linux-kernel - [PATCH v4 5/7] kcov: use t->kcov

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Date:   Thu, 26 Mar 2020 15:44:04 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: [PATCH v4 5/7] kcov: use t->kcov_mode as enabled indicator

Currently kcov_remote_start() and kcov_remote_stop() check t->kcov to
find out whether the coverage is already being collected by the
current task. Use t->kcov_mode for that instead. This doesn't change
the overall behavior in any way, but serves as a preparation for the
following softirq coverage collection support patch.

Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
---
 kernel/kcov.c | 32 +++++++++++++++++++++++---------
 1 file changed, 23 insertions(+), 9 deletions(-)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index b985b7a72870..e43f06b5b2e4 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -746,26 +746,33 @@ static const struct file_operations kcov_fops = {
  * In turns kcov_remote_stop() clears those pointers from task_struct to stop
  * collecting coverage and copies all collected coverage into the kcov area.
  */
+
+static inline bool kcov_mode_enabled(unsigned int mode)
+{
+	return (mode & ~KCOV_IN_CTXSW) != KCOV_MODE_DISABLED;
+}
+
 void kcov_remote_start(u64 handle)
 {
+	struct task_struct *t = current;
 	struct kcov_remote *remote;
 	struct kcov *kcov;
+	unsigned int mode;
 	void *area;
-	struct task_struct *t;
 	unsigned int size;
-	enum kcov_mode mode;
 	int sequence;
 
 	if (WARN_ON(!kcov_check_handle(handle, true, true, true)))
 		return;
 	if (WARN_ON(!in_task()))
 		return;
-	t = current;
+
 	/*
 	 * Check that kcov_remote_start is not called twice
 	 * nor called by user tasks (with enabled kcov).
 	 */
-	if (WARN_ON(t->kcov))
+	mode = READ_ONCE(t->kcov_mode);
+	if (WARN_ON(kcov_mode_enabled(mode)))
 		return;
 
 	kcov_debug("handle = %llx\n", handle);
@@ -863,13 +870,20 @@ static void kcov_move_area(enum kcov_mode mode, void *dst_area,
 void kcov_remote_stop(void)
 {
 	struct task_struct *t = current;
-	struct kcov *kcov = t->kcov;
-	void *area = t->kcov_area;
-	unsigned int size = t->kcov_size;
-	int sequence = t->kcov_sequence;
+	struct kcov *kcov;
+	unsigned int mode;
+	void *area;
+	unsigned int size;
+	int sequence;
 
-	if (!kcov)
+	mode = READ_ONCE(t->kcov_mode);
+	barrier();
+	if (!kcov_mode_enabled(mode))
 		return;
+	kcov = t->kcov;
+	area = t->kcov_area;
+	size = t->kcov_size;
+	sequence = t->kcov_sequence;
 
 	kcov_stop(t);
 
-- 
2.26.0.rc2.310.g2932bb562d-goog