futex: Mention key referencing differences between shared and private futexes (993b2ff2) · Commits · 戴 / test

Update our documentation as of fix (futex: Ensure get_futex_key_refs() always implies a barrier). Explicitly state that we don't do key referencing for private futexes. Signed-off-by:

Davidlohr Bueso <dbueso@suse.de> Cc: Matteo Franchin <Matteo.Franchin@arm.com> Cc: Davidlohr Bueso <davidlohr@hp.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Darren Hart <dvhart@linux.intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by:

Catalin Marinas <catalin.marinas@arm.com> Link: http://lkml.kernel.org/r/1414121220.817.0.camel@linux-t7sj.site Signed-off-by:

Thomas Gleixner <tglx@linutronix.de>

kernel/futex.c

+10 −4

Original line number	Diff line number	Diff line
		@@ -143,9 +143,8 @@
		*
		* Where (A) orders the waiters increment and the futex value read through
		* atomic operations (see hb_waiters_inc) and where (B) orders the write
		* to futex and the waiters read -- this is done by the barriers in
		* get_futex_key_refs(), through either ihold or atomic_inc, depending on the
		* futex type.
		* to futex and the waiters read -- this is done by the barriers for both
		* shared and private futexes in get_futex_key_refs().
		*
		* This yields the following case (where X:=waiters, Y:=futex):
		*
		@@ -344,13 +343,20 @@ static void get_futex_key_refs(union futex_key *key)
		futex_get_mm(key); /* implies MB (B) */
		break;
		default:
		/*
		* Private futexes do not hold reference on an inode or
		* 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) */
		}
		}

		/*
		* Drop a reference to the resource addressed by a key.
		* The hash bucket spinlock must not be held.
		* The hash bucket spinlock must not be held. This is
		* a no-op for private futexes, see comment in the get
		* counterpart.
		*/
		static void drop_futex_key_refs(union futex_key *key)
		{

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