sched_ext: Move scx_error() out of scx_link_sched()'s lock region

scx_link_sched() holds scx_sched_lock. The scx_error() calls inside take the
same lock through scx_claim_exit() and deadlock. Move them out of the guard.

Fixes: 6b4576b09714 ("sched_ext: Reject sub-sched attachment to a disabled parent")
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 3f0d8aeaed819b0bb576477b0896aa4fcd0337ba..7d367c140a36be6923c899c7bff346e130c1ba0e 100644 (file)
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -5585,10 +5585,12 @@ static void refresh_watchdog(void)
 
 static s32 scx_link_sched(struct scx_sched *sch)
 {
+       const char *err_msg;
+       s32 ret = 0;
+
        scoped_guard(raw_spinlock_irq, &scx_sched_lock) {
 #ifdef CONFIG_EXT_SUB_SCHED
                struct scx_sched *parent = scx_parent(sch);
-               s32 ret;
 
                if (parent) {
                        /*
@@ -5598,15 +5600,16 @@ static s32 scx_link_sched(struct scx_sched *sch)
                         * parent can shoot us down.
                         */
                        if (atomic_read(&parent->exit_kind) != SCX_EXIT_NONE) {
-                               scx_error(sch, "parent disabled");
-                               return -ENOENT;
+                               err_msg = "parent disabled";
+                               ret = -ENOENT;
+                               break;
                        }
 
                        ret = rhashtable_lookup_insert_fast(&scx_sched_hash,
                                        &sch->hash_node, scx_sched_hash_params);
                        if (ret) {
-                               scx_error(sch, "failed to insert into scx_sched_hash (%d)", ret);
-                               return ret;
+                               err_msg = "failed to insert into scx_sched_hash";
+                               break;
                        }
 
                        list_add_tail(&sch->sibling, &parent->children);
@@ -5616,6 +5619,15 @@ static s32 scx_link_sched(struct scx_sched *sch)
                list_add_tail_rcu(&sch->all, &scx_sched_all);
        }
 
+       /*
+        * scx_error() takes scx_sched_lock via scx_claim_exit(), so it must run after
+        * the guard above is released.
+        */
+       if (ret) {
+               scx_error(sch, "%s (%d)", err_msg, ret);
+               return ret;
+       }
+
        refresh_watchdog();
        return 0;
 }