From db7e007fd61ca07e5f3b04cf2168531b074d318d Mon Sep 17 00:00:00 2001 From: Heiko Carstens Date: Sat, 15 Aug 2015 11:42:21 +0200 Subject: 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/kernel/entry.S | 4 ++++ arch/s390/kernel/entry.h | 1 - 2 files changed, 4 insertions(+), 1 deletion(-) (limited to 'arch/s390/kernel') diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S index d653a87d66b5..857b6526d298 100644 --- a/arch/s390/kernel/entry.S +++ b/arch/s390/kernel/entry.S @@ -563,6 +563,8 @@ ENTRY(io_int_handler) stmg %r8,%r9,__PT_PSW(%r11) mvc __PT_INT_CODE(12,%r11),__LC_SUBCHANNEL_ID xc __PT_FLAGS(8,%r11),__PT_FLAGS(%r11) + TSTMSK __LC_CPU_FLAGS,_CIF_IGNORE_IRQ + jo .Lio_restore TRACE_IRQS_OFF xc __SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15) .Lio_loop: @@ -738,6 +740,8 @@ ENTRY(ext_int_handler) mvc __PT_INT_PARM(4,%r11),__LC_EXT_PARAMS mvc __PT_INT_PARM_LONG(8,%r11),0(%r1) xc __PT_FLAGS(8,%r11),__PT_FLAGS(%r11) + TSTMSK __LC_CPU_FLAGS,_CIF_IGNORE_IRQ + jo .Lio_restore TRACE_IRQS_OFF xc __SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15) lgr %r2,%r11 # pass pointer to pt_regs diff --git a/arch/s390/kernel/entry.h b/arch/s390/kernel/entry.h index 3eecd0f7adb2..b7019ab74070 100644 --- a/arch/s390/kernel/entry.h +++ b/arch/s390/kernel/entry.h @@ -16,7 +16,6 @@ void io_int_handler(void); void mcck_int_handler(void); void restart_int_handler(void); void restart_call_handler(void); -void psw_idle(struct s390_idle_data *, unsigned long); asmlinkage long do_syscall_trace_enter(struct pt_regs *regs); asmlinkage void do_syscall_trace_exit(struct pt_regs *regs); -- cgit v1.2.3