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Commit b5fa01a2 authored by Davidlohr Bueso's avatar Davidlohr Bueso Committed by Linus Torvalds
Browse files

ipc/sem: simplify wait-wake loop 

Instead of using the reverse goto, we can simplify the flow and make it
more language natural by just doing do-while instead.  One would hope
this is the standard way (or obviously just with a while bucle) that we
do wait/wakeup handling in the kernel.  The exact same logic is kept,
just more indented.

[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/1478708774-28826-2-git-send-email-dave@stgolabs.net


Signed-off-by: default avatarDavidlohr Bueso <dbueso@suse.de>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f150f02c

ipc/sem.c

+52 −56
Original line number Diff line number Diff line
@@ -1963,7 +1963,7 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops, 
		sma->complex_count++;

	}



sleep_again:

	do {

		queue.status = -EINTR;

		queue.sleeper = current;
@@ -1977,22 +1977,23 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops, 
			schedule();



		/*

	 * fastpath: the semop has completed, either successfully or not, from

	 * the syscall pov, is quite irrelevant to us at this point; we're done.

		 * fastpath: the semop has completed, either successfully or

		 * not, from the syscall pov, is quite irrelevant to us at this

		 * point; we're done.

		 *

		 * We _do_ care, nonetheless, about being awoken by a signal or

	 * spuriously.  The queue.status is checked again in the slowpath (aka

	 * after taking sem_lock), such that we can detect scenarios where we

	 * were awakened externally, during the window between wake_q_add() and

	 * wake_up_q().

		 * spuriously.  The queue.status is checked again in the

		 * slowpath (aka after taking sem_lock), such that we can detect

		 * scenarios where we were awakened externally, during the

		 * window between wake_q_add() and wake_up_q().

		 */

		error = READ_ONCE(queue.status);

		if (error != -EINTR) {

			/*

		 * User space could assume that semop() is a memory barrier:

		 * Without the mb(), the cpu could speculatively read in user

		 * space stale data that was overwritten by the previous owner

		 * of the semaphore.

			 * User space could assume that semop() is a memory

			 * barrier: Without the mb(), the cpu could

			 * speculatively read in userspace stale data that was

			 * overwritten by the previous owner of the semaphore.

			 */

			smp_mb();

			goto out_free;
@@ -2022,12 +2023,7 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops, 
		 */

		if (timeout && jiffies_left == 0)

			error = -EAGAIN;



	/*

	 * If the wakeup was spurious, just retry.

	 */

	if (error == -EINTR && !signal_pending(current))

		goto sleep_again;

	} while (error == -EINTR && !signal_pending(current)); /* spurious */



	unlink_queue(sma, &queue);