linux-kernel - Re: [PATCH-tip v6 01/20] locking/rwsem: Prevent decrement of reader count before increment

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Date:   Sun, 28 Apr 2019 12:07:02 -0400
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Davidlohr Bueso <dave@...olabs.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        huang ying <huang.ying.caritas@...il.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH-tip v6 01/20] locking/rwsem: Prevent decrement of reader
 count before increment

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