From: Christoph Hellwig <hch@infradead.org>
To: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@infradead.org>,
John Hubbard <jhubbard@nvidia.com>,
Andrew Morton <akpm@linux-foundation.org>,
Jens Axboe <axboe@kernel.dk>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Miklos Szeredi <miklos@szeredi.hu>,
"Darrick J . Wong" <djwong@kernel.org>,
Trond Myklebust <trond.myklebust@hammerspace.com>,
Anna Schumaker <anna@kernel.org>,
David Hildenbrand <david@redhat.com>,
Logan Gunthorpe <logang@deltatee.com>,
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 <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 4/7] iov_iter: new iov_iter_pin_pages*() routines
Date: Wed, 7 Sep 2022 01:45:26 -0700 [thread overview]
Message-ID: <YxhaJktqtHw3QTSG@infradead.org> (raw)
In-Reply-To: <20220906102106.q23ovgyjyrsnbhkp@quack3>
On Tue, Sep 06, 2022 at 12:21:06PM +0200, Jan Kara wrote:
> > For FOLL_PIN callers, never pin bvec and kvec pages: For file systems
> > not acquiring a reference is obviously safe, and the other callers will
> > need an audit, but I can't think of why it woul ever be unsafe.
>
> Are you sure about "For file systems not acquiring a reference is obviously
> safe"? I can see places e.g. in orangefs, afs, etc. which create bvec iters
> from pagecache pages. And then we have iter_file_splice_write() which
> creates bvec from pipe pages (which can also be pagecache pages if
> vmsplice() is used). So perhaps there are no lifetime issues even without
> acquiring a reference (but looking at the code I would not say it is
> obvious) but I definitely don't see how it would be safe to not get a pin
> to signal to filesystem backing the pagecache page that there is DMA
> happening to/from the page.
I mean in the context of iov_iter_get_pages callers, that is direct
I/O. Direct callers of iov_iter_bvec which then pass that iov to
->read_iter / ->write_iter will need to hold references (those are
the references that the callers of iov_iter_get_pages rely on!).
next prev parent reply other threads:[~2022-09-07 8:45 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-31 4:18 [PATCH v2 0/7] convert most filesystems to pin_user_pages_fast() John Hubbard
2022-08-31 4:18 ` [PATCH v2 1/7] mm: change release_pages() to use unsigned long for npages John Hubbard
2022-08-31 4:18 ` [PATCH v2 2/7] mm/gup: introduce pin_user_page() John Hubbard
2022-09-06 6:37 ` Christoph Hellwig
2022-09-06 7:12 ` John Hubbard
2022-08-31 4:18 ` [PATCH v2 3/7] block: add dio_w_*() wrappers for pin, unpin user pages John Hubbard
2022-08-31 4:18 ` [PATCH v2 4/7] iov_iter: new iov_iter_pin_pages*() routines John Hubbard
2022-09-01 0:42 ` Al Viro
2022-09-01 1:48 ` John Hubbard
2022-09-06 6:47 ` Christoph Hellwig
2022-09-06 7:44 ` John Hubbard
2022-09-06 7:48 ` Christoph Hellwig
2022-09-06 7:58 ` John Hubbard
2022-09-07 8:50 ` Christoph Hellwig
2022-09-06 10:21 ` Jan Kara
2022-09-07 8:45 ` Christoph Hellwig [this message]
2022-09-14 3:51 ` Al Viro
2022-09-14 14:52 ` Jan Kara
2022-09-14 16:42 ` Al Viro
2022-09-15 8:16 ` Jan Kara
2022-09-16 1:55 ` Al Viro
2022-09-20 5:02 ` Al Viro
2022-09-22 14:36 ` Christoph Hellwig
2022-09-22 14:43 ` David Hildenbrand
2022-09-22 14:45 ` Christoph Hellwig
2022-09-22 2:22 ` Al Viro
2022-09-22 6:09 ` John Hubbard
2022-09-22 11:29 ` Jan Kara
2022-09-23 3:19 ` Al Viro
2022-09-23 4:05 ` John Hubbard
2022-09-23 8:39 ` Christoph Hellwig
2022-09-23 12:22 ` Jan Kara
2022-09-23 4:34 ` John Hubbard
2022-09-22 14:38 ` Christoph Hellwig
2022-09-23 4:22 ` Al Viro
2022-09-23 8:44 ` Christoph Hellwig
2022-09-23 16:13 ` Al Viro
2022-09-26 15:53 ` Christoph Hellwig
2022-09-26 19:55 ` Al Viro
2022-09-22 14:31 ` Christoph Hellwig
2022-09-22 14:36 ` Al Viro
2022-08-31 4:18 ` [PATCH v2 5/7] block, bio, fs: convert most filesystems to pin_user_pages_fast() John Hubbard
2022-09-06 6:48 ` Christoph Hellwig
2022-09-06 7:15 ` John Hubbard
2022-08-31 4:18 ` [PATCH v2 6/7] NFS: direct-io: convert to FOLL_PIN pages John Hubbard
2022-09-06 6:49 ` Christoph Hellwig
2022-09-06 7:16 ` John Hubbard
2022-08-31 4:18 ` [PATCH v2 7/7] fuse: convert direct IO paths to use FOLL_PIN John Hubbard
2022-08-31 10:37 ` Miklos Szeredi
2022-09-01 1:33 ` John Hubbard
2022-09-06 6:36 ` [PATCH v2 0/7] convert most filesystems to pin_user_pages_fast() Christoph Hellwig
2022-09-06 7:10 ` John Hubbard
2022-09-06 7:22 ` Christoph Hellwig
2022-09-06 7:37 ` John Hubbard
2022-09-06 7:46 ` Christoph Hellwig
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