Patch "perf/core: Fix perf_sched_count derailment" has been added to the 4.5-stable tree

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

perf/core: Fix perf_sched_count derailment

to the 4.5-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:
perf-core-fix-perf_sched_count-derailment.patch
and it can be found in the queue-4.5 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Alexander Shishkin <[email protected]>
Date: Wed, 2 Mar 2016 13:24:14 +0200
Subject: perf/core: Fix perf_sched_count derailment

From: Alexander Shishkin <[email protected]>

commit 927a5570855836e5d5859a80ce7e91e963545e8f upstream.

The error path in perf_event_open() is such that asking for a sampling event on a PMU that doesn't generate interrupts will end up in dropping the perf_sched_count even though it hasn't been incremented for this event yet.

Given a sufficient amount of these calls, we'll end up disabling scheduler's jump label even though we'd still have active events in the system, thereby facilitating the arrival of the infernal regions upon us.

I'm fixing this by moving account_event() inside perf_event_alloc().

---
 kernel/events/core.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

@@ -8001,6 +8001,9 @@ perf_event_alloc(struct perf_event_attr
 		}
 	}
 
+	/* symmetric to unaccount_event() in _free_event() */
+	account_event(event);
+
 	return event;
 
 err_per_task:

@@ -8364,8 +8367,6 @@ SYSCALL_DEFINE5(perf_event_open,
 		}
 	}
 
-	account_event(event);
-
 	/*
 	 * Special case software events and allow them to be part of
 	 * any hardware group.

@@ -8662,8 +8663,6 @@ perf_event_create_kernel_counter(struct
 	/* Mark owner so we could distinguish it from user events. */
 	event->owner = TASK_TOMBSTONE;
 
-	account_event(event);
-
 	ctx = find_get_context(event->pmu, task, event);
 	if (IS_ERR(ctx)) {
 		err = PTR_ERR(ctx);

Patches currently in stable-queue which might be from [email protected] are

queue-4.5/perf-x86-intel-add-definition-for-pt-pmi-bit.patch queue-4.5/perf-core-fix-perf_sched_count-derailment.patch