mm/damon/dbgfs: add adaptive_targets list check before enable monitor_on

When the ctx->adaptive_targets list is empty, I did some test on
monitor_on interface like this.

    # cat /sys/kernel/debug/damon/target_ids
    #
    # echo on > /sys/kernel/debug/damon/monitor_on
    # damon: kdamond (5390) starts

Though the ctx->adaptive_targets list is empty, but the kthread_run
still be called, and the kdamond.x thread still be created, this is
meaningless.

So there adds a judgment in 'dbgfs_monitor_on_write', if the
ctx->adaptive_targets list is empty, return -EINVAL.

Link: https://lkml.kernel.org/r/0a60a6e8ec9d71989e0848a4dc3311996ca3b5d4.1634720326.git.xhao@linux.alibaba.com
Signed-off-by: Xin Hao <xhao@linux.alibaba.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>

1 files changed, 12 insertions, 3 deletions

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index 6828e463348b..befb27a29aab 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -878,12 +878,21 @@ static ssize_t dbgfs_monitor_on_write(struct file *file,
 		return -EINVAL;
 	}
 
-	if (!strncmp(kbuf, "on", count))
+	if (!strncmp(kbuf, "on", count)) {
+		int i;
+
+		for (i = 0; i < dbgfs_nr_ctxs; i++) {
+			if (damon_targets_empty(dbgfs_ctxs[i])) {
+				kfree(kbuf);
+				return -EINVAL;
+			}
+		}
 		ret = damon_start(dbgfs_ctxs, dbgfs_nr_ctxs);
-	else if (!strncmp(kbuf, "off", count))
+	} else if (!strncmp(kbuf, "off", count)) {
 		ret = damon_stop(dbgfs_ctxs, dbgfs_nr_ctxs);
-	else
+	} else {
 		ret = -EINVAL;
+	}
 
 	if (!ret)
 		ret = count;