linux-kernel - [PATCH 1/2] futex: Enhance comments in futex_lock

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Date:	Mon, 29 Jun 2015 23:26:01 -0700
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Darren Hart <darren@...art.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH 1/2] futex: Enhance comments in futex_lock_pi() for blocking paths

... serves a bit better to clarify between blocking
and non-blocking code paths.

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
 kernel/futex.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index c4a182f..153eb22 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2268,8 +2268,11 @@ static long futex_wait_restart(struct restart_block *restart)
 /*
  * Userspace tried a 0 -> TID atomic transition of the futex value
  * and failed. The kernel side here does the whole locking operation:
- * if there are waiters then it will block, it does PI, etc. (Due to
- * races the kernel might see a 0 value of the futex too.)
+ * if there are waiters then it will block as a consequence of relying
+ * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
+ * a 0 value of the futex too.).
+ *
+ * Also serves as futex trylock_pi()'ing, and due semantics.
  */
 static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
 			 ktime_t *time, int trylock)
@@ -2300,6 +2303,10 @@ retry_private:
 
 	ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
 	if (unlikely(ret)) {
+		/*
+		 * Atomic work succeeded and we got the lock,
+		 * or failed. Either way, we do _not_ block.
+		 */
 		switch (ret) {
 		case 1:
 			/* We got the lock. */
-- 
2.1.4

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