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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: Darren 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: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Darren Hart 2009-07-31 16:20:10 -07:00 committed by Ingo Molnar
parent a33a052f19
commit cc6db4e601
1 changed files with 10 additions and 13 deletions
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23
kernel/futex.c
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@ -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
* via the following:
* 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
* 2) wakeup on uaddr2 after a requeue and subsequent unlock
* 3) signal (before or after requeue)
* 4) timeout (before or after requeue)
* 2) wakeup on uaddr2 after a requeue
* 3) signal
* 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:
* 5) successful lock
@ -2114,7 +2114,7 @@ int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
* 7) timeout
* 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.
*
@ -2232,14 +2232,11 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared,
rt_mutex_unlock(pi_mutex);
} else if (ret == -EINTR) {
/*
* We've already been requeued, but we have no way to
* restart by calling futex_lock_pi() directly. We
* could restart the syscall, but that will look at
* the user space value and return right away. So we
* drop back with EWOULDBLOCK to tell user space that
* "val" has been changed. That's the same what the
* restart of the syscall would do in
* futex_wait_setup().
* We've already been requeued, but cannot restart by calling
* futex_lock_pi() directly. We could restart this syscall, but
* it would detect that the user space "val" changed and return
* -EWOULDBLOCK. Save the overhead of the restart and return
* -EWOULDBLOCK directly.
*/
ret = -EWOULDBLOCK;
}