Oops.
While doing further tests on my patch I found a problem:
[ 82.390739] =================================
[ 82.390749] [ INFO: inconsistent lock state ]
[ 82.390759] 4.7.0-rc2+ #5 Not tainted
[ 82.390768] ---------------------------------
[ 82.390777] inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
[ 82.390790] swapper/5/0 [HC1[1]:SC0[0]:HE0:SE1] takes:
[ 82.390801] (css_set_lock){?.+...}, at: [<ffffffff8115e1cc>] put_css_set+0x4c/0x70
[ 82.390854] {HARDIRQ-ON-W} state was registered at:
[ 82.390865] [<ffffffff8110a4ef>] mark_held_locks+0x6f/0xa0
[ 82.390880] [<ffffffff8110a5c5>] trace_hardirqs_on_caller+0xa5/0x1b0
[ 82.390896] [<ffffffff8110a6dd>] trace_hardirqs_on+0xd/0x10
[ 82.390910] [<ffffffff8188c59c>] _raw_spin_unlock_irq+0x2c/0x40
[ 82.390926] [<ffffffff8116361c>] cgroup_mount+0x59c/0xc10
[ 82.390941] [<ffffffff812871a8>] mount_fs+0x38/0x170
[ 82.390956] [<ffffffff812a866b>] vfs_kern_mount+0x6b/0x150
[ 82.390979] [<ffffffff812ab3a0>] do_mount+0x250/0xe80
[ 82.391012] [<ffffffff812ac305>] SyS_mount+0x95/0xe0
[ 82.391044] [<ffffffff8188cc7c>] entry_SYSCALL_64_fastpath+0x1f/0xbd
[ 82.391071] irq event stamp: 92782
[ 82.391084] hardirqs last enabled at (92779): [<ffffffff8103e69e>] default_idle+0x1e/0x160
[ 82.391116] hardirqs last disabled at (92780): [<ffffffff8188d9a1>] apic_timer_interrupt+0x91/0xa0
[ 82.391152] softirqs last enabled at (92782): [<ffffffff810b64d1>] _local_bh_enable+0x21/0x50
[ 82.391184] softirqs last disabled at (92781): [<ffffffff810b750c>] irq_enter+0x6c/0x90
[ 82.391202]
other info that might help us debug this:
[ 82.391215] Possible unsafe locking scenario:
[ 82.391228] CPU0
[ 82.391233] ----
[ 82.391239] lock(css_set_lock);
[ 82.391249] <Interrupt>
[ 82.391255] lock(css_set_lock);
[ 82.391265]
*** DEADLOCK ***
q
[ 82.391460] no locks held by swapper/5/0.
[ 82.391621]
stack backtrace:
[ 82.391910] CPU: 5 PID: 0 Comm: swapper/5 Not tainted 4.7.0-rc2+ #5
[ 82.392045] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.8.2-20150714_191134- 04/01/2014
[ 82.392180] 0000000000000086 8f22cb6bc668205e ffff88013fd43c20 ffffffff81438973
[ 82.392315] ffff88013a45a680 ffffffff82857680 ffff88013fd43c70 ffffffff81109e45
[ 82.392448] 0000000000000000 0000000000000000 ffff880100000001 0000000000000002
[ 82.392578] Call Trace:
[ 82.392691] <IRQ> [<ffffffff81438973>] dump_stack+0x85/0xc2
[ 82.392817] [<ffffffff81109e45>] print_usage_bug+0x215/0x240
[ 82.392939] [<ffffffff8110a3c0>] mark_lock+0x550/0x610
[ 82.393052] [<ffffffff811093a0>] ? check_usage_backwards+0x160/0x160
[ 82.393167] [<ffffffff8110b10e>] __lock_acquire+0x6ee/0x1440
[ 82.393281] [<ffffffff8112787d>] ? debug_lockdep_rcu_enabled+0x1d/0x20
[ 82.393396] [<ffffffff8110b1ee>] ? __lock_acquire+0x7ce/0x1440
[ 82.393509] [<ffffffff8110b228>] ? __lock_acquire+0x808/0x1440
[ 82.393621] [<ffffffff8110c2d0>] lock_acquire+0xf0/0x1d0
[ 82.393731] [<ffffffff8115e1cc>] ? put_css_set+0x4c/0x70
[ 82.393850] [<ffffffff8188cbc9>] _raw_spin_lock_irqsave+0x49/0x5d
[ 82.393985] [<ffffffff8115e1cc>] ? put_css_set+0x4c/0x70
[ 82.394093] [<ffffffff8115e1cc>] put_css_set+0x4c/0x70
[ 82.394201] [<ffffffff81165591>] cgroup_free+0x91/0x120
[ 82.394310] [<ffffffff810ad0d2>] __put_task_struct+0x42/0x140
[ 82.394419] [<ffffffff810fd064>] dl_task_timer+0xc4/0x2c0
[ 82.394528] [<ffffffff810fcfa0>] ? enqueue_task_dl+0x480/0x480
[ 82.394638] [<ffffffff811349cb>] __hrtimer_run_queues+0xfb/0x4c0
[ 82.394749] [<ffffffff8113556b>] hrtimer_interrupt+0xab/0x1b0
[ 82.394864] [<ffffffff81059798>] local_apic_timer_interrupt+0x38/0x60
[ 82.394976] [<ffffffff8188f91d>] smp_apic_timer_interrupt+0x3d/0x50
[ 82.395087] [<ffffffff8188d9a6>] apic_timer_interrupt+0x96/0xa0
[ 82.395196] <EOI> [<ffffffff8106b806>] ? native_safe_halt+0x6/0x10
[ 82.395310] [<ffffffff8110a6dd>] ? trace_hardirqs_on+0xd/0x10
[ 82.395420] [<ffffffff8103e6a3>] default_idle+0x23/0x160
[ 82.395528] [<ffffffff8103ef6f>] arch_cpu_idle+0xf/0x20
[ 82.395637] [<ffffffff810fecaa>] default_idle_call+0x2a/0x40
[ 82.395744] [<ffffffff810fefea>] cpu_startup_entry+0x32a/0x400
[ 82.395854] [<ffffffff81057f5a>] start_secondary+0x15a/0x190
This problem is fixed with this change:
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index c695d55..fcc8aee 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1928,8 +1928,12 @@ static void cgroup_enable_task_cg_lists(void)
* entry won't be deleted though the process has exited.
* Do it while holding siglock so that we don't end up
* racing against cgroup_exit().
+ *
+ * Interruptions were already disabled when acquiring
+ * the css_set_lock, so we do not need to disable it
+ * again when acquiring the sighand->siglock here.
*/
- spin_lock_irq(&p->sighand->siglock);
+ spin_lock(&p->sighand->siglock);
if (!(p->flags & PF_EXITING)) {
struct css_set *cset = task_css_set(p);
@@ -1938,7 +1942,7 @@ static void cgroup_enable_task_cg_lists(void)
list_add_tail(&p->cg_list, &cset->tasks);
get_css_set(cset);
}
- spin_unlock_irq(&p->sighand->siglock);
+ spin_unlock(&p->sighand->siglock);
} while_each_thread(g, p);
read_unlock(&tasklist_lock);
out_unlock:
I will prepare a v2 of the patch including this change.
I am sorry for the noise.
-- Daniel
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