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    Subject[PATCH 3/4] pci aer: fix deadlock in do_recovery
    Date
    CPU0					CPU1
    ---------------------------------------------------------------------
    __driver_attach()
    device_lock(&dev->mutex) <--- device mutex lock here
    driver_probe_device()
    pci_enable_sriov()
    pci_iov_add_virtfn()
    pci_device_add()
    aer_isr() <--- pci aer error
    do_recovery()
    broadcast_error_message()
    pci_walk_bus()
    down_read(&pci_bus_sem) <--- rd sem
    down_write(&pci_bus_sem) <-- stuck on wr sem
    report_error_detected()
    device_lock(&dev->mutex)<--- DEAD LOCK

    This can also happen when aer error occurs while pci_dev->sriov_config() is
    called.

    Only fix I could think of is to lock &pci_bus_sem and try locking all
    device->mutex under that pci_bus. If it fails, unlock all device->mutex
    and &pci_bus_sem and try again.

    [ 70.984091] pcieport 0000:00:02.0: AER: Uncorrected (Non-Fatal) error received: id=0010
    [ 70.984112] pcieport 0000:00:02.0: PCIe Bus Error: severity=Uncorrected (Non-Fatal), type=Transaction Layer, id=0010(Requester ID)
    [ 70.984116] pcieport 0000:00:02.0: device [8086:3c04] error status/mask=00004000/00100000
    [ 70.984120] pcieport 0000:00:02.0: [14] Completion Timeout (First)
    ...
    [ 107.484190] INFO: task kworker/0:1:76 blocked for more than 30 seconds.
    [ 107.563619] Not tainted 4.13.0+ #28
    [ 107.611618] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
    [ 107.705368] kworker/0:1 D 0 76 2 0x80000000
    [ 107.771050] Workqueue: events aer_isr
    [ 107.814895] Call Trace:
    [ 107.844181] __schedule+0x312/0xa40
    [ 107.885928] schedule+0x3d/0x90
    [ 107.923506] schedule_preempt_disabled+0x15/0x20
    [ 107.978773] __mutex_lock+0x304/0xa30
    [ 108.022594] ? dev_printk_emit+0x3b/0x50
    [ 108.069534] ? report_error_detected+0xa6/0x210
    [ 108.123770] mutex_lock_nested+0x1b/0x20
    [ 108.170713] ? mutex_lock_nested+0x1b/0x20
    [ 108.219730] report_error_detected+0xa6/0x210
    [ 108.271881] ? aer_recover_queue+0xe0/0xe0
    [ 108.320904] pci_walk_bus+0x46/0x90
    [ 108.362645] ? aer_recover_queue+0xe0/0xe0
    [ 108.411658] broadcast_error_message+0xc3/0xf0
    [ 108.464835] do_recovery+0x34/0x220
    [ 108.506569] ? get_device_error_info+0x92/0x130
    [ 108.560785] aer_isr+0x28f/0x3b0
    [ 108.599410] process_one_work+0x277/0x6c0
    [ 108.647399] worker_thread+0x4d/0x3b0
    [ 108.691218] kthread+0x171/0x190
    [ 108.729830] ? process_one_work+0x6c0/0x6c0
    [ 108.779888] ? kthread_create_on_node+0x40/0x40
    [ 108.834110] ret_from_fork+0x2a/0x40
    [ 108.876916] INFO: task kworker/0:2:205 blocked for more than 30 seconds.
    [ 108.957129] Not tainted 4.13.0+ #28
    [ 109.005114] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
    [ 109.098873] kworker/0:2 D 0 205 2 0x80000000
    [ 109.164544] Workqueue: events work_for_cpu_fn
    [ 109.216681] Call Trace:
    [ 109.245943] __schedule+0x312/0xa40
    [ 109.287687] ? rwsem_down_write_failed+0x308/0x4f0
    [ 109.345021] schedule+0x3d/0x90
    [ 109.382603] rwsem_down_write_failed+0x30d/0x4f0
    [ 109.437869] ? __lock_acquire+0x75c/0x1410
    [ 109.486910] call_rwsem_down_write_failed+0x17/0x30
    [ 109.545287] ? call_rwsem_down_write_failed+0x17/0x30
    [ 109.605752] down_write+0x88/0xb0
    [ 109.645410] pci_device_add+0x158/0x240
    [ 109.691313] pci_iov_add_virtfn+0x24f/0x340
    [ 109.741375] pci_enable_sriov+0x32b/0x420
    [ 109.789466] ? pci_read+0x2c/0x30
    [ 109.829142] enic_probe+0x5d4/0xff0 [enic]
    [ 109.878184] ? trace_hardirqs_on+0xd/0x10
    [ 109.926180] local_pci_probe+0x42/0xa0
    [ 109.971037] work_for_cpu_fn+0x14/0x20
    [ 110.015898] process_one_work+0x277/0x6c0
    [ 110.063884] worker_thread+0x1d6/0x3b0
    [ 110.108750] kthread+0x171/0x190
    [ 110.147363] ? process_one_work+0x6c0/0x6c0
    [ 110.197426] ? kthread_create_on_node+0x40/0x40
    [ 110.251642] ret_from_fork+0x2a/0x40
    [ 110.294448] INFO: task systemd-udevd:492 blocked for more than 30 seconds.
    [ 110.376742] Not tainted 4.13.0+ #28
    [ 110.424715] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
    [ 110.518457] systemd-udevd D 0 492 444 0x80000180
    [ 110.584116] Call Trace:
    [ 110.613382] __schedule+0x312/0xa40
    [ 110.655127] ? wait_for_completion+0x14a/0x1d0
    [ 110.708302] schedule+0x3d/0x90
    [ 110.745875] schedule_timeout+0x26e/0x5b0
    [ 110.793887] ? wait_for_completion+0x14a/0x1d0
    [ 110.847068] wait_for_completion+0x169/0x1d0
    [ 110.898165] ? wait_for_completion+0x169/0x1d0
    [ 110.951354] ? wake_up_q+0x80/0x80
    [ 110.992060] flush_work+0x237/0x300
    [ 111.033795] ? flush_workqueue_prep_pwqs+0x1b0/0x1b0
    [ 111.093224] ? wait_for_completion+0x5a/0x1d0
    [ 111.145363] ? flush_work+0x237/0x300
    [ 111.189189] work_on_cpu+0x94/0xb0
    [ 111.229894] ? work_is_static_object+0x20/0x20
    [ 111.283070] ? pci_device_shutdown+0x60/0x60
    [ 111.334173] pci_device_probe+0x17a/0x190
    [ 111.382163] driver_probe_device+0x2ff/0x450
    [ 111.433260] __driver_attach+0x103/0x140
    [ 111.480195] ? driver_probe_device+0x450/0x450
    [ 111.533381] bus_for_each_dev+0x74/0xb0
    [ 111.579276] driver_attach+0x1e/0x20
    [ 111.622056] bus_add_driver+0x1ca/0x270
    [ 111.667955] ? 0xffffffffc039c000
    [ 111.707616] driver_register+0x60/0xe0
    [ 111.752472] ? 0xffffffffc039c000
    [ 111.792126] __pci_register_driver+0x6b/0x70
    [ 111.843275] enic_init_module+0x38/0x1000 [enic]
    [ 111.898533] do_one_initcall+0x50/0x192
    [ 111.944428] ? trace_hardirqs_on+0xd/0x10
    [ 111.992408] do_init_module+0x5f/0x1f2
    [ 112.037274] load_module+0x1740/0x1f70
    [ 112.082148] SYSC_finit_module+0xd7/0xf0
    [ 112.129083] ? SYSC_finit_module+0xd7/0xf0
    [ 112.178106] SyS_finit_module+0xe/0x10
    [ 112.222972] do_syscall_64+0x69/0x180
    [ 112.266793] entry_SYSCALL64_slow_path+0x25/0x25
    [ 112.322047] RIP: 0033:0x7f3da098b559
    [ 112.364826] RSP: 002b:00007ffeb3306a38 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
    [ 112.455447] RAX: ffffffffffffffda RBX: 0000557fe41ed3d0 RCX: 00007f3da098b559
    [ 112.540860] RDX: 0000000000000000 RSI: 00007f3da14c79c5 RDI: 0000000000000006
    [ 112.626281] RBP: 00007f3da14c79c5 R08: 0000000000000000 R09: 00007ffeb3306b50
    [ 112.711698] R10: 0000000000000006 R11: 0000000000000246 R12: 0000000000000000
    [ 112.797114] R13: 0000557fe420e210 R14: 0000000000020000 R15: 0000557fe2c1ef4a
    [ 112.882568]
    Showing all locks held in the system:
    [ 112.956545] 5 locks held by kworker/0:1/76:
    [ 113.006616] #0: ("events"){+.+.}, at: [<ffffffffb00b10ed>] process_one_work+0x1ed/0x6c0
    [ 113.104535] #1: ((&rpc->dpc_handler)){+.+.}, at: [<ffffffffb00b10ed>] process_one_work+0x1ed/0x6c0
    [ 113.213894] #2: (&rpc->rpc_mutex){+.+.}, at: [<ffffffffb0505ca2>] aer_isr+0x32/0x3b0
    [ 113.308711] #3: (pci_bus_sem){++++}, at: [<ffffffffb04ea18a>] pci_walk_bus+0x2a/0x90
    [ 113.403501] #4: (&dev->mutex){....}, at: [<ffffffffb0505706>] report_error_detected+0xa6/0x210
    [ 113.508715] 3 locks held by kworker/0:2/205:
    [ 113.559808] #0: ("events"){+.+.}, at: [<ffffffffb00b10ed>] process_one_work+0x1ed/0x6c0
    [ 113.657718] #1: ((&wfc.work)){+.+.}, at: [<ffffffffb00b10ed>] process_one_work+0x1ed/0x6c0
    [ 113.758745] #2: (pci_bus_sem){++++}, at: [<ffffffffb04ec978>] pci_device_add+0x158/0x240
    [ 113.857710] 1 lock held by khungtaskd/239:
    [ 113.906729] #0: (tasklist_lock){.+.+}, at: [<ffffffffb00f07dd>] debug_show_all_locks+0x3d/0x1a0
    [ 114.012972] 2 locks held by systemd-udevd/492:
    [ 114.066148] #0: (&dev->mutex){....}, at: [<ffffffffb06254d5>] __driver_attach+0x55/0x140
    [ 114.165107] #1: (&dev->mutex){....}, at: [<ffffffffb06254f2>] __driver_attach+0x72/0x140

    [ 114.281879] =============================================

    Signed-off-by: Govindarajulu Varadarajan <gvaradar@cisco.com>
    ---
    drivers/pci/pcie/aer/aerdrv_core.c | 50 ++++++++++++++++++++++++++++++--------
    1 file changed, 40 insertions(+), 10 deletions(-)

    diff --git a/drivers/pci/pcie/aer/aerdrv_core.c b/drivers/pci/pcie/aer/aerdrv_core.c
    index 890efcc574cb..a3869a3b6e82 100644
    --- a/drivers/pci/pcie/aer/aerdrv_core.c
    +++ b/drivers/pci/pcie/aer/aerdrv_core.c
    @@ -26,6 +26,7 @@
    #include <linux/slab.h>
    #include <linux/kfifo.h>
    #include "aerdrv.h"
    +#include "../../pci.h"

    #define PCI_EXP_AER_FLAGS (PCI_EXP_DEVCTL_CERE | PCI_EXP_DEVCTL_NFERE | \
    PCI_EXP_DEVCTL_FERE | PCI_EXP_DEVCTL_URRE)
    @@ -241,7 +242,6 @@ static int report_error_detected(struct pci_dev *dev, void *data)
    struct aer_broadcast_data *result_data;
    result_data = (struct aer_broadcast_data *) data;

    - device_lock(&dev->dev);
    dev->error_state = result_data->state;

    if (!dev->driver ||
    @@ -281,7 +281,6 @@ static int report_error_detected(struct pci_dev *dev, void *data)
    }

    result_data->result = merge_result(result_data->result, vote);
    - device_unlock(&dev->dev);
    return 0;
    }

    @@ -292,7 +291,6 @@ static int report_mmio_enabled(struct pci_dev *dev, void *data)
    struct aer_broadcast_data *result_data;
    result_data = (struct aer_broadcast_data *) data;

    - device_lock(&dev->dev);
    if (!dev->driver ||
    !dev->driver->err_handler ||
    !dev->driver->err_handler->mmio_enabled)
    @@ -302,7 +300,6 @@ static int report_mmio_enabled(struct pci_dev *dev, void *data)
    vote = err_handler->mmio_enabled(dev);
    result_data->result = merge_result(result_data->result, vote);
    out:
    - device_unlock(&dev->dev);
    return 0;
    }

    @@ -313,7 +310,6 @@ static int report_slot_reset(struct pci_dev *dev, void *data)
    struct aer_broadcast_data *result_data;
    result_data = (struct aer_broadcast_data *) data;

    - device_lock(&dev->dev);
    if (!dev->driver ||
    !dev->driver->err_handler ||
    !dev->driver->err_handler->slot_reset)
    @@ -323,7 +319,6 @@ static int report_slot_reset(struct pci_dev *dev, void *data)
    vote = err_handler->slot_reset(dev);
    result_data->result = merge_result(result_data->result, vote);
    out:
    - device_unlock(&dev->dev);
    return 0;
    }

    @@ -331,7 +326,6 @@ static int report_resume(struct pci_dev *dev, void *data)
    {
    const struct pci_error_handlers *err_handler;

    - device_lock(&dev->dev);
    dev->error_state = pci_channel_io_normal;

    if (!dev->driver ||
    @@ -342,10 +336,46 @@ static int report_resume(struct pci_dev *dev, void *data)
    err_handler = dev->driver->err_handler;
    err_handler->resume(dev);
    out:
    - device_unlock(&dev->dev);
    return 0;
    }

    +static void aer_pci_walk_bus(struct pci_bus *bus,
    + int (*cb)(struct pci_dev *, void *),
    + struct aer_broadcast_data *res)
    +{
    + bool locked;
    + uint8_t i;
    +
    + for (i = 1; i; i++) {
    + /* PCI driver could hold device->mutex lock and call driver
    + * cb functions which may try to aquire pci_bus_sem.
    + * Trying to aquiring device->mutex lock holding pci_bus_sem
    + * could lead to deadlock.
    + *
    + * Holding pci_bus_sem lets try to aquire device->mutex lock.
    + * If trylock(device->mutex) fails, unlock pci_bus_sem and
    + * try again.
    + */
    + down_read(&pci_bus_sem);
    + locked = __pci_bus_trylock(bus, pci_device_trylock,
    + pci_device_unlock);
    + if (locked)
    + goto out;
    + up_read(&pci_bus_sem);
    + dev_info(&bus->self->dev, "Could not aquire device lock on all subordinates, trying again.");
    + msleep(25);
    + };
    +
    + res->result = PCI_ERS_RESULT_NONE;
    + dev_err(&bus->self->dev, "Could not aquire lock. No aer recovery done.");
    + return;
    +out:
    + /* all devices under this subordinate is locked */
    + __pci_walk_bus(bus, cb, res);
    + __pci_bus_unlock(bus, pci_device_unlock);
    + up_read(&pci_bus_sem);
    +}
    +
    /**
    * broadcast_error_message - handle message broadcast to downstream drivers
    * @dev: pointer to from where in a hierarchy message is broadcasted down
    @@ -380,7 +410,7 @@ static pci_ers_result_t broadcast_error_message(struct pci_dev *dev,
    */
    if (cb == report_error_detected)
    dev->error_state = state;
    - pci_walk_bus(dev->subordinate, cb, &result_data);
    + aer_pci_walk_bus(dev->subordinate, cb, &result_data);
    if (cb == report_resume) {
    pci_cleanup_aer_uncorrect_error_status(dev);
    dev->error_state = pci_channel_io_normal;
    @@ -390,7 +420,7 @@ static pci_ers_result_t broadcast_error_message(struct pci_dev *dev,
    * If the error is reported by an end point, we think this
    * error is related to the upstream link of the end point.
    */
    - pci_walk_bus(dev->bus, cb, &result_data);
    + aer_pci_walk_bus(dev->bus, cb, &result_data);
    }

    return result_data.result;
    --
    2.14.1
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