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    Subject[PATCH 5.4 012/388] PCI/IOV: Serialize sysfs sriov_numvfs reads vs writes
    Date
    From: Pierre Crégut <pierre.cregut@orange.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@orange.com>
    Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
    Signed-off-by: Sasha Levin <sashal@kernel.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


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