From: Jim Harris <jim.harris@samsung.com>
To: Bjorn Helgaas <bhelgaas@google.com>,
"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Leon Romanovsky <leonro@nvidia.com>,
"Jason Gunthorpe" <jgg@nvidia.com>,
Alex Williamson <alex.williamson@redhat.com>,
"pierre.cregut@orange.com" <pierre.cregut@orange.com>
Subject: [PATCH v2 1/2] PCI/IOV: Revert "PCI/IOV: Serialize sysfs sriov_numvfs reads vs writes"
Date: Fri, 9 Feb 2024 23:52:12 +0000 [thread overview]
Message-ID: <170752273224.1693615.11371097645648272257.stgit@bgt-140510-bm01.eng.stellus.in> (raw)
In-Reply-To: <170752254154.1693615.9176696143128338408.stgit@bgt-140510-bm01.eng.stellus.in>
If an SR-IOV enabled device is held by vfio, and the device is removed,
vfio will hold device lock and notify userspace of the removal. If
userspace reads the sriov_numvfs sysfs entry, that thread will be blocked
since sriov_numvfs_show() also tries to acquire the device lock. If that
same thread is responsible for releasing the device to vfio, it results in
a deadlock.
The proper way to detect a change to the num_VFs value is to listen for a
sysfs event, not to add a device_lock() on the attribute _show() in the
kernel.
This reverts commit 35ff867b76576e32f34c698ccd11343f7d616204.
Revert had a small conflict, the sprintf() is now changed to sysfs_emit().
Link: https://lore.kernel.org/linux-pci/ZXJI5+f8bUelVXqu@ubuntu/
Suggested-by: Leon Romanovsky <leonro@nvidia.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jim Harris <jim.harris@samsung.com>
---
drivers/pci/iov.c | 8 +-------
1 file changed, 1 insertion(+), 7 deletions(-)
diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
index aaa33e8dc4c9..0ca20cd518d5 100644
--- a/drivers/pci/iov.c
+++ b/drivers/pci/iov.c
@@ -395,14 +395,8 @@ static ssize_t sriov_numvfs_show(struct device *dev,
char *buf)
{
struct pci_dev *pdev = to_pci_dev(dev);
- u16 num_vfs;
-
- /* Serialize vs sriov_numvfs_store() so readers see valid num_VFs */
- device_lock(&pdev->dev);
- num_vfs = pdev->sriov->num_VFs;
- device_unlock(&pdev->dev);
- return sysfs_emit(buf, "%u\n", num_vfs);
+ return sysfs_emit(buf, "%u\n", pdev->sriov->num_VFs);
}
/*
next prev parent reply other threads:[~2024-02-09 23:52 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20240209235208uscas1p26c658c64cc85711cd3aa6312224164fc@uscas1p2.samsung.com>
2024-02-09 23:52 ` [PATCH v2 0/2] PCI/IOV: sriov_numvfs bug fixes Jim Harris
[not found] ` <CGME20240209235213uscas1p2e8de2bdf05e6e7cba51bd41ddb42a8e4@uscas1p2.samsung.com>
2024-02-09 23:52 ` Jim Harris [this message]
2024-02-10 3:20 ` [PATCH v2 1/2] PCI/IOV: Revert "PCI/IOV: Serialize sysfs sriov_numvfs reads vs writes" Kuppuswamy Sathyanarayanan
2024-02-11 8:48 ` Leon Romanovsky
2024-02-11 19:15 ` Kuppuswamy Sathyanarayanan
2024-02-12 9:31 ` Leon Romanovsky
2024-02-12 20:27 ` Bjorn Helgaas
[not found] ` <CGME20240212225904uscas1p19a3d7743607a0abe3627fb8c4829f27b@uscas1p1.samsung.com>
2024-02-12 22:59 ` Jim Harris
2024-02-13 7:37 ` Leon Romanovsky
2024-02-13 9:40 ` pierre.cregut
2024-02-13 14:59 ` Jason Gunthorpe
2024-02-13 7:34 ` Leon Romanovsky
2024-02-13 15:59 ` Bjorn Helgaas
2024-02-13 17:46 ` Leon Romanovsky
2024-02-13 18:00 ` Kuppuswamy Sathyanarayanan
2024-02-13 19:45 ` Bjorn Helgaas
2024-02-14 7:16 ` Leon Romanovsky
[not found] ` <CGME20240214170409uscas1p1e04d5916cb91670ea7f6413f0347d9ca@uscas1p1.samsung.com>
2024-02-14 17:04 ` Jim Harris
2024-02-14 17:50 ` Bjorn Helgaas
[not found] ` <CGME20240214225538uscas1p2d6502c3bd144e4d90d4506acf4847159@uscas1p2.samsung.com>
2024-02-14 22:55 ` Jim Harris
[not found] ` <CGME20240209235218uscas1p2d0978af6623037fa1b9358a2ad2320c5@uscas1p2.samsung.com>
2024-02-09 23:52 ` [PATCH v2 2/2] pci/iov: fix kobject_uevent() ordering in sriov_enable() Jim Harris
2024-02-10 3:22 ` Kuppuswamy Sathyanarayanan
2024-02-12 15:17 ` Keith Busch
2024-02-12 15:29 ` Leon Romanovsky
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