[dpdk-dev] FW: [SPDK] Re: Potential defect in pci_unplug()

[Niu, Yawei]

On 2020/9/28, 11:44 PM, "Harris, James R" <james.r.harris at intel.com> wrote:

    Hi Niu,
    
    I agree, this doesn't look right.  Could you file an SPDK issue for this to make sure we track it?  And then try sending an e-mail to the DPDK mailing list?  I'm open to submitting a patch to our DPDK submodule short-term, but only if we get agreement with DPDK community that this fix is correct.
    
    Thanks,
    
    Jim
    
    
    On 9/28/20, 12:17 AM, "Niu, Yawei" <yawei.niu at intel.com> wrote:
    
        Hi,
    
        In the pci_unplug() (dpdk/drivers/bus/pci/pci_common.c), why do we call rte_devargs_remove() to remove the saved device args? That looks a defect to me, since that’ll result in the hot removed device failed to be detected when it’s plugged back (when white list option was provided), the situation is described following:
    
          1.  App starts with white list option provided, let’s suppose the device in white list is: 0000:81:00.0;
          2.  rte_devargs_add() is called to add this device arg on rte_eal_init();
          3.  Issue “echo 1 > /sys/bus/pci/devices/0000\:81\:00.0/remove” to hot remove the device;
          4.  pci_unplug() is called to remove the device, and rte_devargs_remove() is called, so this device arg for white list is remove too;
          5.  Issue “echo 1 > /sys/bus/pci/rescan” then “PCI_WHITELIST=”0000:81:00.0” spdk/script/setup.sh” to do hot plug;
          6.  In pci_scan_one(), new dev is generated, however, the dev->device.devargs is set NULL since the device args has been removed on device unplug;
          7.  rte_pci_probe() does white list scan, however, it unexpectedly skips the device because the devargs of the device is NULL now;
    
        I don’t fully understand the DPDK code, but this rte_devargs_remove() in pci_unplug() doesn’t make sense to me (when I commented it out, seems everything will work as expected). Is this a glitch or I missed anything?
    
        Thanks
        -Niu
    
    
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