• Dexuan Cui's avatar
    Drivers: hv: vmbus: Offload the handling of channels to two workqueues · 37c2578c
    Dexuan Cui authored
    vmbus_process_offer() mustn't call channel->sc_creation_callback()
    directly for sub-channels, because sc_creation_callback() ->
    vmbus_open() may never get the host's response to the
    OPEN_CHANNEL message (the host may rescind a channel at any time,
    e.g. in the case of hot removing a NIC), and vmbus_onoffer_rescind()
    may not wake up the vmbus_open() as it's blocked due to a non-zero
    vmbus_connection.offer_in_progress, and finally we have a deadlock.
    
    The above is also true for primary channels, if the related device
    drivers use sync probing mode by default.
    
    And, usually the handling of primary channels and sub-channels can
    depend on each other, so we should offload them to different
    workqueues to avoid possible deadlock, e.g. in sync-probing mode,
    NIC1's netvsc_subchan_work() can race with NIC2's netvsc_probe() ->
    rtnl_lock(), and causes deadlock: the former gets the rtnl_lock
    and waits for all the sub-channels to appear, but the latter
    can't get the rtnl_lock and this blocks the handling of sub-channels.
    
    The patch can fix the multiple-NIC deadlock described above for
    v3.x kernels (e.g. RHEL 7.x) which don't support async-probing
    of devices, and v4.4, v4.9, v4.14 and v4.18 which support async-probing
    but don't enable async-probing for Hyper-V drivers (yet).
    
    The patch can also fix the hang issue in sub-channel's handling described
    above for all versions of kernels, including v4.19 and v4.20-rc4.
    
    So actually the patch should be applied to all the existing kernels,
    not only the kernels that have 8195b139.
    
    Fixes: 8195b139 ("hv_netvsc: fix deadlock on hotplug")
    Cc: stable@vger.kernel.org
    Cc: Stephen Hemminger <sthemmin@microsoft.com>
    Cc: K. Y. Srinivasan <kys@microsoft.com>
    Cc: Haiyang Zhang <haiyangz@microsoft.com>
    Signed-off-by: default avatarDexuan Cui <decui@microsoft.com>
    Signed-off-by: default avatarK. Y. Srinivasan <kys@microsoft.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    37c2578c
channel_mgmt.c 36 KB