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

BugLink: http://bugs.launchpad.net/bugs/1707233
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>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 22350b15b4e7a3d4017c3eea271d1c7dd19c116b..784ab8fe8714c53a3b3f1a4af58542e0a0413a68 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6410,21 +6410,6 @@ static void perf_log_itrace_start(struct perf_event *event)
        perf_output_end(&handle);
 }
 
-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.
  */
@@ -6471,12 +6456,6 @@ static int __perf_event_overflow(struct perf_event *event,
                        perf_adjust_period(event, delta, hwc->last_period, true);
        }
 
-       /*
-        * 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