parisc: Don't disable interrupts in cmpxchg and futex operations

I no longer think interrupts can be disabled in the futex and cmpxchg operations because of COW breaks. This not ideal but I suspect it's the best we can do. For the cmpxchg operations in syscall.S, we rely on the code to not schedule off the gateway page. For the futex, I added code to disable preemption. So far, I haven't seen the warnings with the attached change but the change is only lightly tested. Signed-off-by: Dave Anglin <[email protected]> Signed-off-by: Helge Deller <[email protected]>
josf · Nov 4, 2021 · 7e99271 · 7e99271
1 parent 014966d
commit 7e99271
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Showing 2 changed files with 11 additions and 23 deletions.
diff --git a/arch/parisc/include/asm/futex.h b/arch/parisc/include/asm/futex.h
@@ -11,35 +11,34 @@
    sixteen four-word locks. */
 
 static inline void
-_futex_spin_lock_irqsave(u32 __user *uaddr, unsigned long int *flags)
+_futex_spin_lock(u32 __user *uaddr)
 {
 	extern u32 lws_lock_start[];
 	long index = ((long)uaddr & 0x3f8) >> 1;
 	arch_spinlock_t *s = (arch_spinlock_t *)&lws_lock_start[index];
-	local_irq_save(*flags);
+	preempt_disable();
 	arch_spin_lock(s);
 }
 
 static inline void
-_futex_spin_unlock_irqrestore(u32 __user *uaddr, unsigned long int *flags)
+_futex_spin_unlock(u32 __user *uaddr)
 {
 	extern u32 lws_lock_start[];
 	long index = ((long)uaddr & 0x3f8) >> 1;
 	arch_spinlock_t *s = (arch_spinlock_t *)&lws_lock_start[index];
 	arch_spin_unlock(s);
-	local_irq_restore(*flags);
+	preempt_enable();
 }
 
 static inline int
 arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
 {
-	unsigned long int flags;
 	int oldval, ret;
 	u32 tmp;
 
-	_futex_spin_lock_irqsave(uaddr, &flags);
-
 	ret = -EFAULT;
+
+	_futex_spin_lock(uaddr);
 	if (unlikely(get_user(oldval, uaddr) != 0))
 		goto out_pagefault_enable;
 
@@ -70,7 +69,7 @@ arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
 		ret = -EFAULT;
 
 out_pagefault_enable:
-	_futex_spin_unlock_irqrestore(uaddr, &flags);
+	_futex_spin_unlock(uaddr);
 
 	if (!ret)
 		*oval = oldval;
@@ -83,7 +82,6 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 			      u32 oldval, u32 newval)
 {
 	u32 val;
-	unsigned long flags;
 
 	/* futex.c wants to do a cmpxchg_inatomic on kernel NULL, which is
 	 * our gateway page, and causes no end of trouble...
@@ -100,19 +98,19 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 	 * address. This should scale to a couple of CPUs.
 	 */
 
-	_futex_spin_lock_irqsave(uaddr, &flags);
+	_futex_spin_lock(uaddr);
 	if (unlikely(get_user(val, uaddr) != 0)) {
-		_futex_spin_unlock_irqrestore(uaddr, &flags);
+		_futex_spin_unlock(uaddr);
 		return -EFAULT;
 	}
 
 	if (val == oldval && unlikely(put_user(newval, uaddr) != 0)) {
-		_futex_spin_unlock_irqrestore(uaddr, &flags);
+		_futex_spin_unlock(uaddr);
 		return -EFAULT;
 	}
 
 	*uval = val;
-	_futex_spin_unlock_irqrestore(uaddr, &flags);
+	_futex_spin_unlock(uaddr);
 
 	return 0;
 }

diff --git a/arch/parisc/kernel/syscall.S b/arch/parisc/kernel/syscall.S
@@ -597,13 +597,11 @@ cas_nocontend:
 # endif
 /* ENABLE_LWS_DEBUG */
 
-	rsm	PSW_SM_I, %r0				/* Disable interrupts */
 	/* COW breaks can cause contention on UP systems */
 	LDCW	0(%sr2,%r20), %r28			/* Try to acquire the lock */
 	cmpb,<>,n	%r0, %r28, cas_action		/* Did we get it? */
 cas_wouldblock:
 	ldo	2(%r0), %r28				/* 2nd case */
-	ssm	PSW_SM_I, %r0
 	b	lws_exit				/* Contended... */
 	ldo	-EAGAIN(%r0), %r21			/* Spin in userspace */
 
@@ -639,8 +637,6 @@ cas_action:
 	/* Clear thread register indicator */
 	stw	%r0, 4(%sr2,%r20)
 #endif
-	/* Enable interrupts */
-	ssm	PSW_SM_I, %r0
 	/* Return to userspace, set no error */
 	b	lws_exit
 	copy	%r0, %r21
@@ -652,7 +648,6 @@ cas_action:
 #if ENABLE_LWS_DEBUG
 	stw	%r0, 4(%sr2,%r20)
 #endif
-	ssm	PSW_SM_I, %r0
 	b	lws_exit
 	ldo	-EFAULT(%r0),%r21	/* set errno */
 	nop
@@ -764,13 +759,11 @@ cas2_lock_start:
 	shlw	%r20, 4, %r20
 	add	%r20, %r28, %r20
 
-	rsm	PSW_SM_I, %r0			/* Disable interrupts */
 	/* COW breaks can cause contention on UP systems */
 	LDCW	0(%sr2,%r20), %r28		/* Try to acquire the lock */
 	cmpb,<>,n	%r0, %r28, cas2_action	/* Did we get it? */
 cas2_wouldblock:
 	ldo	2(%r0), %r28			/* 2nd case */
-	ssm	PSW_SM_I, %r0
 	b	lws_exit			/* Contended... */
 	ldo	-EAGAIN(%r0), %r21		/* Spin in userspace */
 
@@ -850,8 +843,6 @@ cas2_action:
 cas2_end:
 	/* Free lock */
 	stw,ma	%r20, 0(%sr2,%r20)
-	/* Enable interrupts */
-	ssm	PSW_SM_I, %r0
 	/* Return to userspace, set no error */
 	b	lws_exit
 	copy	%r0, %r21
@@ -860,7 +851,6 @@ cas2_end:
 	/* Error occurred on load or store */
 	/* Free lock */
 	stw,ma	%r20, 0(%sr2,%r20)
-	ssm	PSW_SM_I, %r0
 	ldo	1(%r0),%r28
 	b	lws_exit
 	ldo	-EFAULT(%r0),%r21	/* set errno */