workqueue: Prevent workqueue versus ata-piix livelock

An Intel i7 system regularly detected rcu_preempt stalls after the kernel
was upgraded from 3.6-rt to 3.8-rt. When the stall happened, disk I/O was no
longer possible, unless the system was restarted.

The kernel message was:
INFO: rcu_preempt self-detected stall on CPU { 6}
[..]
NMI backtrace for cpu 6
CPU 6
Pid: 119, comm: irq/19-ata_piix Not tainted 3.8.13-rt13 #11 Shuttle Inc. SX58/SX58
RIP: 0010:[<ffffffff8124ca60>]  [<ffffffff8124ca60>] ip_compute_csum+0x30/0x30
RSP: 0018:ffff880333303cb0  EFLAGS: 00000002
RAX: 0000000000000006 RBX: 00000000000003e9 RCX: 0000000000000034
RDX: 0000000000000000 RSI: ffffffff81aa16d0 RDI: 0000000000000001
RBP: ffff880333303ce8 R08: ffffffff81aa16d0 R09: ffffffff81c1b8cc
R10: 0000000000000000 R11: 0000000000000000 R12: 000000000005161f
R13: 0000000000000006 R14: ffffffff81aa16d0 R15: 0000000000000002
FS:  0000000000000000(0000) GS:ffff880333300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000003c1b2bb420 CR3: 0000000001a0f000 CR4: 00000000000007e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process irq/19-ata_piix (pid: 119, threadinfo ffff88032d88a000, task ffff88032df80000)
Stack:
ffffffff8124cb32 000000000005161e 00000000000003e9 0000000000001000
0000000000009022 ffffffff81aa16d0 0000000000000002 ffff880333303cf8
ffffffff8124caa9 ffff880333303d08 ffffffff8124cad2 ffff880333303d28
Call Trace:
<IRQ>
[<ffffffff8124cb32>] ? delay_tsc+0x33/0xe3
[<ffffffff8124caa9>] __delay+0xf/0x11
[<ffffffff8124cad2>] __const_udelay+0x27/0x29
[<ffffffff8102d1fa>] native_safe_apic_wait_icr_idle+0x39/0x45
[<ffffffff8102dc9b>] __default_send_IPI_dest_field.constprop.0+0x1e/0x58
[<ffffffff8102dd1e>] default_send_IPI_mask_sequence_phys+0x49/0x7d
[<ffffffff81030326>] physflat_send_IPI_all+0x17/0x19
[<ffffffff8102de53>] arch_trigger_all_cpu_backtrace+0x50/0x79
[<ffffffff810b21d0>] rcu_check_callbacks+0x1cb/0x568
[<ffffffff81048c9c>] ? raise_softirq+0x2e/0x35
[<ffffffff81086be0>] ? tick_sched_do_timer+0x38/0x38
[<ffffffff8104f653>] update_process_times+0x44/0x55
[<ffffffff81086866>] tick_sched_handle+0x4a/0x59
[<ffffffff81086c1c>] tick_sched_timer+0x3c/0x5b
[<ffffffff81062845>] __run_hrtimer+0x9b/0x158
[<ffffffff810631d8>] hrtimer_interrupt+0x172/0x2aa
[<ffffffff8102d498>] smp_apic_timer_interrupt+0x76/0x89
[<ffffffff814d881d>] apic_timer_interrupt+0x6d/0x80
<EOI>
[<ffffffff81057cd2>] ? __local_lock_irqsave+0x17/0x4a
[<ffffffff81059336>] try_to_grab_pending+0x42/0x17e
[<ffffffff8105a699>] mod_delayed_work_on+0x32/0x88
[<ffffffff8105a70b>] mod_delayed_work+0x1c/0x1e
[<ffffffff8122ae84>] blk_run_queue_async+0x37/0x39
[<ffffffff81230985>] flush_end_io+0xf1/0x107
[<ffffffff8122e0da>] blk_finish_request+0x21e/0x264
[<ffffffff8122e162>] blk_end_bidi_request+0x42/0x60
[<ffffffff8122e1ba>] blk_end_request+0x10/0x12
[<ffffffff8132de46>] scsi_io_completion+0x1bf/0x492
[<ffffffff81335cec>] ? sd_done+0x298/0x2ef
[<ffffffff81325a02>] scsi_finish_command+0xe9/0xf2
[<ffffffff8132dbcb>] scsi_softirq_done+0x106/0x10f
[<ffffffff812333d3>] blk_done_softirq+0x77/0x87
[<ffffffff8104826f>] do_current_softirqs+0x172/0x2e1
[<ffffffff810aa820>] ? irq_thread_fn+0x3a/0x3a
[<ffffffff81048466>] local_bh_enable+0x43/0x72
[<ffffffff810aa866>] irq_forced_thread_fn+0x46/0x52
[<ffffffff810ab089>] irq_thread+0x8c/0x17c
[<ffffffff810ab179>] ? irq_thread+0x17c/0x17c
[<ffffffff810aaffd>] ? wake_threads_waitq+0x44/0x44
[<ffffffff8105eb18>] kthread+0x8d/0x95
[<ffffffff8105ea8b>] ? __kthread_parkme+0x65/0x65
[<ffffffff814d7b7c>] ret_from_fork+0x7c/0xb0
[<ffffffff8105ea8b>] ? __kthread_parkme+0x65/0x65

The state of softirqd of this CPU at the time of the crash was:
ksoftirqd/6     R  running task        0    53      2 0x00000000
ffff88032fc39d18 0000000000000046 ffff88033330c4c0 ffff8803303f4710
ffff88032fc39fd8 ffff88032fc39fd8 0000000000000000 0000000000062500
ffff88032df88000 ffff8803303f4710 0000000000000000 ffff88032fc38000
Call Trace:
[<ffffffff8105a3ae>] ? __queue_work+0x27c/0x27c
[<ffffffff814d178c>] preempt_schedule+0x61/0x76
[<ffffffff8106cccf>] migrate_enable+0xe5/0x1df
[<ffffffff8105a3ae>] ? __queue_work+0x27c/0x27c
[<ffffffff8104ef52>] run_timer_softirq+0x161/0x1d6
[<ffffffff8104826f>] do_current_softirqs+0x172/0x2e1
[<ffffffff8104840b>] run_ksoftirqd+0x2d/0x45
[<ffffffff8106658a>] smpboot_thread_fn+0x2ea/0x308
[<ffffffff810662a0>] ? test_ti_thread_flag+0xc/0xc
[<ffffffff810662a0>] ? test_ti_thread_flag+0xc/0xc
[<ffffffff8105eb18>] kthread+0x8d/0x95
[<ffffffff8105ea8b>] ? __kthread_parkme+0x65/0x65
[<ffffffff814d7afc>] ret_from_fork+0x7c/0xb0
[<ffffffff8105ea8b>] ? __kthread_parkme+0x65/0x65

Apparently, the softirq demon and the ata_piix IRQ handler were waiting
for each other to finish ending up in a livelock. After the below patch
was applied, the system no longer crashes.

Reported-by: Carsten Emde <C.Emde@osadl.org>
Proposed-by: Thomas Gleixner <tglx@linutronix.de>
Tested by: Carsten Emde <C.Emde@osadl.org>
Signed-off-by: Carsten Emde <C.Emde@osadl.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

1 files changed, 2 insertions, 1 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 776f6acfc4b6d6..31a2cea908e879 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -49,6 +49,7 @@
 #include <linux/moduleparam.h>
 #include <linux/uaccess.h>
 #include <linux/locallock.h>
+#include <linux/delay.h>
 
 #include "workqueue_internal.h"
 
@@ -1246,7 +1247,7 @@ fail:
 	local_unlock_irqrestore(pendingb_lock, *flags);
 	if (work_is_canceling(work))
 		return -ENOENT;
-	cpu_relax();
+	cpu_chill();
 	return -EAGAIN;
 }