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[S390] nohz: Fix __udelay. 

This fixes a regression that came with 934b2857cc
("[S390] nohz/sclp: disable timer on synchronous waits.").
If udelay() gets called from a disabled context it sets the clock comparator
to a value where it expects the next interrupt. When the interrupt happens
the clock comparator gets not reset and therefore the interrupt condition
doesn't get cleared. The result is an endless timer interrupt loop.

In addition this patch fixes also the following:

rcutorture reveals that our __udelay implementation is still buggy,
since it might schedule tasklets, but prevents their execution:

NOHZ: local_softirq_pending 42
NOHZ: local_softirq_pending 02
NOHZ: local_softirq_pending 142
NOHZ: local_softirq_pending 02

To fix this we make sure that only the clock comparator interrupt
is enabled when the enabled wait psw is loaded.
Also no code gets called anymore which might schedule tasklets.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Heiko Carstens 2008-10-03 21:54:59 +02:00 committed by Martin Schwidefsky
parent 95b866d5af
commit d3d238c774
2 changed files with 59 additions and 37 deletions
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2
arch/s390/kernel/time.c
View File

@ -169,6 +169,8 @@ void init_cpu_timer(void)
static void clock_comparator_interrupt(__u16 code) static void clock_comparator_interrupt(__u16 code)
{ {
if (S390_lowcore.clock_comparator == -1ULL)
set_clock_comparator(S390_lowcore.clock_comparator);
} }
static void etr_timing_alert(struct etr_irq_parm *); static void etr_timing_alert(struct etr_irq_parm *);

94
arch/s390/lib/delay.c
View File

@ -1,14 +1,9 @@
/* /*
* arch/s390/lib/delay.c
* Precise Delay Loops for S390 * Precise Delay Loops for S390
* *
* S390 version * Copyright IBM Corp. 1999,2008
* Copyright (C) 1999 IBM Deutschland Entwicklung GmbH, IBM Corporation * Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>,
* Author(s): Martin Schwidefsky (schwidefsky@de.ibm.com), * Heiko Carstens <heiko.carstens@de.ibm.com>,
*
* Derived from "arch/i386/lib/delay.c"
* Copyright (C) 1993 Linus Torvalds
* Copyright (C) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
*/ */
#include <linux/sched.h> #include <linux/sched.h>
@ -29,30 +24,31 @@ void __delay(unsigned long loops)
asm volatile("0: brct %0,0b" : : "d" ((loops/2) + 1)); asm volatile("0: brct %0,0b" : : "d" ((loops/2) + 1));
} }
/* static void __udelay_disabled(unsigned long usecs)
* Waits for 'usecs' microseconds using the TOD clock comparator.
*/
void __udelay(unsigned long usecs)
{ {
u64 end, time, old_cc = 0; unsigned long mask, cr0, cr0_saved;
unsigned long flags, cr0, mask, dummy; u64 clock_saved;
int irq_context;
irq_context = in_interrupt(); clock_saved = local_tick_disable();
if (!irq_context) set_clock_comparator(get_clock() + ((u64) usecs << 12));
local_bh_disable(); __ctl_store(cr0_saved, 0, 0);
local_irq_save(flags); cr0 = (cr0_saved & 0xffff00e0) | 0x00000800;
if (raw_irqs_disabled_flags(flags)) { __ctl_load(cr0 , 0, 0);
old_cc = local_tick_disable(); mask = psw_kernel_bits | PSW_MASK_WAIT | PSW_MASK_EXT;
S390_lowcore.clock_comparator = -1ULL; trace_hardirqs_on();
__ctl_store(cr0, 0, 0); __load_psw_mask(mask);
dummy = (cr0 & 0xffff00e0) | 0x00000800; local_irq_disable();
__ctl_load(dummy , 0, 0); __ctl_load(cr0_saved, 0, 0);
mask = psw_kernel_bits | PSW_MASK_WAIT | PSW_MASK_EXT; local_tick_enable(clock_saved);
} else set_clock_comparator(S390_lowcore.clock_comparator);
mask = psw_kernel_bits | PSW_MASK_WAIT | }
PSW_MASK_EXT | PSW_MASK_IO;
static void __udelay_enabled(unsigned long usecs)
{
unsigned long mask;
u64 end, time;
mask = psw_kernel_bits | PSW_MASK_WAIT | PSW_MASK_EXT | PSW_MASK_IO;
end = get_clock() + ((u64) usecs << 12); end = get_clock() + ((u64) usecs << 12);
do { do {
time = end < S390_lowcore.clock_comparator ? time = end < S390_lowcore.clock_comparator ?
@ -62,13 +58,37 @@ void __udelay(unsigned long usecs)
__load_psw_mask(mask); __load_psw_mask(mask);
local_irq_disable(); local_irq_disable();
} while (get_clock() < end); } while (get_clock() < end);
if (raw_irqs_disabled_flags(flags)) {
__ctl_load(cr0, 0, 0);
local_tick_enable(old_cc);
}
if (!irq_context)
_local_bh_enable();
set_clock_comparator(S390_lowcore.clock_comparator); set_clock_comparator(S390_lowcore.clock_comparator);
local_irq_restore(flags); }
/*
* Waits for 'usecs' microseconds using the TOD clock comparator.
*/
void __udelay(unsigned 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();
} }