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| author | Heiko Carstens <heiko.carstens@de.ibm.com> | 2015-08-15 11:42:21 +0200 |
|---|---|---|
| committer | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2015-10-14 14:32:13 +0200 |
| commit | db7e007fd61ca07e5f3b04cf2168531b074d318d (patch) | |
| tree | 998423a5b6cfdc90b2ce91c271fa3ba0ffc380f7 /arch/s390/include/asm/processor.h | |
| parent | 0c5a69f432ba1e586ac6ae5e4311c2f1cbd051fa (diff) | |
| download | linux-db7e007fd61ca07e5f3b04cf2168531b074d318d.tar.bz2 | |
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/include/asm/processor.h')
| -rw-r--r-- | arch/s390/include/asm/processor.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h index 5900877bb19c..9e1cdcf8d124 100644 --- a/arch/s390/include/asm/processor.h +++ b/arch/s390/include/asm/processor.h @@ -15,11 +15,13 @@ #define CIF_ASCE 1 /* user asce needs fixup / uaccess */ #define CIF_NOHZ_DELAY 2 /* delay HZ disable for a tick */ #define CIF_FPU 3 /* restore vector registers */ +#define CIF_IGNORE_IRQ 4 /* ignore interrupt (for udelay) */ #define _CIF_MCCK_PENDING (1<<CIF_MCCK_PENDING) #define _CIF_ASCE (1<<CIF_ASCE) #define _CIF_NOHZ_DELAY (1<<CIF_NOHZ_DELAY) #define _CIF_FPU (1<<CIF_FPU) +#define _CIF_IGNORE_IRQ (1<<CIF_IGNORE_IRQ) #ifndef __ASSEMBLY__ |