linux-kernel - [PATCH v3 05/13] futex: Add a new futex type field into futex

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Date:   Fri, 30 Sep 2016 17:26:14 -0400
From:   Waiman Long <Waiman.Long@....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>,
        Jason Low <jason.low2@....com>,
        Scott J Norton <scott.norton@....com>,
        Douglas Hatch <doug.hatch@....com>,
        Waiman Long <Waiman.Long@....com>
Subject: [PATCH v3 05/13] 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 <Waiman.Long@....com>
---
 kernel/futex.c |   14 ++++++++++----
 1 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 0d1b1be..a496c01 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -191,6 +191,10 @@ int __read_mostly futex_cmpxchg_enabled;
 #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;
 };
 
@@ -897,10 +902,10 @@ 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) {
+	if (state->owner && (state->type == TYPE_PI)) {
 		task_pi_list_del(state->owner, state, false);
 
 		rt_mutex_proxy_unlock(&state->pi_mutex, state->owner);
@@ -1056,7 +1061,7 @@ 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));
@@ -1174,6 +1179,7 @@ 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);
-- 
1.7.1