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authorHeiko Carstens <heiko.carstens@de.ibm.com>2015-08-15 11:42:21 +0200
committerMartin Schwidefsky <schwidefsky@de.ibm.com>2015-10-14 14:32:13 +0200
commitdb7e007fd61ca07e5f3b04cf2168531b074d318d (patch)
tree998423a5b6cfdc90b2ce91c271fa3ba0ffc380f7 /arch/s390/lib
parent0c5a69f432ba1e586ac6ae5e4311c2f1cbd051fa (diff)
downloadlinux-linaro-stable-db7e007fd61ca07e5f3b04cf2168531b074d318d.tar.gz
s390/udelay: make udelay have busy loop semantics
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>
Diffstat (limited to 'arch/s390/lib')
-rw-r--r--arch/s390/lib/delay.c30
1 files changed, 14 insertions, 16 deletions
diff --git a/arch/s390/lib/delay.c b/arch/s390/lib/delay.c
index 246a7eb4b680..501dcd4ca4a0 100644
--- a/arch/s390/lib/delay.c
+++ b/arch/s390/lib/delay.c
@@ -12,8 +12,10 @@
#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)
{
@@ -30,26 +32,22 @@ EXPORT_SYMBOL(__delay);
static void __udelay_disabled(unsigned long long usecs)
{
- unsigned long cr0, cr6, new;
- u64 clock_saved, end;
+ unsigned long cr0, cr0_new, psw_mask;
+ struct s390_idle_data idle;
+ u64 end;
end = get_tod_clock() + (usecs << 12);
- clock_saved = local_tick_disable();
__ctl_store(cr0, 0, 0);
- __ctl_store(cr6, 6, 6);
- new = (cr0 & 0xffff00e0) | 0x00000800;
- __ctl_load(new , 0, 0);
- new = 0;
- __ctl_load(new, 6, 6);
- lockdep_off();
- do {
- set_clock_comparator(end);
- enabled_wait();
- } while (get_tod_clock_fast() < end);
- lockdep_on();
+ 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);
- __ctl_load(cr6, 6, 6);
- local_tick_enable(clock_saved);
}
static void __udelay_enabled(unsigned long long usecs)