> Il giorno 24 mag 2021, alle ore 19:13, Holger Hoffstätte ha scritto: > > On 2021-05-24 18:57, Paolo Valente wrote: >>> Il giorno 20 mag 2021, alle ore 09:15, Holger Hoffstätte 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 >>>> Signed-off-by: Paolo Valente >>>> Signed-off-by: Pietro Pedroni >>>> --- >>>> 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