfq_queue or with a cooperating bfq_queue among the scheduled >>>>> bfq_queues, delayed stable merge is checked for rotational or non-queueing >>>>> devs. For this stable merge to be performed, some conditions must be met. >>>>> If the current bfq_queue underwent some split from some merged bfq_queue, >>>>> one of these conditions is that two hundred milliseconds must elapse from >>>>> split, otherwise this condition is always met. >>>>> Unfortunately, by mistake, time_is_after_jiffies() was written instead of >>>>> time_is_before_jiffies() for this check, verifying that less than two >>>>> hundred milliseconds have elapsed instead of verifying that at least two >>>>> hundred milliseconds have elapsed. >>>>> Fix this issue by replacing time_is_after_jiffies() with >>>>> time_is_before_jiffies(). >>>>> Signed-off-by: Luca Mariotti <mariottiluca1@hotmail.it> >>>>> Signed-off-by: Paolo Valente <paolo.valente@linaro.org> >>>>> Signed-off-by: Pietro Pedroni <pedroni.pietro.96@gmail.com> >>>>> --- >>>>> block/bfq-iosched.c | 2 +- >>>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>>> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c >>>>> index acd1f881273e..2adb1e69c9d2 100644 >>>>> --- a/block/bfq-iosched.c >>>>> +++ b/block/bfq-iosched.c >>>>> @@ -2697,7 +2697,7 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq, >>>>> if (unlikely(!bfqd->nonrot_with_queueing)) { >>>>> if (bic->stable_merge_bfqq && >>>>> !bfq_bfqq_just_created(bfqq) && >>>>> - time_is_after_jiffies(bfqq->split_time + >>>>> + time_is_before_jiffies(bfqq->split_time + >>>>> msecs_to_jiffies(200))) { >>>>> struct bfq_queue *stable_merge_bfqq = >>>>> bic->stable_merge_bfqq; >>>> >>>> Not sure why but with this patch I quickly got a division-by-zero in BFQ and >>>> complete system halt. Unfortunately I couldn't capture the exact stack trace, >>>> but it read something like bfq_calc_weight() or something ike that. >>>> I looked through the code and found bfq_delta(), so maybe weight got >>>> reduced to 0? >>>> >>> Hi Holger, >>> is this (easily) reproducible for you? If so, I'd like to propose you >>> a candidate fix. >> >> Yes, it's easily reproducible (should be reproducible on 5.13-rc as well). >> Simple read/write I/O on a cold FS (rotational disk obviously) will crash >> pretty much immediately; without it everything works fine, likely because the >> bug (in the recent queue merging patches?) is never triggered due to the >> accidentally-wrong time calculation. > > Exactly! > > Unfortunately, no crash happens on my systems. Or, actually, crashes > stopped after the attached fix. > >> Will gladly test your patch! :) >> > > Here it is! > > I'll make a proper commit after your early tests. > > Crossing my fingers, > Paolo
That did it - it now survived a bunch of heavy read/write/mixed I/O that would previously crash right away. Maybe it's because btrfs uses several workers and so different IOs got mixed together? Anyway:
Fixes: 430a67f9d616 ("block, bfq: merge bursts of newly-created queues") Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Thanks! Holger
| |