Patch "Revert "perf/core: Drop kernel samples even though :u is specified"" has been added to the 4.12-stable tree

[<gregkh@linuxfoundation.org>]

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

    Revert "perf/core: Drop kernel samples even though :u is specified"

to the 4.12-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:
     revert-perf-core-drop-kernel-samples-even-though-u-is-specified.patch
and it can be found in the queue-4.12 subdirectory.

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


>From 6a8a75f3235724c5941a33e287b2f98966ad14c5 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@kernel.org>
Date: Tue, 11 Jul 2017 10:56:54 +0200
Subject: Revert "perf/core: Drop kernel samples even though :u is specified"

From: Ingo Molnar <mingo@kernel.org>

commit 6a8a75f3235724c5941a33e287b2f98966ad14c5 upstream.

This reverts commit cc1582c231ea041fbc68861dfaf957eaf902b829.

This commit introduced a regression that broke rr-project, which uses sampling
events to receive a signal on overflow (but does not care about the contents
of the sample). These signals are critical to the correct operation of rr.

There's been some back and forth about how to fix it - but to not keep
applications in limbo queue up a revert.

Reported-by: Kyle Huey <me@kylehuey.com>
Acked-by: Kyle Huey <me@kylehuey.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/20170628105600.GC5981@leverpostej
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/events/core.c |   21 ---------------------
 1 file changed, 21 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7323,21 +7323,6 @@ int perf_event_account_interrupt(struct
 	return __perf_event_account_interrupt(event, 1);
 }
 
-static bool sample_is_allowed(struct perf_event *event, struct pt_regs *regs)
-{
-	/*
-	 * Due to interrupt latency (AKA "skid"), we may enter the
-	 * kernel before taking an overflow, even if the PMU is only
-	 * counting user events.
-	 * To avoid leaking information to userspace, we must always
-	 * reject kernel samples when exclude_kernel is set.
-	 */
-	if (event->attr.exclude_kernel && !user_mode(regs))
-		return false;
-
-	return true;
-}
-
 /*
  * Generic event overflow handling, sampling.
  */
@@ -7359,12 +7344,6 @@ static int __perf_event_overflow(struct
 	ret = __perf_event_account_interrupt(event, throttle);
 
 	/*
-	 * For security, drop the skid kernel samples if necessary.
-	 */
-	if (!sample_is_allowed(event, regs))
-		return ret;
-
-	/*
 	 * XXX event_limit might not quite work as expected on inherited
 	 * events
 	 */


Patches currently in stable-queue which might be from mingo@kernel.org are

queue-4.12/x86-ioapic-pass-the-correct-data-to-unmask_ioapic_irq.patch
queue-4.12/perf-core-fix-scheduling-regression-of-pinned-groups.patch
queue-4.12/x86-acpi-prevent-out-of-bound-access-caused-by-broken-acpi-tables.patch
queue-4.12/revert-perf-core-drop-kernel-samples-even-though-u-is-specified.patch