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From: Satya Durga Srinivasu Prabhala <quic_satyap@quicinc.com>
To: 'Alexei Starovoitov' <alexei.starovoitov@gmail.com>
Cc: "'Yonghong Song'" <yhs@fb.com>,
	"'Toke Høiland-Jørgensen'" <toke@redhat.com>,
	'bpf' <bpf@vger.kernel.org>,
	"'Alexei Starovoitov'" <ast@kernel.org>,
	"'Andrii Nakryiko'" <andrii@kernel.org>,
	"'Daniel Borkmann'" <daniel@iogearbox.net>,
	"'Joanne Koong'" <joannelkoong@gmail.com>,
	"'Jesper Dangaard Brouer'" <brouer@redhat.com>
Subject: Re: [PATCH] bpf: fix rq lock recursion issue
Date: Mon, 13 Jun 2022 14:35:27 -0700	[thread overview]
Message-ID: <006701d87f6d$7fe0a060$7fa1e120$@quicinc.com> (raw)
In-Reply-To: <CAADnVQJUyvhqjnn9OuB=GN=NgA3Wu59fQqLM8nzg_TWh1HnJ4Q@mail.gmail.com>


On 6/13/22 2:01 PM, Alexei Starovoitov wrote:
> is doesn't solve anything.
> Please provide a reproducer.

I'm trying to find an easy way to repro the issue, so far, unsuccessful.

> iirc the task's affinity change can race even with preemption disabled
> on this cpu. Why would s/migrate/preemption/ address the deadlock ?

I don't think task's affinity change races with preemption disabled/enabled.

Switching to preemption disable/enable calls helps as it's just simple
counter increment and decrement with a barrier, but with migrate 
disable/enable when task's affinity changes, we run into recursive bug
due to rq lock.

By the way, migrate disable/enable does end up calling preemt disable/enable
as well, pls see [1].

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/sched/core.c#n2224



  reply	other threads:[~2022-06-13 21:35 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-13  2:52 [PATCH] bpf: fix rq lock recursion issue Satya Durga Srinivasu Prabhala
2022-06-13  9:22 ` Toke Høiland-Jørgensen
2022-06-13 16:17   ` Satya Durga Srinivasu Prabhala
2022-06-13 16:35   ` Yonghong Song
2022-06-13 17:47     ` Satya Durga Srinivasu Prabhala
2022-06-13 21:01       ` Alexei Starovoitov
2022-06-13 21:35         ` Satya Durga Srinivasu Prabhala [this message]
2022-06-13 21:49           ` Alexei Starovoitov
2022-06-14  1:10             ` Satya Durga Srinivasu Prabhala
2022-06-14  6:09               ` Yonghong Song
2022-06-24  6:56                 ` Satya Durga Srinivasu Prabhala
2022-06-24 16:46                   ` Alexei Starovoitov

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