linux-kernel - [PATCH AUTOSEL 5.4 013/330] PCI/IOV: Serialize sysfs sriov

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Date:   Thu, 17 Sep 2020 21:55:53 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Pierre Crégut <pierre.cregut@...nge.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Sasha Levin <sashal@...nel.org>, linux-pci@...r.kernel.org
Subject: [PATCH AUTOSEL 5.4 013/330] PCI/IOV: Serialize sysfs sriov_numvfs reads vs writes

From: Pierre Crégut <pierre.cregut@...nge.com>

[ Upstream commit 35ff867b76576e32f34c698ccd11343f7d616204 ]

When sriov_numvfs is being updated, we call the driver->sriov_configure()
function, which may enable VFs and call probe functions, which may make new
devices visible.  This all happens before before sriov_numvfs_store()
updates sriov->num_VFs, so previously, concurrent sysfs reads of
sriov_numvfs returned stale values.

Serialize the sysfs read vs the write so the read returns the correct
num_VFs value.

[bhelgaas: hold device_lock instead of checking mutex_is_locked()]
Link: https://bugzilla.kernel.org/show_bug.cgi?id=202991
Link: https://lore.kernel.org/r/20190911072736.32091-1-pierre.cregut@orange.com
Signed-off-by: Pierre Crégut <pierre.cregut@...nge.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/pci/iov.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
index deec9f9e0b616..9c116cbaa95d8 100644
--- a/drivers/pci/iov.c
+++ b/drivers/pci/iov.c
@@ -253,8 +253,14 @@ 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 sprintf(buf, "%u\n", pdev->sriov->num_VFs);
+	return sprintf(buf, "%u\n", num_vfs);
 }
 
 /*
-- 
2.25.1