db7e007fd6
When using systemtap it was observed that our udelay implementation is rather suboptimal if being called from a kprobe handler installed by systemtap. The problem observed when a kprobe was installed on lock_acquired(). When the probe was hit the kprobe handler did call udelay, which set up an (internal) timer and reenabled interrupts (only the clock comparator interrupt) and waited for the interrupt. This is an optimization to avoid that the cpu is busy looping while waiting that enough time passes. The problem is that the interrupt handler still does call irq_enter()/irq_exit() which then again can lead to a deadlock, since some accounting functions may take locks as well. If one of these locks is the same, which caused lock_acquired() to be called, we have a nice deadlock. This patch reworks the udelay code for the interrupts disabled case to immediately leave the low level interrupt handler when the clock comparator interrupt happens. That way no C code is being called and the deadlock cannot happen anymore. Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Reviewed-by: Martin Schwidefsky <schwidefsky@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
129 lines
3.0 KiB
C
129 lines
3.0 KiB
C
/*
|
|
* Precise Delay Loops for S390
|
|
*
|
|
* Copyright IBM Corp. 1999, 2008
|
|
* Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>,
|
|
* Heiko Carstens <heiko.carstens@de.ibm.com>,
|
|
*/
|
|
|
|
#include <linux/sched.h>
|
|
#include <linux/delay.h>
|
|
#include <linux/timex.h>
|
|
#include <linux/module.h>
|
|
#include <linux/irqflags.h>
|
|
#include <linux/interrupt.h>
|
|
#include <linux/irq.h>
|
|
#include <asm/vtimer.h>
|
|
#include <asm/div64.h>
|
|
#include <asm/idle.h>
|
|
|
|
void __delay(unsigned long loops)
|
|
{
|
|
/*
|
|
* To end the bloody studid and useless discussion about the
|
|
* BogoMips number I took the liberty to define the __delay
|
|
* function in a way that that resulting BogoMips number will
|
|
* yield the megahertz number of the cpu. The important function
|
|
* is udelay and that is done using the tod clock. -- martin.
|
|
*/
|
|
asm volatile("0: brct %0,0b" : : "d" ((loops/2) + 1));
|
|
}
|
|
EXPORT_SYMBOL(__delay);
|
|
|
|
static void __udelay_disabled(unsigned long long usecs)
|
|
{
|
|
unsigned long cr0, cr0_new, psw_mask;
|
|
struct s390_idle_data idle;
|
|
u64 end;
|
|
|
|
end = get_tod_clock() + (usecs << 12);
|
|
__ctl_store(cr0, 0, 0);
|
|
cr0_new = cr0 & ~CR0_IRQ_SUBCLASS_MASK;
|
|
cr0_new |= (1UL << (63 - 52)); /* enable clock comparator irq */
|
|
__ctl_load(cr0_new, 0, 0);
|
|
psw_mask = __extract_psw() | PSW_MASK_EXT | PSW_MASK_WAIT;
|
|
set_clock_comparator(end);
|
|
set_cpu_flag(CIF_IGNORE_IRQ);
|
|
psw_idle(&idle, psw_mask);
|
|
clear_cpu_flag(CIF_IGNORE_IRQ);
|
|
set_clock_comparator(S390_lowcore.clock_comparator);
|
|
__ctl_load(cr0, 0, 0);
|
|
}
|
|
|
|
static void __udelay_enabled(unsigned long long usecs)
|
|
{
|
|
u64 clock_saved, end;
|
|
|
|
end = get_tod_clock_fast() + (usecs << 12);
|
|
do {
|
|
clock_saved = 0;
|
|
if (end < S390_lowcore.clock_comparator) {
|
|
clock_saved = local_tick_disable();
|
|
set_clock_comparator(end);
|
|
}
|
|
enabled_wait();
|
|
if (clock_saved)
|
|
local_tick_enable(clock_saved);
|
|
} while (get_tod_clock_fast() < end);
|
|
}
|
|
|
|
/*
|
|
* Waits for 'usecs' microseconds using the TOD clock comparator.
|
|
*/
|
|
void __udelay(unsigned long long usecs)
|
|
{
|
|
unsigned long flags;
|
|
|
|
preempt_disable();
|
|
local_irq_save(flags);
|
|
if (in_irq()) {
|
|
__udelay_disabled(usecs);
|
|
goto out;
|
|
}
|
|
if (in_softirq()) {
|
|
if (raw_irqs_disabled_flags(flags))
|
|
__udelay_disabled(usecs);
|
|
else
|
|
__udelay_enabled(usecs);
|
|
goto out;
|
|
}
|
|
if (raw_irqs_disabled_flags(flags)) {
|
|
local_bh_disable();
|
|
__udelay_disabled(usecs);
|
|
_local_bh_enable();
|
|
goto out;
|
|
}
|
|
__udelay_enabled(usecs);
|
|
out:
|
|
local_irq_restore(flags);
|
|
preempt_enable();
|
|
}
|
|
EXPORT_SYMBOL(__udelay);
|
|
|
|
/*
|
|
* Simple udelay variant. To be used on startup and reboot
|
|
* when the interrupt handler isn't working.
|
|
*/
|
|
void udelay_simple(unsigned long long usecs)
|
|
{
|
|
u64 end;
|
|
|
|
end = get_tod_clock_fast() + (usecs << 12);
|
|
while (get_tod_clock_fast() < end)
|
|
cpu_relax();
|
|
}
|
|
|
|
void __ndelay(unsigned long long nsecs)
|
|
{
|
|
u64 end;
|
|
|
|
nsecs <<= 9;
|
|
do_div(nsecs, 125);
|
|
end = get_tod_clock_fast() + nsecs;
|
|
if (nsecs & ~0xfffUL)
|
|
__udelay(nsecs >> 12);
|
|
while (get_tod_clock_fast() < end)
|
|
barrier();
|
|
}
|
|
EXPORT_SYMBOL(__ndelay);
|