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

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Message-ID: <20191108020456.sulyjskhq3s5zcaa@linux-p48b>
Date:   Thu, 7 Nov 2019 18:04:56 -0800
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Waiman Long <longman@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        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, 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.

Thanks,
Davidlohr