linux-kernel - [PATCH] kcov: simplify interrupt check

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Date:   Tue, 21 Mar 2017 10:10:26 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     akpm@...ux-foundation.org, linux-mm@...ck.org
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        James Morse <james.morse@....com>,
        Alexander Popov <alex.popov@...ux.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        linux-kernel@...r.kernel.org, syzkaller@...glegroups.com
Subject: [PATCH] kcov: simplify interrupt check

in_interrupt() semantics are confusing and wrong for most users
as it also returns true when bh is disabled. Thus we open coded
a proper check for interrupts in __sanitizer_cov_trace_pc()
with a lengthy explanatory comment.

Use the new in_task() predicate instead.

Signed-off-by: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Kefeng Wang <wangkefeng.wang@...wei.com>
Cc: James Morse <james.morse@....com>
Cc: Alexander Popov <alex.popov@...ux.com>
Cc: Andrey Konovalov <andreyknvl@...gle.com>
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org
Cc: syzkaller@...glegroups.com
---
 kernel/kcov.c | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 85e5546cd791..cd771993f96f 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -60,15 +60,8 @@ 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.
-	 * The checks for whether we are in an interrupt are open-coded, because
-	 * 1. We can't use in_interrupt() here, since it also returns true
-	 *    when we are inside local_bh_disable() section.
-	 * 2. We don't want to use (in_irq() | in_serving_softirq() | in_nmi()),
-	 *    since that leads to slower generated code (three separate tests,
-	 *    one for each of the flags).
 	 */
-	if (!t || (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_OFFSET
-							| NMI_MASK)))
+	if (!t || !in_task())
 		return;
 	mode = READ_ONCE(t->kcov_mode);
 	if (mode == KCOV_MODE_TRACE) {
-- 
2.12.1.500.gab5fba24ee-goog