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>

diff --git a/include/linux/damon.h b/include/linux/damon.h
index c93325e..fa7f326 100644 (file)
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -440,6 +440,7 @@ void damon_destroy_scheme(struct damos *s);
 
 struct damon_target *damon_new_target(unsigned long id);
 void damon_add_target(struct damon_ctx *ctx, struct damon_target *t);
+bool damon_targets_empty(struct damon_ctx *ctx);
 void damon_free_target(struct damon_target *t);
 void damon_destroy_target(struct damon_target *t);
 unsigned int damon_nr_regions(struct damon_target *t);

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 6993c60..46a6afe 100644 (file)
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -180,6 +180,11 @@ void damon_add_target(struct damon_ctx *ctx, struct damon_target *t)
        list_add_tail(&t->list, &ctx->adaptive_targets);
 }
 
+bool damon_targets_empty(struct damon_ctx *ctx)
+{
+       return list_empty(&ctx->adaptive_targets);
+}
+
 static void damon_del_target(struct damon_target *t)
 {
        list_del(&t->list);

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index 6828e46..befb27a 100644 (file)
--- 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;