From: Andrey Konovalov <andreyk...@google.com>

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 instead
of just calling in_interrupt().

Link: 
http://lkml.kernel.org/r/1476115803-20712-1-git-send-email-andreyk...@google.com
Signed-off-by: Andrey Konovalov <andreyk...@google.com>
Acked-by: Dmitry Vyukov <dvyu...@google.com>
Cc: Nicolai Stange <nicsta...@gmail.com>
Cc: Andrey Ryabinin <aryabi...@virtuozzo.com>
Cc: Kees Cook <keesc...@chromium.org>
Cc: James Morse <james.mo...@arm.com>
Cc: Vegard Nossum <vegard.nos...@oracle.com>
Cc: Quentin Casasnovas <quentin.casasno...@oracle.com>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Andrey Ryabinin <aryabi...@virtuozzo.com>
---
 kernel/kcov.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 91b00e6..83b50fe 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -6,6 +6,7 @@
 #include <linux/file.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
+#include <linux/preempt_mask.h>
 #include <linux/printk.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
@@ -54,8 +55,15 @@ 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 || in_interrupt())
+       if (!t || (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_OFFSET
+                                                       | NMI_MASK)))
                return;
        mode = READ_ONCE(t->kcov_mode);
        if (mode == KCOV_MODE_TRACE) {
-- 
2.7.3

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