Messages in this thread | | | Subject | Re: [RFC PATCH] bfq: fix waker_bfqq inconsistency crash | From | Yu Kuai <> | Date | Thu, 3 Nov 2022 11:51:15 +0800 |
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Hi,
在 2022/11/03 11:05, Khazhy Kumykov 写道: > On Wed, Nov 2, 2022 at 7:56 PM Yu Kuai <yukuai1@huaweicloud.com> wrote: >> >> Hi, >> >> 在 2022/11/03 9:39, Khazhismel Kumykov 写道: >>> This fixes crashes in bfq_add_bfqq_busy due to waker_bfqq being NULL, >>> but woken_list_node still being hashed. This would happen when >>> bfq_init_rq() expects a brand new allocated queue to be returned from >> >> From what I see, bfqq->waker_bfqq is updated in bfq_init_rq() only if >> 'new_queue' is false, but if 'new_queue' is false, the returned 'bfqq' >> from bfq_get_bfqq_handle_split() will never be oom_bfqq, so I'm confused >> here... > There's two calls for bfq_get_bfqq_handle_split in this function - the > second one is after the check you mentioned, and is the problematic > one. Yes, thanks for the explanation. Now I understand how the problem triggers.
>> >>> bfq_get_bfqq_handle_split() and unconditionally updates waker_bfqq >>> without resetting woken_list_node. Since we can always return oom_bfqq >>> when attempting to allocate, we cannot assume waker_bfqq starts as NULL. >>> We must either reset woken_list_node, or avoid setting woken_list at all >>> for oom_bfqq - opt to do the former. >> >> Once oom_bfqq is used, I think the io is treated as issued from root >> group. Hence I don't think it's necessary to set woken_list or >> waker_bfqq for oom_bfqq. > Ack, I was wondering what's right here since, evidently, *someone* had > already set oom_bfqq->waker_bfqq to *something* (although... maybe it > was an earlier init_rq). But maybe it's better to do nothing if we > *know* it's oom_bfqq.
I need to have a check how oom_bfqq get involved with waker_bfqq, and then see if it's reasonable.
Probably Jan and Paolo will have better view on this.
Thanks, Kuai > > Is it a correct interpretation here that setting waker_bfqq won't > accomplish anything anyways on oom_bfqq, so better off not?
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