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Commit 8ad7b378 authored by Davidlohr Bueso's avatar Davidlohr Bueso Committed by Ingo Molnar
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futex: Rename barrier references in ordering guarantees 



Ingo suggested we rename how we reference barriers A and B
regarding futex ordering guarantees. This patch replaces,
for both barriers, MB (A) with smp_mb(); (A), such that:

 - We explicitly state that the barriers are SMP, and

 - We standardize how we reference these across futex.c
   helping readers follow what barrier does what and where.

Suggested-by: default avatarIngo Molnar <mingo@kernel.org>
Signed-off-by: default avatarDavidlohr Bueso <dbueso@suse.de>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Chris Mason <clm@fb.com>
Cc: Darren Hart <dvhart@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: dave@stgolabs.net
Link: http://lkml.kernel.org/r/1455045314-8305-2-git-send-email-dave@stgolabs.net


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent e2d6f8a5

kernel/futex.c

+17 −17
Original line number Diff line number Diff line
@@ -124,7 +124,7 @@ 
 *   futex_wait(futex, val);

 *

 *   waiters++; (a)

 *   mb(); (A) <-- paired with -.

 *   smp_mb(); (A) <-- paired with -.

 *                                  |

 *   lock(hash_bucket(futex));      |

 *                                  |
@@ -133,7 +133,7 @@ 
 *                                  |        sys_futex(WAKE, futex);

 *                                  |          futex_wake(futex);

 *                                  |

 *                              `------->  mb(); (B)

 *                                  `--------> smp_mb(); (B)

 *   if (uval == val)

 *     queue();

 *     unlock(hash_bucket(futex));
@@ -334,7 +334,7 @@ static inline void futex_get_mm(union futex_key *key) 
	/*

	 * Ensure futex_get_mm() implies a full barrier such that

	 * get_futex_key() implies a full barrier. This is relied upon

	 * as full barrier (B), see the ordering comment above.

	 * as smp_mb(); (B), see the ordering comment above.

	 */

	smp_mb__after_atomic();

}
@@ -407,10 +407,10 @@ static void get_futex_key_refs(union futex_key *key) 


	switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {

	case FUT_OFF_INODE:

		ihold(key->shared.inode); /* implies MB (B) */

		ihold(key->shared.inode); /* implies smp_mb(); (B) */

		break;

	case FUT_OFF_MMSHARED:

		futex_get_mm(key); /* implies MB (B) */

		futex_get_mm(key); /* implies smp_mb(); (B) */

		break;

	default:

		/*
@@ -418,7 +418,7 @@ static void get_futex_key_refs(union futex_key *key) 
		 * mm, therefore the only purpose of calling get_futex_key_refs

		 * is because we need the barrier for the lockless waiter check.

		 */

		smp_mb(); /* explicit MB (B) */

		smp_mb(); /* explicit smp_mb(); (B) */

	}

}
@@ -497,7 +497,7 @@ get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw) 
	if (!fshared) {

		key->private.mm = mm;

		key->private.address = address;

		get_futex_key_refs(key);  /* implies MB (B) */

		get_futex_key_refs(key);  /* implies smp_mb(); (B) */

		return 0;

	}
@@ -572,7 +572,7 @@ get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw) 
		key->shared.pgoff = basepage_index(page);

	}



	get_futex_key_refs(key); /* implies MB (B) */

	get_futex_key_refs(key); /* implies smp_mb(); (B) */



out:

	unlock_page(page);
@@ -1864,7 +1864,7 @@ static inline struct futex_hash_bucket *queue_lock(struct futex_q *q) 


	q->lock_ptr = &hb->lock;



	spin_lock(&hb->lock); /* implies MB (A) */

	spin_lock(&hb->lock); /* implies smp_mb(); (A) */

	return hb;

}