[PATCH] sched-fix-scheduling-latencies-in-mttrc reenables interrupts

From: Bernard Blackham
Date: Mon Dec 27 2004 - 01:29:49 EST


Hi Ingo & Andrew,

The patch sched-fix-scheduling-latencies-in-mttr in recent -mm
kernels has the bad side-effect of re-enabling interrupts even if
they were disabled. This caused bugs in Software Suspend 2 which
reenabled MTRRs whilst interrupts were already disabled.

Attached is a replacement patch which uses spin_lock_irqsave instead
of spin_lock_irq.

Kind regards,

Bernard.

--
Bernard Blackham <bernard at blackham dot com dot au>
--- linux-2.6.10/arch/i386/kernel/cpu/mtrr/generic.c.orig 2004-10-19 05:54:32.000000000 +0800
+++ linux-2.6.10/arch/i386/kernel/cpu/mtrr/generic.c 2004-12-26 18:20:17.000000000 +0800
@@ -232,6 +232,7 @@ static unsigned long set_mtrr_state(u32
static unsigned long cr4 = 0;
static u32 deftype_lo, deftype_hi;
static spinlock_t set_atomicity_lock = SPIN_LOCK_UNLOCKED;
+static unsigned long sal_flags;

static void prepare_set(void)
{
@@ -240,11 +241,14 @@ static void prepare_set(void)
/* Note that this is not ideal, since the cache is only flushed/disabled
for this CPU while the MTRRs are changed, but changing this requires
more invasive changes to the way the kernel boots */
- spin_lock(&set_atomicity_lock);
+ /*
+ * Since we are disabling the cache dont allow any interrupts - they
+ * would run extremely slow and would only increase the pain:
+ */
+ spin_lock_irqsave(&set_atomicity_lock, sal_flags);

/* Enter the no-fill (CD=1, NW=0) cache mode and flush caches. */
cr0 = read_cr0() | 0x40000000; /* set CD flag */
- wbinvd();
write_cr0(cr0);
wbinvd();

@@ -266,8 +270,7 @@ static void prepare_set(void)

static void post_set(void)
{
- /* Flush caches and TLBs */
- wbinvd();
+ /* Flush TLBs (no need to flush caches - they are disabled) */
__flush_tlb();

/* Intel (P6) standard MTRRs */
@@ -279,7 +282,7 @@ static void post_set(void)
/* Restore value of CR4 */
if ( cpu_has_pge )
write_cr4(cr4);
- spin_unlock(&set_atomicity_lock);
+ spin_unlock_irqrestore(&set_atomicity_lock, sal_flags);
}

static void generic_set_all(void)