Commit f3c0eba2 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

perf: Add a few assertions 



While auditing 6b959ba2 ("perf/core: Fix reentry problem in
perf_output_read_group()") a few spots were found that wanted
assertions.

Notable for_each_sibling_event() relies on exclusion from
modification. This would normally be holding either ctx->lock or
ctx->mutex, however due to how things are constructed disabling IRQs
is a valid and sufficient substitute for ctx->lock.

Another possible site to add assertions would be the various
pmu::{add,del,read,..}() methods, but that's not trivially expressable
in C -- the best option is wrappers, but those are easy enough to
forget.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
parent 88081cfb

include/linux/perf_event.h

+17 −0
Original line number Diff line number Diff line
@@ -61,6 +61,7 @@ struct perf_guest_info_callbacks { 
#include <linux/refcount.h>

#include <linux/security.h>

#include <linux/static_call.h>

#include <linux/lockdep.h>

#include <asm/local.h>



struct perf_callchain_entry {
@@ -634,7 +635,23 @@ struct pmu_event_list { 
	struct list_head	list;

};



/*

 * event->sibling_list is modified whole holding both ctx->lock and ctx->mutex

 * as such iteration must hold either lock. However, since ctx->lock is an IRQ

 * safe lock, and is only held by the CPU doing the modification, having IRQs

 * disabled is sufficient since it will hold-off the IPIs.

 */

#ifdef CONFIG_PROVE_LOCKING

#define lockdep_assert_event_ctx(event)				\

	WARN_ON_ONCE(__lockdep_enabled &&			\

		     (this_cpu_read(hardirqs_enabled) ||	\

		      lockdep_is_held(&(event)->ctx->mutex) != LOCK_STATE_HELD))

#else

#define lockdep_assert_event_ctx(event)

#endif



#define for_each_sibling_event(sibling, event)			\

	lockdep_assert_event_ctx(event);			\

	if ((event)->group_leader == (event))			\

		list_for_each_entry((sibling), &(event)->sibling_list, sibling_list)

kernel/events/core.c

+2 −0
Original line number Diff line number Diff line
@@ -1468,6 +1468,8 @@ static void __update_context_time(struct perf_event_context *ctx, bool adv) 
{

	u64 now = perf_clock();



	lockdep_assert_held(&ctx->lock);



	if (adv)

		ctx->time += now - ctx->timestamp;

	ctx->timestamp = now;