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    Subject[PATCH 5.15 170/667] PCI: Avoid pci_dev_lock() AB/BA deadlock with sriov_numvfs_store()
    Date
    From: Yicong Yang <yangyicong@hisilicon.com>

    [ Upstream commit a91ee0e9fca9d7501286cfbced9b30a33e52740a ]

    The sysfs sriov_numvfs_store() path acquires the device lock before the
    config space access lock:

    sriov_numvfs_store
    device_lock # A (1) acquire device lock
    sriov_configure
    vfio_pci_sriov_configure # (for example)
    vfio_pci_core_sriov_configure
    pci_disable_sriov
    sriov_disable
    pci_cfg_access_lock
    pci_wait_cfg # B (4) wait for dev->block_cfg_access == 0

    Previously, pci_dev_lock() acquired the config space access lock before the
    device lock:

    pci_dev_lock
    pci_cfg_access_lock
    dev->block_cfg_access = 1 # B (2) set dev->block_cfg_access = 1
    device_lock # A (3) wait for device lock

    Any path that uses pci_dev_lock(), e.g., pci_reset_function(), may
    deadlock with sriov_numvfs_store() if the operations occur in the sequence
    (1) (2) (3) (4).

    Avoid the deadlock by reversing the order in pci_dev_lock() so it acquires
    the device lock before the config space access lock, the same as the
    sriov_numvfs_store() path.

    [bhelgaas: combined and adapted commit log from Jay Zhou's independent
    subsequent posting:
    https://lore.kernel.org/r/20220404062539.1710-1-jianjay.zhou@huawei.com]
    Link: https://lore.kernel.org/linux-pci/1583489997-17156-1-git-send-email-yangyicong@hisilicon.com/
    Also-posted-by: Jay Zhou <jianjay.zhou@huawei.com>
    Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
    Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/pci/pci.c | 10 +++++-----
    1 file changed, 5 insertions(+), 5 deletions(-)

    diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
    index 0380543d10fd..09815cbc18f9 100644
    --- a/drivers/pci/pci.c
    +++ b/drivers/pci/pci.c
    @@ -5079,18 +5079,18 @@ static int pci_reset_bus_function(struct pci_dev *dev, bool probe)

    static void pci_dev_lock(struct pci_dev *dev)
    {
    - pci_cfg_access_lock(dev);
    /* block PM suspend, driver probe, etc. */
    device_lock(&dev->dev);
    + pci_cfg_access_lock(dev);
    }

    /* Return 1 on successful lock, 0 on contention */
    int pci_dev_trylock(struct pci_dev *dev)
    {
    - if (pci_cfg_access_trylock(dev)) {
    - if (device_trylock(&dev->dev))
    + if (device_trylock(&dev->dev)) {
    + if (pci_cfg_access_trylock(dev))
    return 1;
    - pci_cfg_access_unlock(dev);
    + device_unlock(&dev->dev);
    }

    return 0;
    @@ -5099,8 +5099,8 @@ EXPORT_SYMBOL_GPL(pci_dev_trylock);

    void pci_dev_unlock(struct pci_dev *dev)
    {
    - device_unlock(&dev->dev);
    pci_cfg_access_unlock(dev);
    + device_unlock(&dev->dev);
    }
    EXPORT_SYMBOL_GPL(pci_dev_unlock);

    --
    2.35.1


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