mm/damon: simplify stop mechanism

A kernel thread can exit gracefully with kthread_stop().  So we don't
need a new flag 'kdamond_stop'.  And to make sure the task struct is not
freed when accessing it, get reference to it before termination.

Link: https://lkml.kernel.org/r/20211027130517.4404-1-changbin.du@gmail.com
Signed-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>

diff --git a/include/linux/damon.h b/include/linux/damon.h
index fa7f32614b65e422bbaf2d66b272e923fdf55dc4..321de9d723600a38999ff617d66b5240bfb5b313 100644 (file)
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -381,7 +381,6 @@ struct damon_ctx {
 
 /* public: */
        struct task_struct *kdamond;
-       bool kdamond_stop;
        struct mutex kdamond_lock;
 
        struct damon_primitive primitive;

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 46a6afea3030cd7ed98ac72ce84b4bb303c6f258..f37c17b53814869c32fc906a6f449ae8d4029db1 100644 (file)
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -390,17 +390,6 @@ static unsigned long damon_region_sz_limit(struct damon_ctx *ctx)
        return sz;
 }
 
-static bool damon_kdamond_running(struct damon_ctx *ctx)
-{
-       bool running;
-
-       mutex_lock(&ctx->kdamond_lock);
-       running = ctx->kdamond != NULL;
-       mutex_unlock(&ctx->kdamond_lock);
-
-       return running;
-}
-
 static int kdamond_fn(void *data);
 
 /*
@@ -418,7 +407,6 @@ static int __damon_start(struct damon_ctx *ctx)
        mutex_lock(&ctx->kdamond_lock);
        if (!ctx->kdamond) {
                err = 0;
-               ctx->kdamond_stop = false;
                ctx->kdamond = kthread_run(kdamond_fn, ctx, "kdamond.%d",
                                nr_running_ctxs);
                if (IS_ERR(ctx->kdamond)) {
@@ -474,13 +462,15 @@ int damon_start(struct damon_ctx **ctxs, int nr_ctxs)
  */
 static int __damon_stop(struct damon_ctx *ctx)
 {
+       struct task_struct *tsk;
+
        mutex_lock(&ctx->kdamond_lock);
-       if (ctx->kdamond) {
-               ctx->kdamond_stop = true;
+       tsk = ctx->kdamond;
+       if (tsk) {
+               get_task_struct(tsk);
                mutex_unlock(&ctx->kdamond_lock);
-               while (damon_kdamond_running(ctx))
-                       usleep_range(ctx->sample_interval,
-                                       ctx->sample_interval * 2);
+               kthread_stop(tsk);
+               put_task_struct(tsk);
                return 0;
        }
        mutex_unlock(&ctx->kdamond_lock);
@@ -925,12 +915,8 @@ static bool kdamond_need_update_primitive(struct damon_ctx *ctx)
 static bool kdamond_need_stop(struct damon_ctx *ctx)
 {
        struct damon_target *t;
-       bool stop;
 
-       mutex_lock(&ctx->kdamond_lock);
-       stop = ctx->kdamond_stop;
-       mutex_unlock(&ctx->kdamond_lock);
-       if (stop)
+       if (kthread_should_stop())
                return true;
 
        if (!ctx->primitive.target_valid)
@@ -1021,13 +1007,6 @@ static int kdamond_wait_activation(struct damon_ctx *ctx)
        return -EBUSY;
 }
 
-static void set_kdamond_stop(struct damon_ctx *ctx)
-{
-       mutex_lock(&ctx->kdamond_lock);
-       ctx->kdamond_stop = true;
-       mutex_unlock(&ctx->kdamond_lock);
-}
-
 /*
  * The monitoring daemon that runs as a kernel thread
  */
@@ -1038,17 +1017,18 @@ static int kdamond_fn(void *data)
        struct damon_region *r, *next;
        unsigned int max_nr_accesses = 0;
        unsigned long sz_limit = 0;
+       bool done = false;
 
        pr_debug("kdamond (%d) starts\n", current->pid);
 
        if (ctx->primitive.init)
                ctx->primitive.init(ctx);
        if (ctx->callback.before_start && ctx->callback.before_start(ctx))
-               set_kdamond_stop(ctx);
+               done = true;
 
        sz_limit = damon_region_sz_limit(ctx);
 
-       while (!kdamond_need_stop(ctx)) {
+       while (!kdamond_need_stop(ctx) && !done) {
                if (kdamond_wait_activation(ctx))
                        continue;
 
@@ -1056,7 +1036,7 @@ static int kdamond_fn(void *data)
                        ctx->primitive.prepare_access_checks(ctx);
                if (ctx->callback.after_sampling &&
                                ctx->callback.after_sampling(ctx))
-                       set_kdamond_stop(ctx);
+                       done = true;
 
                usleep_range(ctx->sample_interval, ctx->sample_interval + 1);
 
@@ -1069,7 +1049,7 @@ static int kdamond_fn(void *data)
                                        sz_limit);
                        if (ctx->callback.after_aggregation &&
                                        ctx->callback.after_aggregation(ctx))
-                               set_kdamond_stop(ctx);
+                               done = true;
                        kdamond_apply_schemes(ctx);
                        kdamond_reset_aggregated(ctx);
                        kdamond_split_regions(ctx);
@@ -1088,9 +1068,8 @@ static int kdamond_fn(void *data)
                        damon_destroy_region(r, t);
        }
 
-       if (ctx->callback.before_terminate &&
-                       ctx->callback.before_terminate(ctx))
-               set_kdamond_stop(ctx);
+       if (ctx->callback.before_terminate)
+               ctx->callback.before_terminate(ctx);
        if (ctx->primitive.cleanup)
                ctx->primitive.cleanup(ctx);