From: Al Viro <viro@zeniv.linux.org.uk>
To: David Howells <dhowells@redhat.com>
Cc: David Hildenbrand <david@redhat.com>,
Christoph Hellwig <hch@infradead.org>,
Matthew Wilcox <willy@infradead.org>,
Jens Axboe <axboe@kernel.dk>, Jan Kara <jack@suse.cz>,
Jeff Layton <jlayton@kernel.org>,
Jason Gunthorpe <jgg@nvidia.com>,
Logan Gunthorpe <logang@deltatee.com>,
linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Christoph Hellwig <hch@lst.de>,
John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH v11 2/8] iov_iter: Add a function to extract a page list from an iterator
Date: Fri, 27 Jan 2023 00:52:38 +0000 [thread overview]
Message-ID: <Y9MgVsrMdgGsxNHC@ZenIV> (raw)
In-Reply-To: <2907150.1674777410@warthog.procyon.org.uk>
On Thu, Jan 26, 2023 at 11:56:50PM +0000, David Howells wrote:
> Al says that pinning a page (ie. FOLL_PIN) could cause a deadlock if a page is
> vmspliced into a pipe with the pipe holding a pin on it because pinned pages
> are removed from all page tables. Is this actually the case? I can't see
> offhand where in mm/gup.c it does this.
It doesn't; sorry, really confused memories of what's going on, took a while
to sort them out (FWIW, writeback is where we unmap and check if page is
pinned, while pin_user_pages running into an unmapped page will end up
with handle_mm_fault() (->fault(), actually) try to get the sucker locked
and block on that until the writeback is over).
Said that, I still think that pinned pages (arbitrary pagecache ones,
at that) ending up in a pipe is a seriously bad idea. It's trivial to
arrange for them to stay that way indefinitely - no priveleges needed,
very few limits, etc.
next prev parent reply other threads:[~2023-01-27 0:52 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-26 14:16 [PATCH v11 0/8] iov_iter: Improve page extraction (pin or just list) David Howells
2023-01-26 14:16 ` [PATCH v11 1/8] iov_iter: Define flags to qualify page extraction David Howells
2023-01-26 21:54 ` Al Viro
2023-01-26 23:45 ` David Hildenbrand
2023-01-26 14:16 ` [PATCH v11 2/8] iov_iter: Add a function to extract a page list from an iterator David Howells
2023-01-26 21:59 ` Al Viro
2023-01-26 22:36 ` Al Viro
2023-01-26 22:49 ` John Hubbard
2023-01-26 23:44 ` David Hildenbrand
2023-01-27 2:02 ` Al Viro
2023-01-27 12:30 ` Jan Kara
2023-01-27 12:34 ` David Hildenbrand
2023-01-26 23:56 ` David Howells
2023-01-27 0:10 ` David Hildenbrand
2023-01-27 0:52 ` Al Viro [this message]
2023-01-27 1:21 ` Al Viro
2023-01-27 12:38 ` Jan Kara
2023-01-26 14:16 ` [PATCH v11 3/8] iomap: Don't get an reference on ZERO_PAGE for direct I/O block zeroing David Howells
2023-01-26 15:12 ` Christoph Hellwig
2023-01-26 14:16 ` [PATCH v11 4/8] block: Fix bio_flagged() so that gcc can better optimise it David Howells
2023-01-26 14:16 ` [PATCH v11 5/8] block: Replace BIO_NO_PAGE_REF with BIO_PAGE_REFFED with inverted logic David Howells
2023-01-26 14:16 ` [PATCH v11 6/8] block: Add BIO_PAGE_PINNED and associated infrastructure David Howells
2023-01-26 14:16 ` [PATCH v11 7/8] block: Convert bio_iov_iter_get_pages to use iov_iter_extract_pages David Howells
2023-01-26 14:16 ` [PATCH v11 8/8] block: convert bio_map_user_iov " David Howells
2023-01-30 7:41 ` [PATCH v11 0/8] iov_iter: Improve page extraction (pin or just list) Naresh Kamboju
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