linux-kernel - Re: [PATCH v4 4/5] cramfs: add mmap support

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Message-ID: <CAFLxGvzfQrvU-8w7F26mez6fCQD+iS_qRJpLSU+2DniEGouEfA@mail.gmail.com>
Date:   Tue, 3 Oct 2017 00:45:27 +0200
From:   Richard Weinberger <richard.weinberger@...il.com>
To:     Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "linux-embedded@...r.kernel.org" <linux-embedded@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Chris Brandt <Chris.Brandt@...esas.com>
Subject: Re: [PATCH v4 4/5] cramfs: add mmap support

On Mon, Oct 2, 2017 at 12:29 AM, Nicolas Pitre <nicolas.pitre@...aro.org> wrote:
> On Sun, 1 Oct 2017, Christoph Hellwig wrote:
>
>> up_read(&mm->mmap_sem) in the fault path is a still a complete
>> no-go,
>>
>> NAK
>
> Care to elaborate?
>
> What about mm/filemap.c:__lock_page_or_retry() then?

As soon you up_read() in the page fault path other tasks will race
with you before
you're able to grab the write lock.

HTH

-- 
Thanks,
//richard