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@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Dmitry Vyukov <dvyukov@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>
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: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 7cd05bd..93b28ad 100644 (file)
--- 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);