Patch "timer/trace: Improve timer tracing" has been added to the 4.19-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    timer/trace: Improve timer tracing

to the 4.19-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:
     timer-trace-improve-timer-tracing.patch
and it can be found in the queue-4.19 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 8f8cbd582e9415845042fec6cb69b310fd4aebf8
Author: Anna-Maria Gleixner <anna-maria@xxxxxxxxxxxxx>
Date:   Thu Mar 21 13:09:21 2019 +0100

    timer/trace: Improve timer tracing
    
    [ Upstream commit f28d3d5346e97e60c81f933ac89ccf015430e5cf ]
    
    Timers are added to the timer wheel off by one. This is required in
    case a timer is queued directly before incrementing jiffies to prevent
    early timer expiry.
    
    When reading a timer trace and relying only on the expiry time of the timer
    in the timer_start trace point and on the now in the timer_expiry_entry
    trace point, it seems that the timer fires late. With the current
    timer_expiry_entry trace point information only now=jiffies is printed but
    not the value of base->clk. This makes it impossible to draw a conclusion
    to the index of base->clk and makes it impossible to examine timer problems
    without additional trace points.
    
    Therefore add the base->clk value to the timer_expire_entry trace
    point, to be able to calculate the index the timer base is located at
    during collecting expired timers.
    
    Signed-off-by: Anna-Maria Gleixner <anna-maria@xxxxxxxxxxxxx>
    Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
    Cc: fweisbec@xxxxxxxxx
    Cc: peterz@xxxxxxxxxxxxx
    Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
    Link: https://lkml.kernel.org/r/20190321120921.16463-5-anna-maria@xxxxxxxxxxxxx
    Stable-dep-of: 0f7352557a35 ("wifi: brcmfmac: Fix use-after-free bug in brcmf_cfg80211_detach")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/include/trace/events/timer.h b/include/trace/events/timer.h
index 8f6240854e28f..295517f109d71 100644
--- a/include/trace/events/timer.h
+++ b/include/trace/events/timer.h
@@ -89,24 +89,27 @@ TRACE_EVENT(timer_start,
  */
 TRACE_EVENT(timer_expire_entry,
 
-	TP_PROTO(struct timer_list *timer),
+	TP_PROTO(struct timer_list *timer, unsigned long baseclk),
 
-	TP_ARGS(timer),
+	TP_ARGS(timer, baseclk),
 
 	TP_STRUCT__entry(
 		__field( void *,	timer	)
 		__field( unsigned long,	now	)
 		__field( void *,	function)
+		__field( unsigned long,	baseclk	)
 	),
 
 	TP_fast_assign(
 		__entry->timer		= timer;
 		__entry->now		= jiffies;
 		__entry->function	= timer->function;
+		__entry->baseclk	= baseclk;
 	),
 
-	TP_printk("timer=%p function=%ps now=%lu",
-		  __entry->timer, __entry->function, __entry->now)
+	TP_printk("timer=%p function=%ps now=%lu baseclk=%lu",
+		  __entry->timer, __entry->function, __entry->now,
+		  __entry->baseclk)
 );
 
 /**
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index a6e88d9bb931c..140662c2b41e1 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1311,7 +1311,9 @@ int del_timer_sync(struct timer_list *timer)
 EXPORT_SYMBOL(del_timer_sync);
 #endif
 
-static void call_timer_fn(struct timer_list *timer, void (*fn)(struct timer_list *))
+static void call_timer_fn(struct timer_list *timer,
+			  void (*fn)(struct timer_list *),
+			  unsigned long baseclk)
 {
 	int count = preempt_count();
 
@@ -1334,7 +1336,7 @@ static void call_timer_fn(struct timer_list *timer, void (*fn)(struct timer_list
 	 */
 	lock_map_acquire(&lockdep_map);
 
-	trace_timer_expire_entry(timer);
+	trace_timer_expire_entry(timer, baseclk);
 	fn(timer);
 	trace_timer_expire_exit(timer);
 
@@ -1355,6 +1357,13 @@ static void call_timer_fn(struct timer_list *timer, void (*fn)(struct timer_list
 
 static void expire_timers(struct timer_base *base, struct hlist_head *head)
 {
+	/*
+	 * This value is required only for tracing. base->clk was
+	 * incremented directly before expire_timers was called. But expiry
+	 * is related to the old base->clk value.
+	 */
+	unsigned long baseclk = base->clk - 1;
+
 	while (!hlist_empty(head)) {
 		struct timer_list *timer;
 		void (*fn)(struct timer_list *);
@@ -1368,11 +1377,11 @@ static void expire_timers(struct timer_base *base, struct hlist_head *head)
 
 		if (timer->flags & TIMER_IRQSAFE) {
 			raw_spin_unlock(&base->lock);
-			call_timer_fn(timer, fn);
+			call_timer_fn(timer, fn, baseclk);
 			raw_spin_lock(&base->lock);
 		} else {
 			raw_spin_unlock_irq(&base->lock);
-			call_timer_fn(timer, fn);
+			call_timer_fn(timer, fn, baseclk);
 			raw_spin_lock_irq(&base->lock);
 		}
 	}