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

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Message-ID: <nycvar.YSQ.7.76.1710011805070.5407@knanqh.ubzr>
Date:   Sun, 1 Oct 2017 18:29:22 -0400 (EDT)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Christoph Hellwig <hch@...radead.org>
cc:     Alexander Viro <viro@...iv.linux.org.uk>, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-embedded@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Chris Brandt <Chris.Brandt@...esas.com>
Subject: Re: [PATCH v4 4/5] cramfs: add mmap support

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?

Why the special handling on mm->mmap_sem with VM_FAULT_RETRY?

What are the potential problems with my approach I didn't cover yet?

Serious: I'm simply looking for solutions here.

Nicolas