On Tue, Jan 09, 2018 at 04:12:53PM +0100, Peter Zijlstra wrote:
> In any case, I found yet another lockdep splat, trying to figure out wth
> to do about that.
An of course, testing this one yields yet another lockdep splat..
onwards to #3 :/
---
Subject: perf: Fix another perf,trace,cpuhp lock inversion
From: Peter Zijlstra <pet...@infradead.org>
Date: Tue Jan 9 17:07:59 CET 2018
Lockdep complained about:
perf_trace_init()
#0 mutex_lock(&event_mutex)
perf_trace_event_init()
perf_trace_event_reg()
tp_event->class->reg() := tracepoint_probe_register
#1 mutex_lock(&tracepoints_mutex)
trace_point_add_func()
#2 static_key_enable()
#2 do_cpu_up()
perf_event_init_cpu()
#3 mutex_lock(&pmus_lock)
#4 mutex_lock(&ctx->mutex)
perf_ioctl()
#4 ctx = perf_event_ctx_lock()
_perf_iotcl()
ftrace_profile_set_filter()
#0 mutex_lock(&event_mutex)
Fudge it for now by noting that the tracepoint state does not depend
on the event <-> context relation. Ugly though :/
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Steven Rostedt <rost...@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
kernel/events/core.c | 26 ++++++++++++++++++++++++--
1 file changed, 24 insertions(+), 2 deletions(-)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -8525,6 +8525,29 @@ perf_event_set_addr_filter(struct perf_e
return ret;
}
+static int
+perf_tracepoint_set_filter(struct perf_event *event, char *filter_str)
+{
+ struct perf_event_context *ctx = event->ctx;
+ int ret;
+
+ /*
+ * Beware, here be dragons!!
+ *
+ * the tracepoint muck will deadlock against ctx->mutex, but the
tracepoint
+ * stuff does not actually need it. So temporarily drop ctx->mutex. As
per
+ * perf_event_ctx_lock() we already have a reference on ctx.
+ *
+ * This can result in event getting moved to a different ctx, but that
+ * does not affect the tracepoint state.
+ */
+ mutex_unlock(&ctx->mutex);
+ ret = ftrace_profile_set_filter(event, event->attr.config, filter_str);
+ mutex_lock(&ctx->mutex);
+
+ return ret;
+}
+
static int perf_event_set_filter(struct perf_event *event, void __user *arg)
{
char *filter_str;
@@ -8541,8 +8564,7 @@ static int perf_event_set_filter(struct
if (IS_ENABLED(CONFIG_EVENT_TRACING) &&
event->attr.type == PERF_TYPE_TRACEPOINT)
- ret = ftrace_profile_set_filter(event, event->attr.config,
- filter_str);
+ ret = perf_tracepoint_set_filter(event, filter_str);
else if (has_addr_filter(event))
ret = perf_event_set_addr_filter(event, filter_str);
