linux-kernel - Re: [PATCH v3 4/5] cramfs: add mmap support

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Message-ID: <nycvar.YSQ.7.76.1708311343060.2606@knanqh.ubzr>
Date:   Thu, 31 Aug 2017 13:52:35 -0400 (EDT)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Christoph Hellwig <hch@...radead.org>
cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-embedded@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Chris Brandt <Chris.Brandt@...esas.com>, linux-mm@...ck.org
Subject: Re: [PATCH v3 4/5] cramfs: add mmap support

On Thu, 31 Aug 2017, Christoph Hellwig wrote:

> The whole VMA games here look entirely bogus  you can't just drop
> and reacquire mmap_sem for example.
> And splitting vmas looks just
> as promblematic.

I didn't just decide to do that on a whim. I spent quite some time 
looking at page fault code paths and make sure it is fine to reaquire 
the lock. There are existing code paths that drop the lock entirely and 
return with no locks so this is already expected by the core code.

> As a minimum you really must see the linux-mm list can get some
> feedback there.

Good point. You added linux-mm to CC so I'll wait for their comments.

Nicolas