From: Jason Gunthorpe <jgg@nvidia.com>
To: Leon Romanovsky <leon@kernel.org>
Cc: "Alex Williamson" <alex@shazbot.org>,
"Matt Evans" <matt@ozlabs.org>, "Alex Mastro" <amastro@fb.com>,
"Christian König" <christian.koenig@amd.com>,
"Bjorn Helgaas" <bhelgaas@google.com>,
"Logan Gunthorpe" <logang@deltatee.com>,
"Kevin Tian" <kevin.tian@intel.com>,
"Pranjal Shrivastava" <praan@google.com>,
"Longfang Liu" <liulongfang@huawei.com>,
"Mahmoud Adam" <mngyadam@amazon.de>,
"David Matlack" <dmatlack@google.com>,
"Björn Töpel" <bjorn@kernel.org>,
"Sumit Semwal" <sumit.semwal@linaro.org>,
"Ankit Agrawal" <ankita@nvidia.com>,
"Alistair Popple" <apopple@nvidia.com>,
"Vivek Kasireddy" <vivek.kasireddy@intel.com>,
linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org,
kvm@vger.kernel.org, linux-pci@vger.kernel.org
Subject: Re: [PATCH v5 1/9] PCI/P2PDMA: Split pool-related cleanup out of pci_p2pdma_release()
Date: Tue, 4 Aug 2026 21:31:27 -0300 [thread overview]
Message-ID: <20260805003127.GJ27883@nvidia.com> (raw)
In-Reply-To: <20260729100840.GM12003@unreal>
On Wed, Jul 29, 2026 at 01:08:40PM +0300, Leon Romanovsky wrote:
> I remember this concern when I wrote the patches and wanted to remove
> RCU entirely. I revisited the Sashiko report, but reached the same
> conclusion again.
>
> The "bug" reported by Sashiko does not exist. The two-layer split
> ensures that p2p is bound to the driver's lifecycle. As a result,
> pdev->p2pdma is assigned and cleared only once during the lifetime of
> pdev.
>
> In this case, the RCU primitives are effectively NOPs, since nothing
> will ever update that pointer.
This sounds right to me too.
The lowest layer has no need of RCU at all, it just remains RCU
because the genalloc layer wants it as part of its locking scheme.
So long as the genalloc gets the synchronize_rcu on destruction there
is no bug.
Jason
next prev parent reply other threads:[~2026-08-05 0:31 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-15 17:47 [PATCH v5 0/9] vfio/pci: Add mmap() for DMABUFs Matt Evans
2026-07-15 17:47 ` [PATCH v5 1/9] PCI/P2PDMA: Split pool-related cleanup out of pci_p2pdma_release() Matt Evans
2026-07-15 18:05 ` sashiko-bot
2026-07-17 8:02 ` Tian, Kevin
2026-07-28 22:33 ` Alex Williamson
2026-07-29 10:08 ` Leon Romanovsky
2026-08-05 0:31 ` Jason Gunthorpe [this message]
2026-07-30 16:45 ` Pranjal Shrivastava
2026-07-15 17:47 ` [PATCH v5 2/9] PCI/P2PDMA: Add CONFIG_PCI_P2PDMA_CORE Matt Evans
2026-07-15 18:03 ` sashiko-bot
2026-07-17 8:02 ` Tian, Kevin
2026-07-30 19:37 ` Pranjal Shrivastava
2026-08-04 15:42 ` Matt Evans
2026-08-04 16:19 ` Logan Gunthorpe
2026-08-05 0:39 ` Jason Gunthorpe
2026-08-05 16:28 ` Matt Evans
2026-08-05 16:40 ` Jason Gunthorpe
2026-08-05 20:50 ` Logan Gunthorpe
2026-07-15 17:47 ` [PATCH v5 3/9] vfio/pci: Add a helper to look up PFNs for DMABUFs Matt Evans
2026-07-15 18:08 ` sashiko-bot
2026-07-17 8:02 ` Tian, Kevin
2026-07-29 17:52 ` Alex Williamson
2026-07-30 17:34 ` Matt Evans
2026-07-30 22:55 ` Pranjal Shrivastava
2026-07-31 17:43 ` Matt Evans
2026-08-03 18:22 ` Matt Evans
2026-08-04 19:01 ` Pranjal Shrivastava
2026-08-05 0:41 ` Jason Gunthorpe
2026-07-15 17:47 ` [PATCH v5 4/9] vfio/pci: Add a helper to create a DMABUF for a BAR-map VMA Matt Evans
2026-07-15 18:12 ` sashiko-bot
2026-07-27 13:45 ` Matt Evans
2026-07-15 17:47 ` [PATCH v5 5/9] vfio/pci: Convert BAR mmap() to use a DMABUF Matt Evans
2026-07-15 18:13 ` sashiko-bot
2026-07-27 13:45 ` Matt Evans
2026-07-15 17:47 ` [PATCH v5 6/9] vfio/pci: Provide a user-facing name for BAR mappings Matt Evans
2026-07-15 18:01 ` sashiko-bot
2026-07-17 8:03 ` Tian, Kevin
2026-07-29 17:52 ` Alex Williamson
2026-07-30 14:37 ` Matt Evans
2026-07-15 17:47 ` [PATCH v5 7/9] vfio/pci: Clean up BAR zap and revocation Matt Evans
2026-07-15 18:00 ` sashiko-bot
2026-07-17 8:03 ` Tian, Kevin
2026-07-29 17:52 ` Alex Williamson
2026-07-30 14:47 ` Matt Evans
2026-08-04 20:10 ` Alex Williamson
2026-08-05 13:58 ` Matt Evans
2026-07-30 23:20 ` Pranjal Shrivastava
2026-07-15 17:47 ` [PATCH v5 8/9] vfio/pci: Support mmap() of a VFIO DMABUF Matt Evans
2026-07-15 18:17 ` sashiko-bot
2026-07-17 8:03 ` Tian, Kevin
2026-07-30 23:33 ` Pranjal Shrivastava
2026-07-15 17:47 ` [PATCH v5 9/9] vfio/pci: Permanently revoke a DMABUF on request Matt Evans
2026-07-15 18:11 ` sashiko-bot
2026-07-27 13:45 ` Matt Evans
2026-07-17 8:03 ` Tian, Kevin
2026-07-30 23:43 ` Pranjal Shrivastava
2026-07-15 18:12 ` [PATCH v5 0/9] vfio/pci: Add mmap() for DMABUFs David Matlack
2026-07-16 14:51 ` Matt Evans
2026-07-16 21:23 ` David Matlack
2026-07-17 8:42 ` David Laight
2026-07-17 16:30 ` David Matlack
2026-07-17 17:12 ` Matt Evans
2026-07-20 21:50 ` David Matlack
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