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Commit cc6db4e6 authored by Darren Hart's avatar Darren Hart Committed by Ingo Molnar
Browse files

futex: Correct futex_wait_requeue_pi() commentary 



The state machine described in the comments wasn't updated with
a follow-on fix.  Address that and cleanup the corresponding
commentary in the function.

Signed-off-by: default avatarDarren Hart <dvhltc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <4A737C2A.9090001@us.ibm.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent a33a052f

kernel/futex.c

+10 −13
Original line number Original line Diff line number Diff line
@@ -2102,11 +2102,11 @@ int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb, 
 * We call schedule in futex_wait_queue_me() when we enqueue and return there

 * We call schedule in futex_wait_queue_me() when we enqueue and return there

 * via the following:

 * via the following:

 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()

 * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()

 * 2) wakeup on uaddr2 after a requeue and subsequent unlock

 * 2) wakeup on uaddr2 after a requeue

 * 3) signal (before or after requeue)

 * 3) signal

 * 4) timeout (before or after requeue)

 * 4) timeout

 *

 *

 * If 3, we setup a restart_block with futex_wait_requeue_pi() as the function.

 * If 3, cleanup and return -ERESTARTNOINTR.

 *

 *

 * If 2, we may then block on trying to take the rt_mutex and return via:

 * If 2, we may then block on trying to take the rt_mutex and return via:

 * 5) successful lock

 * 5) successful lock
@@ -2114,7 +2114,7 @@ int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb, 
 * 7) timeout

 * 7) timeout

 * 8) other lock acquisition failure

 * 8) other lock acquisition failure

 *

 *

 * If 6, we setup a restart_block with futex_lock_pi() as the function.

 * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).

 *

 *

 * If 4 or 7, we cleanup and return with -ETIMEDOUT.

 * If 4 or 7, we cleanup and return with -ETIMEDOUT.

 *

 *
@@ -2232,14 +2232,11 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared, 
			rt_mutex_unlock(pi_mutex);

			rt_mutex_unlock(pi_mutex);

	} else if (ret == -EINTR) {

	} else if (ret == -EINTR) {

		/*

		/*

		 * We've already been requeued, but we have no way to

		 * We've already been requeued, but cannot restart by calling

		 * restart by calling futex_lock_pi() directly. We

		 * futex_lock_pi() directly. We could restart this syscall, but

		 * could restart the syscall, but that will look at

		 * it would detect that the user space "val" changed and return

		 * the user space value and return right away. So we

		 * -EWOULDBLOCK.  Save the overhead of the restart and return

		 * drop back with EWOULDBLOCK to tell user space that

		 * -EWOULDBLOCK directly.

		 * "val" has been changed. That's the same what the

		 * restart of the syscall would do in

		 * futex_wait_setup().

		 */

		 */

		ret = -EWOULDBLOCK;

		ret = -EWOULDBLOCK;

	}

	}