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Wong" , Trond Myklebust , Anna Schumaker , David Hildenbrand , Logan Gunthorpe , linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-nfs@vger.kernel.org, linux-mm@kvack.org, LKML Subject: Re: [PATCH v2 4/7] iov_iter: new iov_iter_pin_pages*() routines Message-ID: References: <20220831041843.973026-1-jhubbard@nvidia.com> <20220831041843.973026-5-jhubbard@nvidia.com> <103fe662-3dc8-35cb-1a68-dda8af95c518@nvidia.com> <20220906102106.q23ovgyjyrsnbhkp@quack3> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1663857123; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=/mtTNf4PXC+ykYPVOfxIiGXI0dE7me4fgbHt4EcB8iA=; b=e9wtwIhgvZ2LMsRHyULm0jtItgzRJrtaymy23nBOglwDxxY+BSThNq0qU/que9aEN0zTOY tREuYNraEwXqW8P35xRrkvrC0rTqHx+m/AfQtOhs12Nw2QJ1RWx/UVOlYCfc8hboX+SBYt NpHdK/dMKwVq7zIKCInQCHuVjOi/aFE= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=infradead.org header.s=bombadil.20210309 header.b=n2t0Tta3; dmarc=none; spf=none (imf28.hostedemail.com: domain of BATV+ecf30307a2904c53da59+6969+infradead.org+hch@bombadil.srs.infradead.org has no SPF policy when checking 198.137.202.133) smtp.mailfrom=BATV+ecf30307a2904c53da59+6969+infradead.org+hch@bombadil.srs.infradead.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1663857123; a=rsa-sha256; cv=none; b=gbSHFuTkJyXcqjHY50m1H83/uZqOAu/Fg0UwbQj141nHmdMJA6rIx/IG28qV0EjW4hY7jN XyRrntbJxtxpWq6g83a2ltsJLW1+ebDWxzlXu1rlwtTPjyWBkau3G2mNKUmIDzLHPEqFSf IZmqI0lALbt7BzJhW0qEh03Zo6x3Omk= Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=infradead.org header.s=bombadil.20210309 header.b=n2t0Tta3; dmarc=none; spf=none (imf28.hostedemail.com: domain of BATV+ecf30307a2904c53da59+6969+infradead.org+hch@bombadil.srs.infradead.org has no SPF policy when checking 198.137.202.133) smtp.mailfrom=BATV+ecf30307a2904c53da59+6969+infradead.org+hch@bombadil.srs.infradead.org X-Rspam-User: X-Stat-Signature: swj7qxkbk7phf7zffsgc19f6tef9e6md X-Rspamd-Queue-Id: AA44AC0021 X-Rspamd-Server: rspam06 X-HE-Tag: 1663857122-417367 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Sep 14, 2022 at 04:51:17AM +0100, Al Viro wrote: > Unless I'm misreading Jan, the question is whether they should get or > pin. And I think the answer is: inside ->read_iter or ->write_iter they should neither get or pin. The callers of it need to pin the pages if they are pagecache pages that can potentially be written to through shared mappings, else a get would be enough. But the method instance should not have to care and just be able to rely on the caller making sure they do not go away. > I'm really tempted to slap > if (WARN_ON(i->data_source)) > return 0; > into copy_to_iter() et.al., along with its opposite for copy_from_iter(). Ys, I think that would be useful. And we could use something more descriptive than READ/WRITE to start with.