linux-kernel - Re: [PATCH v4 00/15] follow

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Message-ID: <20201029100157.GA10041@infradead.org>
Date:   Thu, 29 Oct 2020 10:01:57 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     Christoph Hellwig <hch@...radead.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        KVM list <kvm@...r.kernel.org>, Linux MM <linux-mm@...ck.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>
Subject: Re: [PATCH v4 00/15] follow_pfn and other iomap races

On Thu, Oct 29, 2020 at 10:38:16AM +0100, Daniel Vetter wrote:
> Hm so Jason and me discussed this, but e.g. the s390 is safe with with
> just the pagetable locks. So we'd need two versions.
> 
> The more practical problem is that I haven't found a reasonable way to
> check that a passed in mmu_notifier is registered against the mm we're
> working on, and without that check it feels a bit silly. But if you
> see how to do that I think we can do an EXPORT_SYMBOL_GPL follow_pfn
> which takes the notifier, and an __follow_pfn for s390 and similar
> internal code which isn't exported.

True, this is a bit of a mess.  So maybe just rename it to __follow_pfn,
proper documentation of the requirements and a switch to
EXPORT_SYMBOL_GPL.