129 lines
4.3 KiB
Diff
129 lines
4.3 KiB
Diff
From: Steven Rostedt <rostedt@goodmis.org>
|
|
Date: Fri, 22 Sep 2017 14:58:15 -0500
|
|
Subject: [PATCH 01/42] tracing: Steve's unofficial trace_recursive_lock()
|
|
patch
|
|
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.14/older/patches-4.14.1-rt3.tar.xz
|
|
|
|
On Tue, 5 Sep 2017 16:57:52 -0500
|
|
Tom Zanussi <tom.zanussi@linux.intel.com> wrote:
|
|
|
|
> Synthetic event generation requires the reservation of a second event
|
|
> while the reservation of a previous event is still in progress. The
|
|
> trace_recursive_lock() check in ring_buffer_lock_reserve() prevents
|
|
> this however.
|
|
>
|
|
> This sets up a special reserve pathway for this particular case,
|
|
> leaving existing pathways untouched, other than an additional check in
|
|
> ring_buffer_lock_reserve() and trace_event_buffer_reserve(). These
|
|
> checks could be gotten rid of as well, with copies of those functions,
|
|
> but for now try to avoid that unless necessary.
|
|
>
|
|
> Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
|
|
|
|
I've been planing on changing that lock, which may help you here
|
|
without having to mess around with parameters. That is to simply add a
|
|
counter. Would this patch help you. You can add a patch to increment
|
|
the count to 5 with an explanation of handling synthetic events, but
|
|
even getting to 4 is extremely unlikely.
|
|
|
|
I'll make this into an official patch if this works for you, and then
|
|
you can include it in your series.
|
|
|
|
-- Steve
|
|
|
|
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
---
|
|
kernel/trace/ring_buffer.c | 66 ++++++++++++---------------------------------
|
|
1 file changed, 18 insertions(+), 48 deletions(-)
|
|
|
|
--- a/kernel/trace/ring_buffer.c
|
|
+++ b/kernel/trace/ring_buffer.c
|
|
@@ -2538,61 +2538,29 @@ rb_wakeups(struct ring_buffer *buffer, s
|
|
* The lock and unlock are done within a preempt disable section.
|
|
* The current_context per_cpu variable can only be modified
|
|
* by the current task between lock and unlock. But it can
|
|
- * be modified more than once via an interrupt. To pass this
|
|
- * information from the lock to the unlock without having to
|
|
- * access the 'in_interrupt()' functions again (which do show
|
|
- * a bit of overhead in something as critical as function tracing,
|
|
- * we use a bitmask trick.
|
|
+ * be modified more than once via an interrupt. There are four
|
|
+ * different contexts that we need to consider.
|
|
*
|
|
- * bit 0 = NMI context
|
|
- * bit 1 = IRQ context
|
|
- * bit 2 = SoftIRQ context
|
|
- * bit 3 = normal context.
|
|
- *
|
|
- * This works because this is the order of contexts that can
|
|
- * preempt other contexts. A SoftIRQ never preempts an IRQ
|
|
- * context.
|
|
- *
|
|
- * When the context is determined, the corresponding bit is
|
|
- * checked and set (if it was set, then a recursion of that context
|
|
- * happened).
|
|
- *
|
|
- * On unlock, we need to clear this bit. To do so, just subtract
|
|
- * 1 from the current_context and AND it to itself.
|
|
- *
|
|
- * (binary)
|
|
- * 101 - 1 = 100
|
|
- * 101 & 100 = 100 (clearing bit zero)
|
|
- *
|
|
- * 1010 - 1 = 1001
|
|
- * 1010 & 1001 = 1000 (clearing bit 1)
|
|
- *
|
|
- * The least significant bit can be cleared this way, and it
|
|
- * just so happens that it is the same bit corresponding to
|
|
- * the current context.
|
|
+ * Normal context.
|
|
+ * SoftIRQ context
|
|
+ * IRQ context
|
|
+ * NMI context
|
|
+ *
|
|
+ * If for some reason the ring buffer starts to recurse, we
|
|
+ * only allow that to happen at most 4 times (one for each
|
|
+ * context). If it happens 5 times, then we consider this a
|
|
+ * recusive loop and do not let it go further.
|
|
*/
|
|
|
|
static __always_inline int
|
|
trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer)
|
|
{
|
|
- unsigned int val = cpu_buffer->current_context;
|
|
- int bit;
|
|
-
|
|
- if (in_interrupt()) {
|
|
- if (in_nmi())
|
|
- bit = RB_CTX_NMI;
|
|
- else if (in_irq())
|
|
- bit = RB_CTX_IRQ;
|
|
- else
|
|
- bit = RB_CTX_SOFTIRQ;
|
|
- } else
|
|
- bit = RB_CTX_NORMAL;
|
|
-
|
|
- if (unlikely(val & (1 << bit)))
|
|
+ if (cpu_buffer->current_context >= 4)
|
|
return 1;
|
|
|
|
- val |= (1 << bit);
|
|
- cpu_buffer->current_context = val;
|
|
+ cpu_buffer->current_context++;
|
|
+ /* Interrupts must see this update */
|
|
+ barrier();
|
|
|
|
return 0;
|
|
}
|
|
@@ -2600,7 +2568,9 @@ trace_recursive_lock(struct ring_buffer_
|
|
static __always_inline void
|
|
trace_recursive_unlock(struct ring_buffer_per_cpu *cpu_buffer)
|
|
{
|
|
- cpu_buffer->current_context &= cpu_buffer->current_context - 1;
|
|
+ /* Don't let the dec leak out */
|
|
+ barrier();
|
|
+ cpu_buffer->current_context--;
|
|
}
|
|
|
|
/**
|