The following lockdep report triggers since 3.9-rc1:
=============================================
[ INFO: possible recursive locking detected ]
3.9.0-rc1 #96 Not tainted
---------------------------------------------
kworker/0:1/734 is trying to acquire lock:
((&wfc.work)){+.+.+.}, at: [<ffffffff81066cb0>] flush_work+0x0/0x250
but task is already holding lock:
((&wfc.work)){+.+.+.}, at: [<ffffffff81064352>]
process_one_work+0x162/0x4c0
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock((&wfc.work));
lock((&wfc.work));
*** DEADLOCK ***
May be due to missing lock nesting notation
3 locks held by kworker/0:1/734:
#0: (events){.+.+.+}, at: [<ffffffff81064352>]
process_one_work+0x162/0x4c0
#1: ((&wfc.work)){+.+.+.}, at: [<ffffffff81064352>]
process_one_work+0x162/0x4c0
#2: (&__lockdep_no_validate__){......}, at: [<ffffffff812db225>]
device_attach+0x25/0xb0
stack backtrace:
Pid: 734, comm: kworker/0:1 Not tainted 3.9.0-rc1 #96
Call Trace:
[<ffffffff810948ec>] validate_chain+0xdcc/0x11f0
[<ffffffff81095150>] __lock_acquire+0x440/0xc70
[<ffffffff81095150>] ? __lock_acquire+0x440/0xc70
[<ffffffff810959da>] lock_acquire+0x5a/0x70
[<ffffffff81066cb0>] ? wq_worker_waking_up+0x60/0x60
[<ffffffff81066cf5>] flush_work+0x45/0x250
[<ffffffff81066cb0>] ? wq_worker_waking_up+0x60/0x60
[<ffffffff810922be>] ? mark_held_locks+0x9e/0x130
[<ffffffff81066a96>] ? queue_work_on+0x46/0x90
[<ffffffff810925dd>] ? trace_hardirqs_on_caller+0xfd/0x190
[<ffffffff8109267d>] ? trace_hardirqs_on+0xd/0x10
[<ffffffff81066f74>] work_on_cpu+0x74/0x90
[<ffffffff81063820>] ? keventd_up+0x20/0x20
[<ffffffff8121fd30>] ? pci_pm_prepare+0x60/0x60
[<ffffffff811f9293>] ? cpumask_next_and+0x23/0x40
[<ffffffff81220a1a>] pci_device_probe+0xba/0x110
[<ffffffff812dadca>] ? driver_sysfs_add+0x7a/0xb0
[<ffffffff812daf1f>] driver_probe_device+0x8f/0x230
[<ffffffff812db170>] ? __driver_attach+0xb0/0xb0
[<ffffffff812db1bb>] __device_attach+0x4b/0x60
[<ffffffff812d9314>] bus_for_each_drv+0x64/0x90
[<ffffffff812db298>] device_attach+0x98/0xb0
[<ffffffff81218474>] pci_bus_add_device+0x24/0x50
[<ffffffff81232e80>] virtfn_add+0x240/0x3e0
[<ffffffff8146ce3d>] ? _raw_spin_unlock_irqrestore+0x3d/0x80
[<ffffffff812333be>] pci_enable_sriov+0x23e/0x500
[<ffffffffa011fa1a>] __mlx4_init_one+0x5da/0xce0 [mlx4_core]
[<ffffffffa012016d>] mlx4_init_one+0x2d/0x60 [mlx4_core]
[<ffffffff8121fd79>] local_pci_probe+0x49/0x80
[<ffffffff81063833>] work_for_cpu_fn+0x13/0x20
[<ffffffff810643b8>] process_one_work+0x1c8/0x4c0
[<ffffffff81064352>] ? process_one_work+0x162/0x4c0
[<ffffffff81064cfb>] worker_thread+0x30b/0x430
[<ffffffff810649f0>] ? manage_workers+0x340/0x340
[<ffffffff8106cea6>] kthread+0xd6/0xe0
[<ffffffff8106cdd0>] ? __init_kthread_worker+0x70/0x70
[<ffffffff8146daac>] ret_from_fork+0x7c/0xb0
[<ffffffff8106cdd0>] ? __init_kthread_worker+0x70/0x70
The issue is that a driver, in it's probe function, calls
pci_sriov_enable so a PF device probe causes VF probe (AKA nested
probe). Each probe in pci_device_probe which is (normally) run through
work_on_cpu (this is to get the right numa node for memory allocated by
the driver). In turn work_on_cpu does this internally:
schedule_work_on(cpu, &wfc.work);
flush_work(&wfc.work);
So if you are running probe on CPU1, and cause another
probe on the same CPU, this will try to flush
workqueue from inside same workqueue which causes
a lockep warning.
Nested probing might be tricky to get right generally.
But for pci_sriov_enable, the situation is actually very simple: all VFs
naturally have same affinity as the PF, and cpumask_any_and is actually
same as cpumask_first_and, so it always gives us the same CPU.
So let's just detect that, and run the probing for VFs locally without a
workqueue.
This is hardly elegant, but looks to me like an appropriate quick fix
for 3.9.
Tested-by: Or Gerlitz <ogerlitz@xxxxxxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
---
Changes from v1:
- clarified commit log and added Ack by Tejun Heo
patch is unchanged.
diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index 1fa1e48..6eeb5ec 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -286,8 +286,8 @@ static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev,
int cpu;
get_online_cpus();
cpu = cpumask_any_and(cpumask_of_node(node), cpu_online_mask);
- if (cpu < nr_cpu_ids)
+ if (cpu != raw_smp_processor_id() && cpu < nr_cpu_ids)
error = work_on_cpu(cpu, local_pci_probe, &ddi);
else
error = local_pci_probe(&ddi);
--
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