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Subject[tip:locking/core] futex: Split out the first waiter attachment from lookup_pi_state()
Commit-ID:  04e1b2e52b17195c9a1daa5935c55a4c8716095c
Gitweb: http://git.kernel.org/tip/04e1b2e52b17195c9a1daa5935c55a4c8716095c
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Wed, 11 Jun 2014 20:45:40 +0000
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Sat, 21 Jun 2014 22:26:23 +0200

futex: Split out the first waiter attachment from lookup_pi_state()

We want to be a bit more clever in futex_lock_pi_atomic() and separate
the possible states. Split out the code which attaches the first
waiter to the owner 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/20140611204237.271300614@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/futex.c | 42 ++++++++++++++++++++++++++++--------------
1 file changed, 28 insertions(+), 14 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index db0c686..e65b686 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -865,21 +865,16 @@ out_state:
return 0;
}

-static int
-lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
- union futex_key *key, struct futex_pi_state **ps)
+/*
+ * Lookup the task for the TID provided from user space and attach to
+ * it after doing proper sanity checks.
+ */
+static int attach_to_pi_owner(u32 uval, 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);
+ struct futex_pi_state *pi_state;
+ struct task_struct *p;

/*
* We are the first waiter - try to look up the real owner and attach
@@ -922,7 +917,7 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
pi_state = alloc_pi_state();

/*
- * Initialize the pi_mutex in locked state and make 'p'
+ * Initialize the pi_mutex in locked state and make @p
* the owner of it:
*/
rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
@@ -942,6 +937,25 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
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);
+
+ /*
+ * 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 owner based on
+ * @uval and attach to it.
+ */
+ return attach_to_pi_owner(uval, key, ps);
+}
+
/**
* futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
* @uaddr: the pi futex user address

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