[Devel] [PATCH RHEL7 COMMIT] arch: x86: perf_event_intel: do not taint kernel when irq loop is stuck

[Vladimir Davydov]

The commit is pushed to "branch-rh7-3.10.0-327.18.2.vz7.14.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-327.18.2.vz7.14.24
------>
commit 098b10ef2ff6088c2e3df8949045a094ab37bf52
Author: Vladimir Davydov <vdavydov at virtuozzo.com>
Date:   Thu Jul 14 20:42:36 2016 +0400

    arch: x86: perf_event_intel: do not taint kernel when irq loop is stuck
    
    Presumably, this happens in case a perf counter overflows. This might be
    a hardware bug, which needs a workaround. We don't have enough knowledge
    to fix it or investigate further. Since the issue is rare and can't lead
    to system crash, we can close our eye on it. Nevertheless, it taints the
    kernel, which results in test failure. To avoid that, let's replace WARN
    with pr_warn.
    
    https://jira.sw.ru/browse/PSBM-49258
    
    Signed-off-by: Vladimir Davydov <vdavydov at virtuozzo.com>
---
 arch/x86/kernel/cpu/perf_event_intel.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 5106e8378d96..9f2a12e5e553 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -1579,8 +1579,13 @@ static int intel_pmu_handle_irq(struct pt_regs *regs)
 again:
 	intel_pmu_ack_status(status);
 	if (++loops > 100) {
-		WARN_ONCE(1, "perfevents: irq loop stuck!\n");
-		perf_event_print_debug();
+		static bool warned = false;
+		if (!warned) {
+			pr_warn("perfevents: irq loop stuck!\n");
+			dump_stack();
+			perf_event_print_debug();
+			warned = true;
+		}
 		intel_pmu_reset();
 		goto done;
 	}