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SubjectRe: hotplug lockdep splat (tip)
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On Mon, 2017-09-04 at 09:55 +0200, Peter Zijlstra wrote:
> On Sun, Sep 03, 2017 at 08:59:35AM +0200, Mike Galbraith wrote:
> >
> > [ 126.626908] Unregister pv shared memory for cpu 1
> > [ 126.631041]
> > [ 126.631269] ======================================================
> > [ 126.632442] WARNING: possible circular locking dependency detected
> > [ 126.633599] 4.13.0.g06260ca-tip-lockdep #2 Tainted: G E
> > [ 126.634380] ------------------------------------------------------
> > [ 126.635124] stress-cpu-hotp/3156 is trying to acquire lock:
> > [ 126.635804] ((complete)&st->done){+.+.}, at: [<ffffffff8108d19a>] takedown_cpu+0x8a/0xf0
> > [ 126.636809]
> > [ 126.636809] but task is already holding lock:
> > [ 126.637567] (sparse_irq_lock){+.+.}, at: [<ffffffff81107ac7>] irq_lock_sparse+0x17/0x20
> > [ 126.638665]
>
> https://lkml.kernel.org/r/20170829193416.GC32112@worktop.programming.kicks-ass.net

Well, flavor of gripe changed.

[ 164.114290] ======================================================
[ 164.115146] WARNING: possible circular locking dependency detected
[ 164.115751] 4.13.0.g90abd70-tip-lockdep #4 Tainted: G E
[ 164.116348] ------------------------------------------------------
[ 164.116919] cpuhp/0/12 is trying to acquire lock:
[ 164.117381] (cpuhp_state){+.+.}, at: [<ffffffff8108e4aa>] cpuhp_thread_fun+0x2a/0x160
[ 164.118097]
but now in release context of a crosslock acquired at the following:
[ 164.118845] ((complete)&per_cpu_ptr(&cpuhp_state, i)->done#2){+.+.}, at: [<ffffffff8108e71f>] cpuhp_issue_call+0x13f/0x170
[ 164.119789]
which lock already depends on the new lock.

[ 164.120483]
the existing dependency chain (in reverse order) is:
[ 164.121121]
-> #2 ((complete)&per_cpu_ptr(&cpuhp_state, i)->done#2){+.+.}:
[ 164.121840] __lock_acquire+0x116a/0x11c0
[ 164.122382] lock_acquire+0xbd/0x200
[ 164.122741] wait_for_completion+0x53/0x1a0
[ 164.123181] takedown_cpu+0x8a/0xf0
[ 164.123533] cpuhp_invoke_callback+0x1f6/0x830
[ 164.123967] cpuhp_down_callbacks+0x42/0x80
[ 164.124433] _cpu_down+0x155/0x190
[ 164.124779] do_cpu_down+0x3e/0x60
[ 164.125127] cpu_down+0x10/0x20
[ 164.125456] cpu_subsys_offline+0x14/0x20
[ 164.125937] device_offline+0x8c/0xb0
[ 164.126487] online_store+0x40/0x80
[ 164.126943] dev_attr_store+0x18/0x30
[ 164.127335] sysfs_kf_write+0x44/0x60
[ 164.127703] kernfs_fop_write+0x113/0x1a0
[ 164.128141] __vfs_write+0x28/0x150
[ 164.128532] vfs_write+0xc7/0x1c0
[ 164.128871] SyS_write+0x49/0xa0
[ 164.129206] entry_SYSCALL_64_fastpath+0x1f/0xbe
[ 164.129656]
-> #1 (sparse_irq_lock){+.+.}:
[ 164.130145] __lock_acquire+0x116a/0x11c0
[ 164.130546] lock_acquire+0xbd/0x200
[ 164.130913] __mutex_lock+0x70/0x8e0
[ 164.131276] mutex_lock_nested+0x1b/0x20
[ 164.131664] irq_lock_sparse+0x17/0x20
[ 164.132039] irq_affinity_online_cpu+0x18/0xd0
[ 164.132463] cpuhp_invoke_callback+0x1f6/0x830
[ 164.132928] cpuhp_up_callbacks+0x37/0xb0
[ 164.133487] cpuhp_thread_fun+0x14f/0x160
[ 164.133885] smpboot_thread_fn+0x11a/0x1e0
[ 164.134333] kthread+0x152/0x190
[ 164.134652] ret_from_fork+0x2a/0x40
[ 164.135010]
-> #0 (cpuhp_state){+.+.}:
[ 164.135454] cpuhp_thread_fun+0x54/0x160
[ 164.135834] smpboot_thread_fn+0x11a/0x1e0
[ 164.136235] kthread+0x152/0x190
[ 164.136558] ret_from_fork+0x2a/0x40
[ 164.136920] 0xffffffffffffffff
[ 164.137239]
other info that might help us debug this:

[ 164.137927] Chain exists of:
cpuhp_state --> sparse_irq_lock --> (complete)&per_cpu_ptr(&cpuhp_state, i)->done#2

[ 164.139136] Possible unsafe locking scenario by crosslock:

[ 164.139898] CPU0 CPU1
[ 164.140298] ---- ----
[ 164.140689] lock(sparse_irq_lock);
[ 164.141015] lock((complete)&per_cpu_ptr(&cpuhp_state, i)->done#2);
[ 164.141565] lock(cpuhp_state);
[ 164.142077] unlock((complete)&per_cpu_ptr(&cpuhp_state, i)->done#2);
[ 164.142859]
*** DEADLOCK ***

[ 164.143382] 1 lock held by cpuhp/0/12:
[ 164.143794] #0: (&x->wait#2){-...}, at: [<ffffffff810e1afd>] complete+0x1d/0x60
[ 164.144461]
stack backtrace:
[ 164.144837] CPU: 0 PID: 12 Comm: cpuhp/0 Tainted: G E 4.13.0.g90abd70-tip-lockdep #4
[ 164.145594] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.0.0-prebuilt.qemu-project.org 04/01/2014
[ 164.146485] Call Trace:
[ 164.146707] dump_stack+0x85/0xc5
[ 164.147004] print_circular_bug+0x2e9/0x2f7
[ 164.147369] check_prev_add+0x666/0x700
[ 164.147706] ? print_bfs_bug+0x40/0x40
[ 164.148045] ? trace_hardirqs_on+0xd/0x10
[ 164.148389] lock_commit_crosslock+0x410/0x5a0
[ 164.148780] complete+0x29/0x60
[ 164.149064] cpuhp_thread_fun+0xa1/0x160
[ 164.149433] ? cpuhp_thread_fun+0x2a/0x160
[ 164.149814] smpboot_thread_fn+0x11a/0x1e0
[ 164.150193] kthread+0x152/0x190
[ 164.150482] ? sort_range+0x30/0x30
[ 164.150781] ? kthread_create_on_node+0x40/0x40
[ 164.151184] ret_from_fork+0x2a/0x40

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