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From: Qian Cai <cai@lca.pw>
To: Marco Elver <elver@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Will Deacon <will@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	"paul E. McKenney" <paulmck@kernel.org>,
	kasan-dev <kasan-dev@googlegroups.com>
Subject: Re: [PATCH] locking/osq_lock: fix a data race in osq_wait_next
Date: Tue, 28 Jan 2020 07:53:00 -0500
Message-ID: <C50F23AD-7CCA-423B-9C13-E06596CB4399@lca.pw> (raw)
In-Reply-To: <CANpmjNNo6yW-y-Af7JgvWi3t==+=02hE4-pFU4OiH8yvbT3Byg@mail.gmail.com>



> On Jan 28, 2020, at 6:46 AM, Marco Elver <elver@google.com> wrote:
> 
> Qian: firstly I suggest you try
> CONFIG_KCSAN_REPORT_ONCE_IN_MS=1000000000 as mentioned before so your
> system doesn't get spammed, considering you do not use the default
> config but want to use all debugging tools at once which seems to
> trigger certain data races more than usual.

Yes, I had that. There are still many reports that I plan to look at them one by one. It takes so much time that cause systemd storage lookup timeouts and I needed to manually get out of the emergency shell.

> 
> Secondly, what are your expectations? If you expect the situation to
> be perfect tomorrow, you'll be disappointed. This is inherent, given
> the problem we face (safe concurrency). Consider the various parts to
> this story: concurrent kernel code, the LKMM, people's preferences and
> opinions, and KCSAN (which is late to the party). All of them are
> still evolving, hopefully together. At least that's my expectation.

I’ll try to reduce splats as many as possible by any data_race(), disable the whole file or actually fix it. Any resolved splat will hurt the ability to find the real data races at some degrees.

> 
> What to do about osq_lock here? If people agree that no further
> annotations are wanted, and the reasoning above concludes there are no
> bugs, we can blacklist the file. That would, however, miss new data
> races in future.

This is a question to locking maintainers. data_race() macro sounds reasonable to me, but blacklisted the file is still better than leaving it as-is.

  reply index

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-22 16:38 Qian Cai
2020-01-22 16:59 ` Will Deacon
2020-01-22 17:08   ` Qian Cai
2020-01-22 22:38     ` Marco Elver
2020-01-22 23:54       ` Qian Cai
2020-01-23  9:39         ` Peter Zijlstra
2020-01-28  3:11           ` Qian Cai
2020-01-28 11:46             ` Marco Elver
2020-01-28 12:53               ` Qian Cai [this message]
2020-01-28 16:52               ` Peter Zijlstra
2020-01-28 16:56               ` Peter Zijlstra
2020-01-29  0:22                 ` Paul E. McKenney
2020-01-29 15:29                   ` Marco Elver
2020-01-29 18:40                     ` Peter Zijlstra
2020-01-30 13:39                       ` Marco Elver
2020-01-30 13:48                         ` Peter Zijlstra
2020-01-31  3:32                           ` Qian Cai
2020-01-29 18:49                   ` Peter Zijlstra
2020-01-29 19:26                     ` Paul E. McKenney
2020-01-23  9:36       ` Peter Zijlstra
2020-01-28  3:12         ` Qian Cai
2020-01-28  8:18           ` Marco Elver
2020-01-28 10:10             ` Qian Cai
2020-01-28 10:29               ` Marco Elver
2020-01-22 17:09 ` Peter Zijlstra

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