Hello, I was wondering if any one has a any suggestions to make here. I believe this is a pretty serious deadlock - and I'm looking for ideas on what should be the right way to fix this. Thanks, Rajat On Wed, Mar 11, 2015 at 6:48 PM, Rajat Jain <rajatxjain@xxxxxxxxx> wrote: > Hello, > > > I have hit a kernel deadlock situation on my system that has > hierarchical hot plug situations (i.e. we can hot-plug a card, that > itself may have a hot-plug slot for another level of hot-pluggable > add-on cards). In summary, I see 2 threads that are both waiting on > mutexes that is acquired by the other one. The mutexes are the > (global) "pci_bus_sem" and "device->mutex" respectively. > > > Thread1 > ======= > This is the pciehp worker thread, that scans a new card, and on > finding that there is a hotplug slot downstream, tries to > pci_create_slot(). > pciehp_power_thread() > -> pciehp_enable_slot() > -> pciehp_configure_device() > -> pci_bus_add_devices() discovers all devices including a new > hotplug slot. > -> ....(etc)... > -> device_attach(dev) (for the newly discovered HP slot / > downstream port) > -> device_lock(dev) SUCCESSFULLY ACQUIRES dev->mutex for > the new slot. > -> ....(etc)... > -> ... (goes on) > -> pciehp_probe(dev) > -> __pci_hp_register() > -> pci_create_slot() > -> down_write(pci_bus_sem); /* Deadlocked */ > > This how the stack looks like: > [<ffffffff814e9923>] call_rwsem_down_write_failed+0x13/0x20 > [<ffffffff81522d4f>] pci_create_slot+0x3f/0x280 > [<ffffffff8152c030>] __pci_hp_register+0x70/0x400 > [<ffffffff8152cf49>] pciehp_probe+0x1a9/0x450 > [<ffffffff8152865d>] pcie_port_probe_service+0x3d/0x90 > [<ffffffff815c45b9>] driver_probe_device+0xf9/0x350 > [<ffffffff815c490b>] __device_attach+0x4b/0x60 > [<ffffffff815c25a6>] bus_for_each_drv+0x56/0xa0 > [<ffffffff815c4468>] device_attach+0xa8/0xc0 > [<ffffffff815c38d0>] bus_probe_device+0xb0/0xe0 > [<ffffffff815c16ce>] device_add+0x3de/0x560 > [<ffffffff815c1a2e>] device_register+0x1e/0x30 > [<ffffffff81528aef>] pcie_port_device_register+0x32f/0x510 > [<ffffffff81528eb8>] pcie_portdrv_probe+0x48/0x80 > [<ffffffff8151b17c>] pci_device_probe+0x9c/0xf0 > [<ffffffff815c45b9>] driver_probe_device+0xf9/0x350 > [<ffffffff815c490b>] __device_attach+0x4b/0x60 > [<ffffffff815c25a6>] bus_for_each_drv+0x56/0xa0 > [<ffffffff815c4468>] device_attach+0xa8/0xc0 > [<ffffffff815116c1>] pci_bus_add_device+0x41/0x70 > [<ffffffff81511a41>] pci_bus_add_devices+0x41/0x90 > [<ffffffff81511a6f>] pci_bus_add_devices+0x6f/0x90 > [<ffffffff8152e7e2>] pciehp_configure_device+0xa2/0x140 > [<ffffffff8152df08>] pciehp_enable_slot+0x188/0x2d0 > [<ffffffff8152e3d1>] pciehp_power_thread+0x2b1/0x3c0 > [<ffffffff810d92a0>] process_one_work+0x1d0/0x510 > [<ffffffff810d9cc1>] worker_thread+0x121/0x440 > [<ffffffff810df0bf>] kthread+0xef/0x110 > [<ffffffff81a4d8ac>] ret_from_fork+0x7c/0xb0 > [<ffffffffffffffff>] 0xffffffffffffffff > > > Thread2 > ======= > While the above thread is doing its work, the root port gets a > completion timeout. And thus the AER Error recovery worker thread > kicks in to handle that error. And as part of that error recovery - > since the completion timeout was detected at root port, attempts to > see for ALL the devices downstream if they have an error handler that > need to be called. Here is what happens: > > > aer_isr() > -> aer_isr_one_error() > -> aer_process_err_device() > -> ... (etc)... > -> do_recovery() > -> broadcast_error_message() > -> pci_walk_bus( ..., report_error_detected,...) /* > effectively for all buses below root port */ > -> down_read(&pci_bus_sem); /* SUCCESSFULLY > ACQUIRES the semaophore */ > -> report_error_detected(dev) /* for the newly > detected slot */ > -> device_lock(dev) /* Deadlocked */ > > This is how the stack looks like: > [<ffffffff81529e7e>] report_error_detected+0x4e/0x170 <--- Waiting on > device_lock() > [<ffffffff8151162e>] pci_walk_bus+0x4e/0xa0 > [<ffffffff81529b84>] broadcast_error_message+0xc4/0xf0 > [<ffffffff81529bed>] do_recovery+0x3d/0x280 > [<ffffffff8152a5d0>] aer_isr+0x300/0x3e0 > [<ffffffff810d92a0>] process_one_work+0x1d0/0x510 > [<ffffffff810d9cc1>] worker_thread+0x121/0x440 > [<ffffffff810df0bf>] kthread+0xef/0x110 > [<ffffffff81a4d8ac>] ret_from_fork+0x7c/0xb0 > [<ffffffffffffffff>] 0xffffffffffffffff > > > As a temporary work around to let me proceed, I was thinking may be I > could change in report_error_detected() such that completion timeouts > errors may not be broadcast (do we really have any drivers that have > aer handlers that handle such an error? What would the handler do > anyway to fix such an error?) > > > But not sure what the right solution might look like. I thought about > whether these locks should have been taken in a particular order in > order to avoid this problem, but looking at the stack there seems to > be no other way. What do you think is the best way to fix this > deadlock? > > Any help or suggestions in this regard are greatly appreciated. > > Thanks, > > Rajat -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
