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Subject: Re: [PATCH-tip v6 01/20] locking/rwsem: Prevent decrement of reader
 count before increment
To:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Will Deacon <will.deacon@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        Davidlohr Bueso <dave@stgolabs.net>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        huang ying <huang.ying.caritas@gmail.com>,
        stable@vger.kernel.org
References: <20190428155755.14267-1-longman@redhat.com>
 <20190428155755.14267-2-longman@redhat.com>
From:   Waiman Long <longman@redhat.com>
Organization: Red Hat
Message-ID: <43b4250d-d9b5-a4b6-ee1b-d256ecddd105@redhat.com>
Date:   Sun, 28 Apr 2019 12:07:02 -0400
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On 4/28/19 11:57 AM, Waiman Long wrote:
> During my rwsem testing, it was found that after a down_read(), the
> reader count may occasionally become 0 or even negative. Consequently,
> a writer may steal the lock at that time and execute with the reader
> in parallel thus breaking the mutual exclusion guarantee of the write
> lock. In other words, both readers and writer can become rwsem owners
> simultaneously.

I would like to have this particular patch merged in the next merge
window, if possible, so that I can backport it downstream.

Thanks,
Longman