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Date:   Sun, 28 Apr 2019 12:07:02 -0400
From:   Waiman Long <>
To:     Peter Zijlstra <>,
        Ingo Molnar <>,
        Will Deacon <>,
        Thomas Gleixner <>,
        Borislav Petkov <>,
        "H. Peter Anvin" <>
        Davidlohr Bueso <>,
        Linus Torvalds <>,
        Tim Chen <>,
        huang ying <>,
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.


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