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    SubjectRe: [PATCH] pci: avoid dead lock between device reset and sriov disable
    [+cc Don, Jason, Leon, just FYI]

    On Mon, Apr 04, 2022 at 02:25:39PM +0800, Jay Zhou wrote:
    > Call trace of PF SRIOV disable:
    > sriov_numvfs_store
    > device_lock <----------------- (1) get the device lock
    > ->sriov_configure # e.g. vfio_pci_sriov_configure
    > sriov_disable
    > pci_cfg_access_lock <--- (4) wait dev->block_cfg_access to be 0
    >
    > Call trace of PF reset:
    > reset_store
    > pci_reset_function
    > pci_dev_lock
    > pci_cfg_access_lock <----- (2) set dev->block_cfg_access = 1
    > device_lock <------------- (3) want to get the device lock
    >
    > These two oprations would wait for each other forever if the
    > code execution sequence is (1)(2)(3)(4).
    >
    > Let's get the device lock and then the config access lock in
    > pci_dev_lock().
    >
    > Signed-off-by: Jay Zhou <jianjay.zhou@huawei.com>

    Thanks, I (finally) applied Yicong's identical patch from a year ago
    to pci/virtualization for v5.19, with a commit log combined and
    adapted from both:

    PCI: Avoid pci_dev_lock() AB/BA deadlock with sriov_numvfs_store()

    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>

    > ---
    > 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 9ecce435fb3f..61a6db1d21f6 100644
    > --- a/drivers/pci/pci.c
    > +++ b/drivers/pci/pci.c
    > @@ -5103,19 +5103,19 @@ static int pci_reset_bus_function(struct pci_dev *dev, bool probe)
    >
    > 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);
    > }
    > EXPORT_SYMBOL_GPL(pci_dev_lock);
    >
    > /* 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;
    > @@ -5124,8 +5124,8 @@ 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);
    >
    > --
    > 2.27.0
    >

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