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s390/spinlock: do not yield to a CPU in udelay/mdelay

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It does not make sense to try to relinquish the time slice with diag 0x9c
to a CPU in a state that does not allow to schedule the CPU. The scenario
where this can happen is a CPU waiting in udelay/mdelay while holding a
spin-lock.

Add a CIF bit to tag a CPU in enabled wait and use it to detect that the
yield of a CPU will not be successful and skip the diagnose call.

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky
2015-11-19 11:09:45 +01:00
parent c6f70d3b8a
commit 419123f900
3 changed files with 31 additions and 8 deletions
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12
arch/s390/include/asm/processor.h
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@@ -18,12 +18,14 @@
#define CIF_NOHZ_DELAY 2 /* delay HZ disable for a tick */
#define CIF_FPU 3 /* restore FPU registers */
#define CIF_IGNORE_IRQ 4 /* ignore interrupt (for udelay) */
#define CIF_ENABLED_WAIT 5 /* in enabled wait state */
#define _CIF_MCCK_PENDING _BITUL(CIF_MCCK_PENDING)
#define _CIF_ASCE _BITUL(CIF_ASCE)
#define _CIF_NOHZ_DELAY _BITUL(CIF_NOHZ_DELAY)
#define _CIF_FPU _BITUL(CIF_FPU)
#define _CIF_IGNORE_IRQ _BITUL(CIF_IGNORE_IRQ)
#define _CIF_ENABLED_WAIT _BITUL(CIF_ENABLED_WAIT)
#ifndef __ASSEMBLY__
@@ -52,6 +54,16 @@ static inline int test_cpu_flag(int flag)
return !!(S390_lowcore.cpu_flags & (1UL << flag));
}
/*
* Test CIF flag of another CPU. The caller needs to ensure that
* CPU hotplug can not happen, e.g. by disabling preemption.
*/
static inline int test_cpu_flag_of(int flag, int cpu)
{
struct _lowcore *lc = lowcore_ptr[cpu];
return !!(lc->cpu_flags & (1UL << flag));
}
#define arch_needs_cpu() test_cpu_flag(CIF_NOHZ_DELAY)
/*