Commit 7e992711 authored by Dave Anglin's avatar Dave Anglin Committed by Helge Deller
Browse files

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: default avatarDave Anglin <dave.anglin@bell.net>
Signed-off-by: default avatarHelge Deller <deller@gmx.de>
parent 014966dc

arch/parisc/include/asm/futex.h

+11 −13
Original line number Diff line number Diff line
@@ -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;

}

arch/parisc/kernel/syscall.S

+0 −10
Original line number Diff line number Diff line
@@ -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 */