linux-kernel - [PATCH] kcov: properly check if we are in an interrupt

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Message-Id: <1474642273-112248-1-git-send-email-andreyknvl@google.com>
Date:   Fri, 23 Sep 2016 16:51:13 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Nicolai Stange <nicstange@...il.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Kees Cook <keescook@...omium.org>,
        James Morse <james.morse@....com>,
        linux-kernel@...r.kernel.org, vegard.nossum@...cle.com,
        quentin.casasnovas@...cle.com, ryabinin.a.a@...il.com
Cc:     Andrey Konovalov <andreyknvl@...gle.com>
Subject: [PATCH] kcov: properly check if we are in an interrupt

in_interrupt() returns a nonzero value when we are either in an
interrupt or have bh disabled via local_bh_disable(). Since we are
interested in only ignoring coverage from actual interrupts, do a
proper check of whether we are really in an interrupt.

Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
---
It would look totally better to reuse in_irq(), in_serving_softirq() and
in_nmi() instead of checking flags manually, but that leads to slower
generated code (three separate tests for each of the flags). Would it be
better to add another macro to preempt.h that would check if we're actually
in interrupt and use it?

 kernel/kcov.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 8d44b3f..47c35a8 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -54,7 +54,8 @@ void notrace __sanitizer_cov_trace_pc(void)
 	 * We are interested in code coverage as a function of a syscall inputs,
 	 * so we ignore code executed in interrupts.
 	 */
-	if (!t || in_interrupt())
+	if (!t || (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_OFFSET
+							| NMI_MASK)))
 		return;
 	mode = READ_ONCE(t->kcov_mode);
 	if (mode == KCOV_MODE_TRACE) {
-- 
2.8.0.rc3.226.g39d4020