From db7e007fd61ca07e5f3b04cf2168531b074d318d Mon Sep 17 00:00:00 2001 From: Heiko Carstens Date: Sat, 15 Aug 2015 11:42:21 +0200 Subject: [PATCH] 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 Reviewed-by: Martin Schwidefsky Signed-off-by: Martin Schwidefsky --- arch/s390/include/asm/idle.h | 2 ++ arch/s390/include/asm/irq.h | 13 +++++++++++++ arch/s390/include/asm/processor.h | 2 ++ arch/s390/kernel/entry.S | 4 ++++ arch/s390/kernel/entry.h | 1 - arch/s390/lib/delay.c | 30 ++++++++++++++---------------- 6 files changed, 35 insertions(+), 17 deletions(-) diff --git a/arch/s390/include/asm/idle.h b/arch/s390/include/asm/idle.h index 113cd963dbbe..51ff96d9f287 100644 --- a/arch/s390/include/asm/idle.h +++ b/arch/s390/include/asm/idle.h @@ -24,4 +24,6 @@ struct s390_idle_data { extern struct device_attribute dev_attr_idle_count; extern struct device_attribute dev_attr_idle_time_us; +void psw_idle(struct s390_idle_data *, unsigned long); + #endif /* _S390_IDLE_H */ diff --git a/arch/s390/include/asm/irq.h b/arch/s390/include/asm/irq.h index ff95d15a2384..33d26424c2f5 100644 --- a/arch/s390/include/asm/irq.h +++ b/arch/s390/include/asm/irq.h @@ -96,6 +96,19 @@ enum irq_subclass { IRQ_SUBCLASS_SERVICE_SIGNAL = 9, }; +#define CR0_IRQ_SUBCLASS_MASK \ + ((1UL << (63 - 30)) /* Warning Track */ | \ + (1UL << (63 - 48)) /* Malfunction Alert */ | \ + (1UL << (63 - 49)) /* Emergency Signal */ | \ + (1UL << (63 - 50)) /* External Call */ | \ + (1UL << (63 - 52)) /* Clock Comparator */ | \ + (1UL << (63 - 53)) /* CPU Timer */ | \ + (1UL << (63 - 54)) /* Service Signal */ | \ + (1UL << (63 - 57)) /* Interrupt Key */ | \ + (1UL << (63 - 58)) /* Measurement Alert */ | \ + (1UL << (63 - 59)) /* Timing Alert */ | \ + (1UL << (63 - 62))) /* IUCV */ + void irq_subclass_register(enum irq_subclass subclass); void irq_subclass_unregister(enum irq_subclass subclass); 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< #include #include +#include #include #include +#include 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) -- 2.20.1