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Subject[PATCH RT 14/25] futex: Split out the waiter check from lookup_pi_state()
3.2.68-rt99-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Thomas Gleixner <tglx@linutronix.de>

upstream commit: e60cbc5ceaa518d630ab8f35a7d05cee1c752648

We want to be a bit more clever in futex_lock_pi_atomic() and separate
the possible states. Split out the waiter verification into a separate
function. No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Darren Hart <darren@dvhart.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Davidlohr Bueso <davidlohr@hp.com>
Cc: Kees Cook <kees@outflux.net>
Cc: wad@chromium.org
Link: http://lkml.kernel.org/r/20140611204237.180458410@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
kernel/futex.c | 138 +++++++++++++++++++++++++++++----------------------------
1 file changed, 71 insertions(+), 67 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 73b91f7e7f61..58c66defd69b 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -643,92 +643,96 @@ void exit_pi_state_list(struct task_struct *curr)
* [10] There is no transient state which leaves owner and user space
* TID out of sync.
*/
-static int
-lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
- union futex_key *key, struct futex_pi_state **ps)
+
+/*
+ * Validate that the existing waiter has a pi_state and sanity check
+ * the pi_state against the user space value. If correct, attach to
+ * it.
+ */
+static int attach_to_pi_state(u32 uval, struct futex_pi_state *pi_state,
+ struct futex_pi_state **ps)
{
- struct futex_q *match = futex_top_waiter(hb, key);
- struct futex_pi_state *pi_state = NULL;
- struct task_struct *p;
pid_t pid = uval & FUTEX_TID_MASK;

- if (match) {
- /*
- * Sanity check the waiter before increasing the
- * refcount and attaching to it.
- */
- pi_state = match->pi_state;
- /*
- * Userspace might have messed up non-PI and PI
- * futexes [3]
- */
- if (unlikely(!pi_state))
- return -EINVAL;
+ /*
+ * Userspace might have messed up non-PI and PI futexes [3]
+ */
+ if (unlikely(!pi_state))
+ return -EINVAL;

- WARN_ON(!atomic_read(&pi_state->refcount));
+ WARN_ON(!atomic_read(&pi_state->refcount));

+ /*
+ * Handle the owner died case:
+ */
+ if (uval & FUTEX_OWNER_DIED) {
/*
- * Handle the owner died case:
+ * exit_pi_state_list sets owner to NULL and wakes the
+ * topmost waiter. The task which acquires the
+ * pi_state->rt_mutex will fixup owner.
*/
- if (uval & FUTEX_OWNER_DIED) {
- /*
- * exit_pi_state_list sets owner to NULL and
- * wakes the topmost waiter. The task which
- * acquires the pi_state->rt_mutex will fixup
- * owner.
- */
- if (!pi_state->owner) {
- /*
- * No pi state owner, but the user
- * space TID is not 0. Inconsistent
- * state. [5]
- */
- if (pid)
- return -EINVAL;
- /*
- * Take a ref on the state and
- * return. [4]
- */
- goto out_state;
- }
-
+ if (!pi_state->owner) {
/*
- * If TID is 0, then either the dying owner
- * has not yet executed exit_pi_state_list()
- * or some waiter acquired the rtmutex in the
- * pi state, but did not yet fixup the TID in
- * user space.
- *
- * Take a ref on the state and return. [6]
+ * No pi state owner, but the user space TID
+ * is not 0. Inconsistent state. [5]
*/
- if (!pid)
- goto out_state;
- } else {
+ if (pid)
+ return -EINVAL;
/*
- * If the owner died bit is not set,
- * then the pi_state must have an
- * owner. [7]
+ * Take a ref on the state and return success. [4]
*/
- if (!pi_state->owner)
- return -EINVAL;
+ goto out_state;
}

/*
- * Bail out if user space manipulated the
- * futex value. If pi state exists then the
- * owner TID must be the same as the user
- * space TID. [9/10]
+ * If TID is 0, then either the dying owner has not
+ * yet executed exit_pi_state_list() or some waiter
+ * acquired the rtmutex in the pi state, but did not
+ * yet fixup the TID in user space.
+ *
+ * Take a ref on the state and return success. [6]
+ */
+ if (!pid)
+ goto out_state;
+ } else {
+ /*
+ * If the owner died bit is not set, then the pi_state
+ * must have an owner. [7]
*/
- if (pid != task_pid_vnr(pi_state->owner))
+ if (!pi_state->owner)
return -EINVAL;
-
- out_state:
- atomic_inc(&pi_state->refcount);
- *ps = pi_state;
- return 0;
}

/*
+ * Bail out if user space manipulated the futex value. If pi
+ * state exists then the owner TID must be the same as the
+ * user space TID. [9/10]
+ */
+ if (pid != task_pid_vnr(pi_state->owner))
+ return -EINVAL;
+out_state:
+ atomic_inc(&pi_state->refcount);
+ *ps = pi_state;
+ return 0;
+}
+
+static int
+lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
+ union futex_key *key, struct futex_pi_state **ps)
+{
+ struct futex_q *match = futex_top_waiter(hb, key);
+ struct futex_pi_state *pi_state = NULL;
+ struct task_struct *p;
+ pid_t pid = uval & FUTEX_TID_MASK;
+
+ /*
+ * If there is a waiter on that futex, validate it and
+ * attach to the pi_state when the validation succeeds.
+ */
+ if (match)
+ return attach_to_pi_state(uval, match->pi_state, ps);
+
+ /*
* We are the first waiter - try to look up the real owner and attach
* the new pi_state to it, but bail out when TID = 0 [1]
*/
--
2.1.4



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