This is a note to let you know that I've just added the patch titled
timekeeping: Use deferred printk() in debug code
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
timekeeping-use-deferred-printk-in-debug-code.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From f222449c9dfad7c9bb8cb53e64c5c407b172ebbc Mon Sep 17 00:00:00 2001
From: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx>
Date: Wed, 15 Feb 2017 13:43:32 +0900
Subject: timekeeping: Use deferred printk() in debug code
From: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx>
commit f222449c9dfad7c9bb8cb53e64c5c407b172ebbc upstream.
We cannot do printk() from tk_debug_account_sleep_time(), because
tk_debug_account_sleep_time() is called under tk_core seq lock.
The reason why printk() is unsafe there is that console_sem may
invoke scheduler (up()->wake_up_process()->activate_task()), which,
in turn, can return back to timekeeping code, for instance, via
get_time()->ktime_get(), deadlocking the system on tk_core seq lock.
[ 48.950592] ======================================================
[ 48.950622] [ INFO: possible circular locking dependency detected ]
[ 48.950622] 4.10.0-rc7-next-20170213+ #101 Not tainted
[ 48.950622] -------------------------------------------------------
[ 48.950622] kworker/0:0/3 is trying to acquire lock:
[ 48.950653] (tk_core){----..}, at: [<c01cc624>] retrigger_next_event+0x4c/0x90
[ 48.950683]
but task is already holding lock:
[ 48.950683] (hrtimer_bases.lock){-.-...}, at: [<c01cc610>] retrigger_next_event+0x38/0x90
[ 48.950714]
which lock already depends on the new lock.
[ 48.950714]
the existing dependency chain (in reverse order) is:
[ 48.950714]
-> #5 (hrtimer_bases.lock){-.-...}:
[ 48.950744] _raw_spin_lock_irqsave+0x50/0x64
[ 48.950775] lock_hrtimer_base+0x28/0x58
[ 48.950775] hrtimer_start_range_ns+0x20/0x5c8
[ 48.950775] __enqueue_rt_entity+0x320/0x360
[ 48.950805] enqueue_rt_entity+0x2c/0x44
[ 48.950805] enqueue_task_rt+0x24/0x94
[ 48.950836] ttwu_do_activate+0x54/0xc0
[ 48.950836] try_to_wake_up+0x248/0x5c8
[ 48.950836] __setup_irq+0x420/0x5f0
[ 48.950836] request_threaded_irq+0xdc/0x184
[ 48.950866] devm_request_threaded_irq+0x58/0xa4
[ 48.950866] omap_i2c_probe+0x530/0x6a0
[ 48.950897] platform_drv_probe+0x50/0xb0
[ 48.950897] driver_probe_device+0x1f8/0x2cc
[ 48.950897] __driver_attach+0xc0/0xc4
[ 48.950927] bus_for_each_dev+0x6c/0xa0
[ 48.950927] bus_add_driver+0x100/0x210
[ 48.950927] driver_register+0x78/0xf4
[ 48.950958] do_one_initcall+0x3c/0x16c
[ 48.950958] kernel_init_freeable+0x20c/0x2d8
[ 48.950958] kernel_init+0x8/0x110
[ 48.950988] ret_from_fork+0x14/0x24
[ 48.950988]
-> #4 (&rt_b->rt_runtime_lock){-.-...}:
[ 48.951019] _raw_spin_lock+0x40/0x50
[ 48.951019] rq_offline_rt+0x9c/0x2bc
[ 48.951019] set_rq_offline.part.2+0x2c/0x58
[ 48.951049] rq_attach_root+0x134/0x144
[ 48.951049] cpu_attach_domain+0x18c/0x6f4
[ 48.951049] build_sched_domains+0xba4/0xd80
[ 48.951080] sched_init_smp+0x68/0x10c
[ 48.951080] kernel_init_freeable+0x160/0x2d8
[ 48.951080] kernel_init+0x8/0x110
[ 48.951080] ret_from_fork+0x14/0x24
[ 48.951110]
-> #3 (&rq->lock){-.-.-.}:
[ 48.951110] _raw_spin_lock+0x40/0x50
[ 48.951141] task_fork_fair+0x30/0x124
[ 48.951141] sched_fork+0x194/0x2e0
[ 48.951141] copy_process.part.5+0x448/0x1a20
[ 48.951171] _do_fork+0x98/0x7e8
[ 48.951171] kernel_thread+0x2c/0x34
[ 48.951171] rest_init+0x1c/0x18c
[ 48.951202] start_kernel+0x35c/0x3d4
[ 48.951202] 0x8000807c
[ 48.951202]
-> #2 (&p->pi_lock){-.-.-.}:
[ 48.951232] _raw_spin_lock_irqsave+0x50/0x64
[ 48.951232] try_to_wake_up+0x30/0x5c8
[ 48.951232] up+0x4c/0x60
[ 48.951263] __up_console_sem+0x2c/0x58
[ 48.951263] console_unlock+0x3b4/0x650
[ 48.951263] vprintk_emit+0x270/0x474
[ 48.951293] vprintk_default+0x20/0x28
[ 48.951293] printk+0x20/0x30
[ 48.951324] kauditd_hold_skb+0x94/0xb8
[ 48.951324] kauditd_thread+0x1a4/0x56c
[ 48.951324] kthread+0x104/0x148
[ 48.951354] ret_from_fork+0x14/0x24
[ 48.951354]
-> #1 ((console_sem).lock){-.....}:
[ 48.951385] _raw_spin_lock_irqsave+0x50/0x64
[ 48.951385] down_trylock+0xc/0x2c
[ 48.951385] __down_trylock_console_sem+0x24/0x80
[ 48.951385] console_trylock+0x10/0x8c
[ 48.951416] vprintk_emit+0x264/0x474
[ 48.951416] vprintk_default+0x20/0x28
[ 48.951416] printk+0x20/0x30
[ 48.951446] tk_debug_account_sleep_time+0x5c/0x70
[ 48.951446] __timekeeping_inject_sleeptime.constprop.3+0x170/0x1a0
[ 48.951446] timekeeping_resume+0x218/0x23c
[ 48.951477] syscore_resume+0x94/0x42c
[ 48.951477] suspend_enter+0x554/0x9b4
[ 48.951477] suspend_devices_and_enter+0xd8/0x4b4
[ 48.951507] enter_state+0x934/0xbd4
[ 48.951507] pm_suspend+0x14/0x70
[ 48.951507] state_store+0x68/0xc8
[ 48.951538] kernfs_fop_write+0xf4/0x1f8
[ 48.951538] __vfs_write+0x1c/0x114
[ 48.951538] vfs_write+0xa0/0x168
[ 48.951568] SyS_write+0x3c/0x90
[ 48.951568] __sys_trace_return+0x0/0x10
[ 48.951568]
-> #0 (tk_core){----..}:
[ 48.951599] lock_acquire+0xe0/0x294
[ 48.951599] ktime_get_update_offsets_now+0x5c/0x1d4
[ 48.951629] retrigger_next_event+0x4c/0x90
[ 48.951629] on_each_cpu+0x40/0x7c
[ 48.951629] clock_was_set_work+0x14/0x20
[ 48.951660] process_one_work+0x2b4/0x808
[ 48.951660] worker_thread+0x3c/0x550
[ 48.951660] kthread+0x104/0x148
[ 48.951690] ret_from_fork+0x14/0x24
[ 48.951690]
other info that might help us debug this:
[ 48.951690] Chain exists of:
tk_core --> &rt_b->rt_runtime_lock --> hrtimer_bases.lock
[ 48.951721] Possible unsafe locking scenario:
[ 48.951721] CPU0 CPU1
[ 48.951721] ---- ----
[ 48.951721] lock(hrtimer_bases.lock);
[ 48.951751] lock(&rt_b->rt_runtime_lock);
[ 48.951751] lock(hrtimer_bases.lock);
[ 48.951751] lock(tk_core);
[ 48.951782]
*** DEADLOCK ***
[ 48.951782] 3 locks held by kworker/0:0/3:
[ 48.951782] #0: ("events"){.+.+.+}, at: [<c0156590>] process_one_work+0x1f8/0x808
[ 48.951812] #1: (hrtimer_work){+.+...}, at: [<c0156590>] process_one_work+0x1f8/0x808
[ 48.951843] #2: (hrtimer_bases.lock){-.-...}, at: [<c01cc610>] retrigger_next_event+0x38/0x90
[ 48.951843] stack backtrace:
[ 48.951873] CPU: 0 PID: 3 Comm: kworker/0:0 Not tainted 4.10.0-rc7-next-20170213+
[ 48.951904] Workqueue: events clock_was_set_work
[ 48.951904] [<c0110208>] (unwind_backtrace) from [<c010c224>] (show_stack+0x10/0x14)
[ 48.951934] [<c010c224>] (show_stack) from [<c04ca6c0>] (dump_stack+0xac/0xe0)
[ 48.951934] [<c04ca6c0>] (dump_stack) from [<c019b5cc>] (print_circular_bug+0x1d0/0x308)
[ 48.951965] [<c019b5cc>] (print_circular_bug) from [<c019d2a8>] (validate_chain+0xf50/0x1324)
[ 48.951965] [<c019d2a8>] (validate_chain) from [<c019ec18>] (__lock_acquire+0x468/0x7e8)
[ 48.951995] [<c019ec18>] (__lock_acquire) from [<c019f634>] (lock_acquire+0xe0/0x294)
[ 48.951995] [<c019f634>] (lock_acquire) from [<c01d0ea0>] (ktime_get_update_offsets_now+0x5c/0x1d4)
[ 48.952026] [<c01d0ea0>] (ktime_get_update_offsets_now) from [<c01cc624>] (retrigger_next_event+0x4c/0x90)
[ 48.952026] [<c01cc624>] (retrigger_next_event) from [<c01e4e24>] (on_each_cpu+0x40/0x7c)
[ 48.952056] [<c01e4e24>] (on_each_cpu) from [<c01cafc4>] (clock_was_set_work+0x14/0x20)
[ 48.952056] [<c01cafc4>] (clock_was_set_work) from [<c015664c>] (process_one_work+0x2b4/0x808)
[ 48.952087] [<c015664c>] (process_one_work) from [<c0157774>] (worker_thread+0x3c/0x550)
[ 48.952087] [<c0157774>] (worker_thread) from [<c015d644>] (kthread+0x104/0x148)
[ 48.952087] [<c015d644>] (kthread) from [<c0107830>] (ret_from_fork+0x14/0x24)
Replace printk() with printk_deferred(), which does not call into
the scheduler.
Fixes: 0bf43f15db85 ("timekeeping: Prints the amounts of time spent during suspend")
Reported-and-tested-by: Tony Lindgren <tony@xxxxxxxxxxx>
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: "Rafael J . Wysocki" <rjw@xxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/20170215044332.30449-1-sergey.senozhatsky@xxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/time/timekeeping_debug.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/kernel/time/timekeeping_debug.c
+++ b/kernel/time/timekeeping_debug.c
@@ -75,7 +75,7 @@ void tk_debug_account_sleep_time(struct
int bin = min(fls(t->tv_sec), NUM_BINS-1);
sleep_time_bin[bin]++;
- pr_info("Suspended for %lld.%03lu seconds\n", (s64)t->tv_sec,
- t->tv_nsec / NSEC_PER_MSEC);
+ printk_deferred(KERN_INFO "Suspended for %lld.%03lu seconds\n",
+ (s64)t->tv_sec, t->tv_nsec / NSEC_PER_MSEC);
}
Patches currently in stable-queue which might be from sergey.senozhatsky.work@xxxxxxxxx are
queue-4.9/timekeeping-use-deferred-printk-in-debug-code.patch
queue-4.9/printk-use-rcuidle-console-tracepoint.patch