From: "Christian König" <christian.koenig@amd.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>,
Pavel Begunkov <asml.silence@gmail.com>,
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Praveen Kaligineedi <pkaligineedi@google.com>
Subject: Re: [PATCH net-next v10 02/14] net: page_pool: create hooks for custom page providers
Date: Tue, 11 Jun 2024 10:21:49 +0200 [thread overview]
Message-ID: <924d9411-ce3d-4cf3-889c-379927167d60@amd.com> (raw)
In-Reply-To: <ZmftwZDXYk53fKzm@infradead.org>
Am 11.06.24 um 08:25 schrieb Christoph Hellwig:
> On Mon, Jun 10, 2024 at 02:38:18PM +0200, Christian König wrote:
>> Well there is the fundamental problem that you can't use io_uring to
>> implement the semantics necessary for a dma_fence.
> What is the exact problem there?
It's an intentional design decision that dma_fences can be waited on
with quite a bunch of locks held. Including the DMA-buf reservation
lock, mmap lock, anything page fault related, shrinker etc...
When you give userspace control over the signaling of a dma_fence then
that has the same effect as returning to userspace with those locks held
- you can basically trivially deadlock the system.
I think nearly a dozen implementations fell into that trap:
https://www.kernel.org/doc/html/v5.9/driver-api/dma-buf.html#indefinite-dma-fences
It's well understood and documented by now why this approach doesn't
work. So not much of an issue any more, we just have to reject
implementations from time to time which try doing the same thing again.
Regards,
Christian.
next prev parent reply other threads:[~2024-06-11 8:22 UTC|newest]
Thread overview: 71+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-30 20:15 [PATCH net-next v10 00/14] Device Memory TCP Mina Almasry
2024-05-30 20:16 ` [PATCH net-next v10 01/14] netdev: add netdev_rx_queue_restart() Mina Almasry
2024-05-30 23:51 ` David Wei
2024-06-03 12:52 ` Pavel Begunkov
2024-05-30 20:16 ` [PATCH net-next v10 02/14] net: page_pool: create hooks for custom page providers Mina Almasry
2024-06-01 5:35 ` Christoph Hellwig
2024-06-03 14:17 ` Mina Almasry
2024-06-03 14:52 ` Pavel Begunkov
2024-06-03 15:43 ` Mina Almasry
2024-06-07 13:42 ` Pavel Begunkov
2024-06-07 14:27 ` David Ahern
2024-06-07 14:52 ` Jason Gunthorpe
2024-06-10 0:37 ` David Wei
2024-06-10 1:07 ` Pavel Begunkov
2024-06-10 12:16 ` Jason Gunthorpe
2024-06-10 12:38 ` Christian König
2024-06-10 15:41 ` Mina Almasry
2024-06-10 19:32 ` Pavel Begunkov
2024-06-10 16:22 ` Daniel Vetter
2024-06-11 6:25 ` Christoph Hellwig
2024-06-11 8:21 ` Christian König [this message]
2024-06-10 15:16 ` David Ahern
2024-06-10 19:20 ` Pavel Begunkov
2024-06-10 22:15 ` Jason Gunthorpe
2024-06-11 18:09 ` Mina Almasry
2024-06-12 12:06 ` Jason Gunthorpe
2024-06-12 15:47 ` David Ahern
2024-06-17 19:15 ` Pavel Begunkov
2024-06-11 6:26 ` Christoph Hellwig
2024-06-11 17:48 ` Mina Almasry
2024-06-07 15:42 ` Pavel Begunkov
2024-06-07 15:46 ` Pavel Begunkov
2024-06-07 16:59 ` Mina Almasry
2024-06-10 1:12 ` Pavel Begunkov
2024-06-10 0:27 ` David Wei
2024-06-05 8:24 ` Christoph Hellwig
2024-06-07 13:45 ` Pavel Begunkov
2024-06-11 6:34 ` Christoph Hellwig
2024-06-17 18:04 ` Pavel Begunkov
2024-06-18 6:43 ` Christoph Hellwig
2024-06-18 11:40 ` Pavel Begunkov
2024-06-05 8:23 ` Christoph Hellwig
2024-05-30 20:16 ` [PATCH net-next v10 03/14] net: netdev netlink api to bind dma-buf to a net device Mina Almasry
2024-05-30 20:16 ` [PATCH net-next v10 04/14] netdev: support binding dma-buf to netdevice Mina Almasry
2024-05-30 20:16 ` [PATCH net-next v10 05/14] netdev: netdevice devmem allocator Mina Almasry
2024-06-04 10:13 ` Paolo Abeni
2024-06-04 16:15 ` Steven Rostedt
2024-06-04 16:31 ` Jason Gunthorpe
2024-06-04 16:42 ` Steven Rostedt
2024-06-04 23:44 ` Andrew Lunn
2024-06-05 0:27 ` Steven Rostedt
2024-06-05 0:52 ` Andrew Lunn
2024-06-06 1:43 ` Steven Rostedt
2024-06-07 7:55 ` Niklas Schnelle
2024-05-30 20:16 ` [PATCH net-next v10 06/14] page_pool: convert to use netmem Mina Almasry
2024-06-04 10:23 ` Paolo Abeni
2024-06-06 1:48 ` Steven Rostedt
2024-06-07 12:31 ` Pavel Begunkov
2024-05-30 20:16 ` [PATCH net-next v10 07/14] page_pool: devmem support Mina Almasry
2024-05-30 20:16 ` [PATCH net-next v10 08/14] memory-provider: dmabuf devmem memory provider Mina Almasry
2024-05-30 20:16 ` [PATCH net-next v10 09/14] net: support non paged skb frags Mina Almasry
2024-05-30 20:16 ` [PATCH net-next v10 10/14] net: add support for skbs with unreadable frags Mina Almasry
2024-06-04 10:46 ` Paolo Abeni
2024-06-06 16:49 ` Mina Almasry
2024-06-06 16:58 ` Mina Almasry
2024-05-30 20:16 ` [PATCH net-next v10 11/14] tcp: RX path for devmem TCP Mina Almasry
2024-06-04 10:53 ` Paolo Abeni
2024-05-30 20:16 ` [PATCH net-next v10 12/14] net: add SO_DEVMEM_DONTNEED setsockopt to release RX frags Mina Almasry
2024-05-30 20:16 ` [PATCH net-next v10 13/14] net: add devmem TCP documentation Mina Almasry
2024-06-01 13:09 ` Bagas Sanjaya
2024-05-30 20:16 ` [PATCH net-next v10 14/14] selftests: add ncdevmem, netcat for devmem TCP Mina Almasry
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