Helge
From 381599d3eb726623948c6b4adb2ea49a7359232b Mon Sep 17 00:00:00 2001
From: Dave Anglin <dave.anglin@xxxxxxxx>
Date: Wed, 3 Nov 2021 12:49:32 +0100
Subject: [PATCH] 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 <dave.anglin@xxxxxxxx>
Signed-off-by: Helge Deller <deller@xxxxxx>
diff --git a/arch/parisc/include/asm/futex.h b/arch/parisc/include/asm/futex.h
index fceb9cf02fb3..05fe92453b29 100644
--- a/arch/parisc/include/asm/futex.h
+++ b/arch/parisc/include/asm/futex.h
@@ -13,35 +13,34 @@
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;
@@ -72,7 +71,7 @@ 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;
@@ -85,7 +84,6 @@ 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...
@@ -102,19 +100,19 @@ 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
index 3f24a0af1e04..5b8feeeedf40 100644
--- a/arch/parisc/kernel/syscall.S
+++ b/arch/parisc/kernel/syscall.S
@@ -603,13 +603,11 @@ 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 */
@@ -645,8 +643,6 @@ 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
@@ -658,7 +654,6 @@ 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
@@ -770,13 +765,11 @@ 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 */
@@ -856,8 +849,6 @@ 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
@@ -866,7 +857,6 @@ 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 */
