linux-kernel - [PATCH RT 15/19] Revert "futex: workaround migrate

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Date:   Thu,  8 Aug 2019 14:52:43 -0500
From:   zanussi@...nel.org
To:     LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Carsten Emde <C.Emde@...dl.org>,
        John Kacur <jkacur@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Daniel Wagner <wagi@...om.org>,
        Tom Zanussi <zanussi@...nel.org>,
        Julia Cartwright <julia@...com>
Subject: [PATCH RT 15/19] Revert "futex: workaround migrate_disable/enable in different context"

From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

v4.14.137-rt65-rc1 stable review patch.
If anyone has any objections, please let me know.

-----------


[ Upstream commit a71221d81cc4873891ae44f3aa02df596079b786 ]

Drop the RT fixup, the futex code will be changed to avoid the need for
the workaround.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Tom Zanussi <zanussi@...nel.org>

 Conflicts:
	kernel/futex.c
---
 kernel/futex.c | 19 -------------------
 1 file changed, 19 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index cb7e212fba0f..ec90130cd809 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2893,14 +2893,6 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
 	 * before __rt_mutex_start_proxy_lock() is done.
 	 */
 	raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
-	/*
-	 * the migrate_disable() here disables migration in the in_atomic() fast
-	 * path which is enabled again in the following spin_unlock(). We have
-	 * one migrate_disable() pending in the slow-path which is reversed
-	 * after the raw_spin_unlock_irq() where we leave the atomic context.
-	 */
-	migrate_disable();
-
 	spin_unlock(q.lock_ptr);
 	/*
 	 * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter
@@ -2909,7 +2901,6 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
 	 */
 	ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
 	raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
-	migrate_enable();
 
 	if (ret) {
 		if (ret == 1)
@@ -3058,21 +3049,11 @@ static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
 		 * rt_waiter. Also see the WARN in wake_futex_pi().
 		 */
 		raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
-		/*
-		 * Magic trickery for now to make the RT migrate disable
-		 * logic happy. The following spin_unlock() happens with
-		 * interrupts disabled so the internal migrate_enable()
-		 * won't undo the migrate_disable() which was issued when
-		 * locking hb->lock.
-		 */
-		migrate_disable();
 		spin_unlock(&hb->lock);
 
 		/* drops pi_state->pi_mutex.wait_lock */
 		ret = wake_futex_pi(uaddr, uval, pi_state);
 
-		migrate_enable();
-
 		put_pi_state(pi_state);
 
 		/*
-- 
2.14.1