linux-kernel - Re: [GIT PULL] afs: Fixes

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Message-ID: <25484.1511651969@warthog.procyon.org.uk>
Date:   Sat, 25 Nov 2017 23:19:29 +0000
From:   David Howells <dhowells@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     dhowells@...hat.com, linux-afs@...ts.infradead.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] afs: Fixes

Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> However, even when you do that, the page can be writable in other
> mappings. At least fork(), for example, only clears the dirty bit,
> doesn't mark it write-protected.

I assumed the rmap walk done by page_mkclean() would take care of that but I'm
not really clear on what the code does.

> I just hope that the inconsistency isn't fatal to the afs client or
> server code. For example, if you retry writes forever when a checksum
> were to not match the data, that would be bad.

Shouldn't be a problem for the the in-Linux client.  Data is copied into
sk_bufs preparatory to doing further things to it like checksumming,
encryption or transmission (actually, in future, I would like to use the
encryption process to save on the copy, but this shouldn't bother that
either).

AFAIK, the servers are all userspace jobs that don't let anyone else touch
their storage so that they can maintain correctness on the data version number
of each vnode.

> so I just wanted to bring this up as a potential issue, not
> necessarily as a big problem.

Thanks.

David