mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-25 21:54:06 +08:00
aafe104aa9
It was reported that a fix to the ring buffer recursion detection would cause a hung machine when performing suspend / resume testing. The following backtrace was extracted from debugging that case: Call Trace: trace_clock_global+0x91/0xa0 __rb_reserve_next+0x237/0x460 ring_buffer_lock_reserve+0x12a/0x3f0 trace_buffer_lock_reserve+0x10/0x50 __trace_graph_return+0x1f/0x80 trace_graph_return+0xb7/0xf0 ? trace_clock_global+0x91/0xa0 ftrace_return_to_handler+0x8b/0xf0 ? pv_hash+0xa0/0xa0 return_to_handler+0x15/0x30 ? ftrace_graph_caller+0xa0/0xa0 ? trace_clock_global+0x91/0xa0 ? __rb_reserve_next+0x237/0x460 ? ring_buffer_lock_reserve+0x12a/0x3f0 ? trace_event_buffer_lock_reserve+0x3c/0x120 ? trace_event_buffer_reserve+0x6b/0xc0 ? trace_event_raw_event_device_pm_callback_start+0x125/0x2d0 ? dpm_run_callback+0x3b/0xc0 ? pm_ops_is_empty+0x50/0x50 ? platform_get_irq_byname_optional+0x90/0x90 ? trace_device_pm_callback_start+0x82/0xd0 ? dpm_run_callback+0x49/0xc0 With the following RIP: RIP: 0010:native_queued_spin_lock_slowpath+0x69/0x200 Since the fix to the recursion detection would allow a single recursion to happen while tracing, this lead to the trace_clock_global() taking a spin lock and then trying to take it again: ring_buffer_lock_reserve() { trace_clock_global() { arch_spin_lock() { queued_spin_lock_slowpath() { /* lock taken */ (something else gets traced by function graph tracer) ring_buffer_lock_reserve() { trace_clock_global() { arch_spin_lock() { queued_spin_lock_slowpath() { /* DEAD LOCK! */ Tracing should *never* block, as it can lead to strange lockups like the above. Restructure the trace_clock_global() code to instead of simply taking a lock to update the recorded "prev_time" simply use it, as two events happening on two different CPUs that calls this at the same time, really doesn't matter which one goes first. Use a trylock to grab the lock for updating the prev_time, and if it fails, simply try again the next time. If it failed to be taken, that means something else is already updating it. Link: https://lkml.kernel.org/r/20210430121758.650b6e8a@gandalf.local.home Cc: stable@vger.kernel.org Tested-by: Konstantin Kharlamov <hi-angel@yandex.ru> Tested-by: Todd Brandt <todd.e.brandt@linux.intel.com> Fixes:b02414c8f0
("ring-buffer: Fix recursion protection transitions between interrupt context") # started showing the problem Fixes:14131f2f98
("tracing: implement trace_clock_*() APIs") # where the bug happened Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=212761 Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
159 lines
4.2 KiB
C
159 lines
4.2 KiB
C
// SPDX-License-Identifier: GPL-2.0
|
|
/*
|
|
* tracing clocks
|
|
*
|
|
* Copyright (C) 2009 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
|
|
*
|
|
* Implements 3 trace clock variants, with differing scalability/precision
|
|
* tradeoffs:
|
|
*
|
|
* - local: CPU-local trace clock
|
|
* - medium: scalable global clock with some jitter
|
|
* - global: globally monotonic, serialized clock
|
|
*
|
|
* Tracer plugins will chose a default from these clocks.
|
|
*/
|
|
#include <linux/spinlock.h>
|
|
#include <linux/irqflags.h>
|
|
#include <linux/hardirq.h>
|
|
#include <linux/module.h>
|
|
#include <linux/percpu.h>
|
|
#include <linux/sched.h>
|
|
#include <linux/sched/clock.h>
|
|
#include <linux/ktime.h>
|
|
#include <linux/trace_clock.h>
|
|
|
|
/*
|
|
* trace_clock_local(): the simplest and least coherent tracing clock.
|
|
*
|
|
* Useful for tracing that does not cross to other CPUs nor
|
|
* does it go through idle events.
|
|
*/
|
|
u64 notrace trace_clock_local(void)
|
|
{
|
|
u64 clock;
|
|
|
|
/*
|
|
* sched_clock() is an architecture implemented, fast, scalable,
|
|
* lockless clock. It is not guaranteed to be coherent across
|
|
* CPUs, nor across CPU idle events.
|
|
*/
|
|
preempt_disable_notrace();
|
|
clock = sched_clock();
|
|
preempt_enable_notrace();
|
|
|
|
return clock;
|
|
}
|
|
EXPORT_SYMBOL_GPL(trace_clock_local);
|
|
|
|
/*
|
|
* trace_clock(): 'between' trace clock. Not completely serialized,
|
|
* but not completely incorrect when crossing CPUs either.
|
|
*
|
|
* This is based on cpu_clock(), which will allow at most ~1 jiffy of
|
|
* jitter between CPUs. So it's a pretty scalable clock, but there
|
|
* can be offsets in the trace data.
|
|
*/
|
|
u64 notrace trace_clock(void)
|
|
{
|
|
return local_clock();
|
|
}
|
|
EXPORT_SYMBOL_GPL(trace_clock);
|
|
|
|
/*
|
|
* trace_jiffy_clock(): Simply use jiffies as a clock counter.
|
|
* Note that this use of jiffies_64 is not completely safe on
|
|
* 32-bit systems. But the window is tiny, and the effect if
|
|
* we are affected is that we will have an obviously bogus
|
|
* timestamp on a trace event - i.e. not life threatening.
|
|
*/
|
|
u64 notrace trace_clock_jiffies(void)
|
|
{
|
|
return jiffies_64_to_clock_t(jiffies_64 - INITIAL_JIFFIES);
|
|
}
|
|
EXPORT_SYMBOL_GPL(trace_clock_jiffies);
|
|
|
|
/*
|
|
* trace_clock_global(): special globally coherent trace clock
|
|
*
|
|
* It has higher overhead than the other trace clocks but is still
|
|
* an order of magnitude faster than GTOD derived hardware clocks.
|
|
*
|
|
* Used by plugins that need globally coherent timestamps.
|
|
*/
|
|
|
|
/* keep prev_time and lock in the same cacheline. */
|
|
static struct {
|
|
u64 prev_time;
|
|
arch_spinlock_t lock;
|
|
} trace_clock_struct ____cacheline_aligned_in_smp =
|
|
{
|
|
.lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED,
|
|
};
|
|
|
|
u64 notrace trace_clock_global(void)
|
|
{
|
|
unsigned long flags;
|
|
int this_cpu;
|
|
u64 now, prev_time;
|
|
|
|
raw_local_irq_save(flags);
|
|
|
|
this_cpu = raw_smp_processor_id();
|
|
|
|
/*
|
|
* The global clock "guarantees" that the events are ordered
|
|
* between CPUs. But if two events on two different CPUS call
|
|
* trace_clock_global at roughly the same time, it really does
|
|
* not matter which one gets the earlier time. Just make sure
|
|
* that the same CPU will always show a monotonic clock.
|
|
*
|
|
* Use a read memory barrier to get the latest written
|
|
* time that was recorded.
|
|
*/
|
|
smp_rmb();
|
|
prev_time = READ_ONCE(trace_clock_struct.prev_time);
|
|
now = sched_clock_cpu(this_cpu);
|
|
|
|
/* Make sure that now is always greater than prev_time */
|
|
if ((s64)(now - prev_time) < 0)
|
|
now = prev_time + 1;
|
|
|
|
/*
|
|
* If in an NMI context then dont risk lockups and simply return
|
|
* the current time.
|
|
*/
|
|
if (unlikely(in_nmi()))
|
|
goto out;
|
|
|
|
/* Tracing can cause strange recursion, always use a try lock */
|
|
if (arch_spin_trylock(&trace_clock_struct.lock)) {
|
|
/* Reread prev_time in case it was already updated */
|
|
prev_time = READ_ONCE(trace_clock_struct.prev_time);
|
|
if ((s64)(now - prev_time) < 0)
|
|
now = prev_time + 1;
|
|
|
|
trace_clock_struct.prev_time = now;
|
|
|
|
/* The unlock acts as the wmb for the above rmb */
|
|
arch_spin_unlock(&trace_clock_struct.lock);
|
|
}
|
|
out:
|
|
raw_local_irq_restore(flags);
|
|
|
|
return now;
|
|
}
|
|
EXPORT_SYMBOL_GPL(trace_clock_global);
|
|
|
|
static atomic64_t trace_counter;
|
|
|
|
/*
|
|
* trace_clock_counter(): simply an atomic counter.
|
|
* Use the trace_counter "counter" for cases where you do not care
|
|
* about timings, but are interested in strict ordering.
|
|
*/
|
|
u64 notrace trace_clock_counter(void)
|
|
{
|
|
return atomic64_add_return(1, &trace_counter);
|
|
}
|