Hi Thomas,
I'm seeing the lockdep barf below on some bare metal Power8 machines.
This seems to be caused by our smp_cpus_done(), which does:
void __init smp_cpus_done(unsigned int max_cpus)
{
/*
* We want the setup_cpu() here to be called on the boot CPU, but
* init might run on any CPU, so make sure it's invoked on the boot
* CPU.
*/
if (smp_ops && smp_ops->setup_cpu)
work_on_cpu_safe(boot_cpuid, smp_setup_cpu_workfn, NULL);
I don't think CPU hotplug can happen at this point, so I don't think
there's really a bug.
But it looks like the work_on_cpu_safe() call could just go away, since
you pinned init to the boot CPU in 8fb12156b8db ("init: Pin init task to
the boot CPU, initially"). Though I can't see where init is unpinned, so
maybe we do still need to do it?
cheers
[ 1.468911] ipr: IBM Power RAID SCSI Device Driver version: 2.6.4 (March 14,
2017)
[ 1.469032] ipr 0001:08:00.0: Found IOA with IRQ: 0
[ 1.469167]
[ 1.469193] ======================================================
[ 1.469250] WARNING: possible circular locking dependency detected
[ 1.469309] 4.12.0-gcc6-gb40b238 #1 Not tainted
[ 1.469355] ------------------------------------------------------
[ 1.469413] kworker/0:1/971 is trying to acquire lock:
[ 1.469459] (cpu_hotplug_lock.rw_sem){++++++}, at: [<c000000000100974>]
apply_workqueue_attrs+0x34/0xa0
[ 1.469544]
[ 1.469544] but task is already holding lock:
[ 1.469602] ((&wfc.work)){+.+.+.}, at: [<c0000000000fdb2c>]
process_one_work+0x25c/0x800
[ 1.469674]
[ 1.469674] which lock already depends on the new lock.
[ 1.469674]
[ 1.469744]
[ 1.469744] the existing dependency chain (in reverse order) is:
[ 1.469813]
[ 1.469813] -> #1 ((&wfc.work)){+.+.+.}:
[ 1.469862] flush_work+0x74/0x340
[ 1.469898] work_on_cpu+0xb8/0xe0
[ 1.469934] work_on_cpu_safe+0x80/0xd0
[ 1.469982] smp_cpus_done+0x54/0xb0
[ 1.470017] smp_init+0x1a0/0x1cc
[ 1.470053] kernel_init_freeable+0x1f4/0x3b0
[ 1.470100] kernel_init+0x24/0x160
[ 1.470137] ret_from_kernel_thread+0x5c/0x74
[ 1.470183]
[ 1.470183] -> #0 (cpu_hotplug_lock.rw_sem){++++++}:
[ 1.470244] lock_acquire+0xec/0x2e0
[ 1.470279] cpus_read_lock+0x4c/0xd0
[ 1.470315] apply_workqueue_attrs+0x34/0xa0
[ 1.470362] __alloc_workqueue_key+0x1b4/0x5b4
[ 1.470410] scsi_host_alloc+0x328/0x4b0
[ 1.470457] ipr_probe+0xb4/0x1f00
[ 1.470493] local_pci_probe+0x6c/0x140
[ 1.470541] work_for_cpu_fn+0x38/0x60
[ 1.470588] process_one_work+0x310/0x800
[ 1.470635] worker_thread+0x2b0/0x520
[ 1.470682] kthread+0x164/0x1b0
[ 1.470718] ret_from_kernel_thread+0x5c/0x74
[ 1.470764]
[ 1.470764] other info that might help us debug this:
[ 1.470764]
[ 1.470834] Possible unsafe locking scenario:
[ 1.470834]
[ 1.470891] CPU0 CPU1
[ 1.470937] ---- ----
[ 1.470984] lock((&wfc.work));
[ 1.471020] lock(cpu_hotplug_lock.rw_sem);
[ 1.471078] lock((&wfc.work));
[ 1.471136] lock(cpu_hotplug_lock.rw_sem);
[ 1.471183]
[ 1.471183] *** DEADLOCK ***
[ 1.471183]
[ 1.471242] 2 locks held by kworker/0:1/971:
[ 1.471289] #0: ("events"){.+.+.+}, at: [<c0000000000fdb2c>]
process_one_work+0x25c/0x800
[ 1.471360] #1: ((&wfc.work)){+.+.+.}, at: [<c0000000000fdb2c>]
process_one_work+0x25c/0x800
[ 1.471488]
[ 1.471488] stack backtrace:
[ 1.471582] CPU: 0 PID: 971 Comm: kworker/0:1 Not tainted
4.12.0-gcc6-gb40b238 #1
[ 1.471721] Workqueue: events work_for_cpu_fn
[ 1.471813] Call Trace:
[ 1.471859] [c0000007f877f560] [c000000000b491b8] dump_stack+0xe8/0x160
(unreliable)
[ 1.471996] [c0000007f877f5a0] [c000000000153e68]
print_circular_bug+0x288/0x3d0
[ 1.472133] [c0000007f877f640] [c000000000157ec8]
__lock_acquire+0x1858/0x1a20
[ 1.472271] [c0000007f877f7b0] [c000000000158bfc] lock_acquire+0xec/0x2e0
[ 1.472386] [c0000007f877f880] [c0000000000d4f8c] cpus_read_lock+0x4c/0xd0
[ 1.472501] [c0000007f877f8b0] [c000000000100974]
apply_workqueue_attrs+0x34/0xa0
[ 1.472639] [c0000007f877f8f0] [c000000000102ef4]
__alloc_workqueue_key+0x1b4/0x5b4
[ 1.472776] [c0000007f877f9b0] [c00000000078cd58] scsi_host_alloc+0x328/0x4b0
[ 1.472913] [c0000007f877fa50] [c0000000007bd414] ipr_probe+0xb4/0x1f00
[ 1.473028] [c0000007f877fbb0] [c0000000006157fc] local_pci_probe+0x6c/0x140
[ 1.473166] [c0000007f877fc40] [c0000000000f8298] work_for_cpu_fn+0x38/0x60
[ 1.473281] [c0000007f877fc70] [c0000000000fdbe0]
process_one_work+0x310/0x800
[ 1.473418] [c0000007f877fd30] [c0000000000fe380] worker_thread+0x2b0/0x520
[ 1.473534] [c0000007f877fdc0] [c000000000107c84] kthread+0x164/0x1b0
[ 1.473649] [c0000007f877fe30] [c00000000000b6e8]
ret_from_kernel_thread+0x5c/0x74
