linux-kernel - Re: [PATCH 2/5] coredump: Fix handling of partial writes in dump

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Message-ID: <94141fbb-9559-1851-54c1-cdc5fc529a1a@landley.net>
Date:   Tue, 28 Apr 2020 11:40:47 -0500
From:   Rob Landley <rob@...dley.net>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Jann Horn <jannh@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Mark Salter <msalter@...hat.com>,
        Aurelien Jacquiot <jacquiot.aurelien@...il.com>,
        linux-c6x-dev@...ux-c6x.org,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        Linux-sh list <linux-sh@...r.kernel.org>
Subject: Re: [PATCH 2/5] coredump: Fix handling of partial writes in
 dump_emit()

On 4/27/20 10:35 PM, Linus Torvalds wrote:
> On Mon, Apr 27, 2020 at 8:28 PM Jann Horn <jannh@...gle.com> wrote:
>>
>> After a partial write, we have to update the input buffer pointer.
> 
> Interesting. It seems this partial write case never triggers (except
> for actually killing the core-dump).
> 
> Or did you find a case where it actually matters?
> 
> Your fix is obviously correct, but it also makes me go "that function
> clearly never actually worked for partial writes, maybe we shouldn't
> even bother?"

Writes to a local filesystem should never be short unless disk full/error.

Once upon a time this was yet another thing that NFS could break that no other
filesystem would break, but I dunno about now? (I think the page cache collates
it and defers the flush until the error can't be reported back anyway?)

Rob