Re: [RFC][PATCH] hrtimer: Use printk_deferred_once for hrtimer_interrupt message

Thomas Gleixner
2024-02-22T15:17:22Z

On Wed, Feb 21 2024 at 21:12, John Stultz wrote:

Cc+ John. Keeping context intact,

> With qemu, I constantly see lockdep warnings after the
> hrimter_interrupt message is printed:
>
> [ 43.434557] hrtimer: interrupt took 6517564 ns
> [ 43.435000]
> [ 43.435000] =============================
> [ 43.435000] [ BUG: Invalid wait context ]

Do you have PROVE_RAW_LOCK_NESTING enabled?

> [ 43.435000] 6.8.0-rc5-00002-g28763ef29a5b #3743 Not tainted
> [ 43.435000] -----------------------------
> [ 43.435000] lock_torture_wr/605 is trying to lock:
> [ 43.435000] ffffffffbdcdc6f8 (&port_lock_key){-...}-{3:3}, at: serial8250_console_write+0xdd/0x710
> [ 43.435000] other info that might help us debug this:
> [ 43.435000] context-{2:2}
> [ 43.435000] 4 locks held by lock_torture_wr/605:
> [ 43.435000] #0: ffffffffbd6f1de8 (torture_mutex_init#4){+.+.}-{4:4}, at: torture_mutex_nested_lock+0x4b/0x70
> [ 43.435000] #1: ffffffffbb557260 (console_lock){+.+.}-{0:0}, at: vprintk_emit+0xd3/0x330
> [ 43.435000] #2: ffffffffbb5572d0 (console_srcu){....}-{0:0}, at: console_flush_all+0xd6/0x6b0
> [ 43.435000] #3: ffffffffbb396e20 (console_owner){-...}-{0:0}, at: console_flush_all+0x2a0/0x6b0
> [ 43.435000] stack backtrace:
> [ 43.435000] CPU: 36 PID: 605 Comm: lock_torture_wr Not tainted 6.8.0-rc5-00002-g28763ef29a5b #3743
> [ 43.435000] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> [ 43.435000] Call Trace:
> [ 43.435000] <IRQ>
> [ 43.435000] dump_stack_lvl+0x57/0x90
> [ 43.435000] __lock_acquire+0xd07/0x3260
> [ 43.435000] ? __pfx___lock_acquire+0x10/0x10
> [ 43.435000] ? memchr+0x1e/0x50
> [ 43.435000] lock_acquire+0x159/0x3b0
> [ 43.435000] ? serial8250_console_write+0xdd/0x710
> [ 43.435000] ? __pfx_lock_acquire+0x10/0x10
> [ 43.435000] ? __pfx___lock_acquire+0x10/0x10
> [ 43.435000] _raw_spin_lock_irqsave+0x42/0x60
> [ 43.435000] ? serial8250_console_write+0xdd/0x710
> [ 43.435000] serial8250_console_write+0xdd/0x710
> [ 43.435000] ? __pfx_serial8250_console_write+0x10/0x10
> [ 43.435000] ? __pfx_lock_release+0x10/0x10
> [ 43.435000] ? do_raw_spin_lock+0x104/0x180
> [ 43.435000] ? __pfx_do_raw_spin_lock+0x10/0x10
> [ 43.435000] ? console_flush_all+0x2a0/0x6b0
> [ 43.435000] console_flush_all+0x2ea/0x6b0
> [ 43.435000] ? console_flush_all+0x2a0/0x6b0
> [ 43.435000] ? __pfx_console_flush_all+0x10/0x10
> [ 43.435000] ? __pfx_lock_acquire+0x10/0x10
> [ 43.435000] console_unlock+0x9d/0x150
> [ 43.435000] ? __pfx_console_unlock+0x10/0x10
> [ 43.435000] ? vprintk_emit+0xd3/0x330
> [ 43.435000] ? __down_trylock_console_sem+0x62/0xa0
> [ 43.435000] ? vprintk_emit+0xd3/0x330
> [ 43.435000] vprintk_emit+0xdc/0x330
> [ 43.435000] _printk+0x92/0xb0
> [ 43.435000] ? __pfx__printk+0x10/0x10
> [ 43.435000] ? hrtimer_interrupt+0x2f0/0x360
> [ 43.439262] __sysvec_apic_timer_interrupt+0xb8/0x290
> [ 43.439345] sysvec_apic_timer_interrupt+0x8a/0xb0
> [ 43.439345] </IRQ>
> [ 43.439345] <TASK>
> [ 43.439345] asm_sysvec_apic_timer_interrupt+0x16/0x20
>
> I thought the new printk work was going to resolve this, but
> apparently not, so to avoid trying to printk in this problematic
> context, lets use prink_deferred_once() instead.
>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Frederic Weisbecker <frederic@kernel.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: kernel-team@android.com
> Signed-off-by: John Stultz <jstultz@google.com>
> ---
> kernel/time/hrtimer.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
> index edb0f821dcea..e6b060403384 100644
> --- a/kernel/time/hrtimer.c
> +++ b/kernel/time/hrtimer.c
> @@ -1870,7 +1870,8 @@ void hrtimer_interrupt(struct clock_event_device *dev)
> else
> expires_next = ktime_add(now, delta);
> tick_program_event(expires_next, 1);
> - pr_warn_once("hrtimer: interrupt took %llu ns\n", ktime_to_ns(delta));
> + printk_deferred_once(KERN_WARNING "hrtimer: interrupt took %llu ns\n",
> + ktime_to_ns(delta));
> }
>
> /* called with interrupts disabled */