mm/damon: needn't hold kdamond_lock to print pid of kdamond

Just get the pid by 'current->pid'.  Meanwhile, to be symmetrical make
the 'starts' and 'finishes' logs both use debug level.

Link: https://lkml.kernel.org/r/20210927232432.17750-1-changbin.du@gmail.comSigned-off-by: Changbin Du <changbin.du@gmail.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/damon/core.c

@@ -652,9 +652,7 @@ static int kdamond_fn(void *data)
 	unsigned int max_nr_accesses = 0;
 	unsigned long sz_limit = 0;
 
-	mutex_lock(&ctx->kdamond_lock);
-	pr_debug("kdamond (%d) starts\n", ctx->kdamond->pid);
-	mutex_unlock(&ctx->kdamond_lock);
+	pr_debug("kdamond (%d) starts\n", current->pid);
 
 	if (ctx->primitive.init)
 		ctx->primitive.init(ctx);
@@ -705,7 +703,7 @@ static int kdamond_fn(void *data)
 	if (ctx->primitive.cleanup)
 		ctx->primitive.cleanup(ctx);
 
-	pr_debug("kdamond (%d) finishes\n", ctx->kdamond->pid);
+	pr_debug("kdamond (%d) finishes\n", current->pid);
 	mutex_lock(&ctx->kdamond_lock);
 	ctx->kdamond = NULL;
 	mutex_unlock(&ctx->kdamond_lock);