[patch 155/166] kcov: use t->kcov_mode as enabled indicator

Andrew Morton
2020-04-07T03:12:20Z

From: Andrey Konovalov <andreyknvl@google.com>
Subject: 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.

Link: http://lkml.kernel.org/r/f70377945d1d8e6e4916cbce871a12303d6186b4.1585233617.git.andreyknvl@google.com
Link: http://lkml.kernel.org/r/ee1a1dec43059da5d7664c85c1addc89c4cd58de.1584655448.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Alexander Potapenko <glider@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Marco Elver <elver@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

kernel/kcov.c | 34 ++++++++++++++++++++++++----------
1 file changed, 24 insertions(+), 10 deletions(-)

--- a/kernel/kcov.c~kcov-use-t-kcov_mode-as-enabled-indicator
+++ a/kernel/kcov.c
@@ -746,26 +746,33 @@ static const struct file_operations kcov
* 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_mod
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)
- return;
+ 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);

_