linux-kernel - Re: [PATCH] hugetlbfs: Take read_lock on i

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Message-Id: <20191107192202.8869589f225132480d77a33b@linux-foundation.org>
Date:   Thu, 7 Nov 2019 19:22:02 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Davidlohr Bueso <dave@...olabs.net>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Waiman Long <longman@...hat.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH] hugetlbfs: Take read_lock on i_mmap for PMD sharing

On Thu, 7 Nov 2019 18:04:56 -0800 Davidlohr Bueso <dave@...olabs.net> wrote:

> On Thu, 07 Nov 2019, Mike Kravetz wrote:
> 
> >Note that huge_pmd_share now increments the page count with the semaphore
> >held just in read mode.  It is OK to do increments in parallel without
> >synchronization.  However, we don't want anyone else changing the count
> >while that check in huge_pmd_unshare is happening.  Hence, the need for
> >taking the semaphore in write mode.
> 
> This would be a nice addition to the changelog methinks.

Done.