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[POWERPC] Make soft_enabled irqs preempt safe

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Rewrite local_get_flags and local_irq_disable to use r13 explicitly,
to avoid the risk that gcc will split get_paca()->soft_enabled into a
sequence unsafe against preemption.  Similar care in local_irq_restore.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
This commit is contained in:
Hugh Dickins 2006-11-10 21:32:40 +00:00 committed by Paul Mackerras
parent 56291e19e3
commit ef2b343e99
2 changed files with 67 additions and 10 deletions
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57
arch/powerpc/kernel/irq.c
View file

@ -97,22 +97,69 @@ EXPORT_SYMBOL(irq_desc);
int distribute_irqs = 1;
static inline unsigned long get_hard_enabled(void)
{
unsigned long enabled;
__asm__ __volatile__("lbz %0,%1(13)"
: "=r" (enabled) : "i" (offsetof(struct paca_struct, hard_enabled)));
return enabled;
}
static inline void set_soft_enabled(unsigned long enable)
{
__asm__ __volatile__("stb %0,%1(13)"
: : "r" (enable), "i" (offsetof(struct paca_struct, soft_enabled)));
}
void local_irq_restore(unsigned long en)
{
get_paca()->soft_enabled = en;
/*
* get_paca()->soft_enabled = en;
* Is it ever valid to use local_irq_restore(0) when soft_enabled is 1?
* That was allowed before, and in such a case we do need to take care
* that gcc will set soft_enabled directly via r13, not choose to use
* an intermediate register, lest we're preempted to a different cpu.
*/
set_soft_enabled(en);
if (!en)
return;
if (firmware_has_feature(FW_FEATURE_ISERIES)) {
if (get_paca()->lppaca_ptr->int_dword.any_int)
/*
* Do we need to disable preemption here? Not really: in the
* unlikely event that we're preempted to a different cpu in
* between getting r13, loading its lppaca_ptr, and loading
* its any_int, we might call iseries_handle_interrupts without
* an interrupt pending on the new cpu, but that's no disaster,
* is it? And the business of preempting us off the old cpu
* would itself involve a local_irq_restore which handles the
* interrupt to that cpu.
*
* But use "local_paca->lppaca_ptr" instead of "get_lppaca()"
* to avoid any preemption checking added into get_paca().
*/
if (local_paca->lppaca_ptr->int_dword.any_int)
iseries_handle_interrupts();
return;
}
if (get_paca()->hard_enabled)
/*
* if (get_paca()->hard_enabled) return;
* But again we need to take care that gcc gets hard_enabled directly
* via r13, not choose to use an intermediate register, lest we're
* preempted to a different cpu in between the two instructions.
*/
if (get_hard_enabled())
return;
/* need to hard-enable interrupts here */
get_paca()->hard_enabled = en;
/*
* Need to hard-enable interrupts here. Since currently disabled,
* no need to take further asm precautions against preemption; but
* use local_paca instead of get_paca() to avoid preemption checking.
*/
local_paca->hard_enabled = en;
if ((int)mfspr(SPRN_DEC) < 0)
mtspr(SPRN_DEC, 1);
hard_irq_enable();

20
include/asm-powerpc/hw_irq.h
View file

@ -18,15 +18,25 @@ extern void timer_interrupt(struct pt_regs *);
static inline unsigned long local_get_flags(void)
{
return get_paca()->soft_enabled;
unsigned long flags;
__asm__ __volatile__("lbz %0,%1(13)"
: "=r" (flags)
: "i" (offsetof(struct paca_struct, soft_enabled)));
return flags;
}
static inline unsigned long local_irq_disable(void)
{
unsigned long flag = get_paca()->soft_enabled;
get_paca()->soft_enabled = 0;
barrier();
return flag;
unsigned long flags, zero;
__asm__ __volatile__("li %1,0; lbz %0,%2(13); stb %1,%2(13)"
: "=r" (flags), "=&r" (zero)
: "i" (offsetof(struct paca_struct, soft_enabled))
: "memory");
return flags;
}
extern void local_irq_restore(unsigned long);