linux-kernel - [PATCH v4 05/20] futex: Add a new futex type field into futex

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Date:   Thu, 29 Dec 2016 11:13:31 -0500
From:   Waiman Long <longman@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jonathan Corbet <corbet@....net>
Cc:     linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Mike Galbraith <umgwanakikbuti@...il.com>,
        Scott J Norton <scott.norton@....com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH v4 05/20] futex: Add a new futex type field into futex_state

As the futex_state structure will be overloaded in later patches
to be used by non-PI futexes, it is necessary to add a type field to
distinguish among different types of futexes.

Signed-off-by: Waiman Long <longman@...hat.com>
---
 kernel/futex.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index ccec962..c8ff773 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -191,6 +191,10 @@
 #define FLAGS_CLOCKRT		0x02
 #define FLAGS_HAS_TIMEOUT	0x04
 
+enum futex_type {
+	TYPE_PI = 0,
+};
+
 /*
  * Futex state object:
  *  - Priority Inheritance state
@@ -210,6 +214,7 @@ struct futex_state {
 	struct task_struct *owner;
 	atomic_t refcount;
 
+	enum futex_type type;
 	union futex_key key;
 };
 
@@ -903,13 +908,14 @@ static void put_futex_state(struct futex_state *state)
 		return;
 
 	/*
-	 * If state->owner is NULL, the owner is most probably dying
-	 * and has cleaned up the futex state already
+	 * If state->owner is NULL and the type is TYPE_PI, the owner is
+	 * most probably dying and has cleaned up the futex state already.
 	 */
 	if (state->owner) {
 		task_pi_list_del(state, false);
 
-		rt_mutex_proxy_unlock(&state->pi_mutex, state->owner);
+		if (state->type == TYPE_PI)
+			rt_mutex_proxy_unlock(&state->pi_mutex, state->owner);
 	}
 
 	if (current->pi_state_cache)
@@ -1062,7 +1068,7 @@ static int attach_to_pi_state(u32 uval, struct futex_state *pi_state,
 	/*
 	 * Userspace might have messed up non-PI and PI futexes [3]
 	 */
-	if (unlikely(!pi_state))
+	if (unlikely(!pi_state || (pi_state->type != TYPE_PI)))
 		return -EINVAL;
 
 	WARN_ON(!atomic_read(&pi_state->refcount));
@@ -1180,6 +1186,7 @@ static int attach_to_pi_owner(u32 uval, union futex_key *key,
 
 	/* Store the key for possible exit cleanups: */
 	pi_state->key = *key;
+	pi_state->type = TYPE_PI;
 
 	WARN_ON(!list_empty(&pi_state->list));
 	list_add(&pi_state->list, &p->pi_state_list);
-- 
1.8.3.1