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Heiko Carstens 398812159e [S390] nohz/s390: fix arch_needs_cpu() return value on offline cpus ... This fixes the same problem as described in the patch "nohz: fix printk_needs_cpu() return value on offline cpus" for the arch_needs_cpu() primitive: arch_needs_cpu() may return 1 if called on offline cpus. When a cpu gets offlined it schedules the idle process which, before killing its own cpu, will call tick_nohz_stop_sched_tick(). That function in turn will call arch_needs_cpu() in order to check if the local tick can be disabled. On offline cpus this function should naturally return 0 since regardless if the tick gets disabled or not the cpu will be dead short after. That is besides the fact that __cpu_disable() should already have made sure that no interrupts on the offlined cpu will be delivered anyway. In this case it prevents tick_nohz_stop_sched_tick() to call select_nohz_load_balancer(). No idea if that really is a problem. However what made me debug this is that on 2.6.32 the function get_nohz_load_balancer() is used within __mod_timer() to select a cpu on which a timer gets enqueued. If arch_needs_cpu() returns 1 then the nohz_load_balancer cpu doesn't get updated when a cpu gets offlined. It may contain the cpu number of an offline cpu. In turn timers get enqueued on an offline cpu and not very surprisingly they never expire and cause system hangs. This has been observed 2.6.32 kernels. On current kernels __mod_timer() uses get_nohz_timer_target() which doesn't have that problem. However there might be other problems because of the too early exit tick_nohz_stop_sched_tick() in case a cpu goes offline. This specific bug was indrocuded with 3c5d92a0 "nohz: Introduce arch_needs_cpu". In this case a cpu hotplug notifier is used to fix the issue in order to keep the normal/fast path small. All we need to do is to clear the condition that makes arch_needs_cpu() return 1 since it is just a performance improvement which is supposed to keep the local tick running for a short period if a cpu goes idle. Nothing special needs to be done except for clearing the condition. Cc: stable@kernel.org Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>		14 years ago
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vdso32	[S390] vdso: get rid of redefinition warnings	14 years ago
vdso64	[S390] vdso: get rid of redefinition warnings	14 years ago
Makefile	[S390] add support for compressed kernels	15 years ago
asm-offsets.c	[S390] vdso: get rid of redefinition warnings	14 years ago
audit.c	…
audit.h	…
base.S	[S390] Cleanup struct _lowcore usage and defines.	15 years ago
bitmap.c	[S390] move EXPORT_SYMBOLs to definitions	16 years ago
compat_audit.c	…
compat_exec_domain.c	…
compat_linux.c	BKL: remove extraneous #include <smp_lock.h>	14 years ago
compat_linux.h	Mark arguments to certain syscalls as being const	15 years ago
compat_ptrace.h	[S390] remove ieee_instruction_pointer from thread_struct	14 years ago
compat_signal.c	[S390] 64-bit register support for 31-bit processes	16 years ago
compat_wrapper.S	[S390] wire up prlimit64 and fanotify* syscalls	15 years ago
cpcmd.c	[S390] convert cpcmd printks to pr_xxx macros.	16 years ago
crash.c	…
debug.c	llseek: automatically add .llseek fop	15 years ago
diag.c	…
dis.c	[S390] add z196 instructions to kernel disassembler	14 years ago
early.c	[S390] facility detection: remove unused variable	14 years ago
ebcdic.c	…
entry.S	[S390] fix kprobes single stepping	14 years ago
entry.h	[S390] cleanup lowcore access from external interrupts	14 years ago
entry64.S	[S390] fix kprobes single stepping	14 years ago
ftrace.c	Merge branch 'tracing-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip	15 years ago
head.S	[S390] Add config option for z196 code generation.	14 years ago
head31.S	[S390] correct address of _stext with CONFIG_SHARED_KERNEL=y	15 years ago
head64.S	[S390] correct address of _stext with CONFIG_SHARED_KERNEL=y	15 years ago
init_task.c	Use new __init_task_data macro in arch init_task.c files.	16 years ago
ipl.c	sysfs: add struct file* to bin_attr callbacks	15 years ago
irq.c	[S390] Fix init irq proc build break.	16 years ago
kprobes.c	[S390] kprobes: Fix the return address of multiple kretprobes	14 years ago
machine_kexec.c	[S390] smp: always reboot on cpu 0	15 years ago
mcount.S	[S390] improve mcount code	16 years ago
mcount64.S	[S390] improve mcount code	16 years ago
mem_detect.c	Fix IRQ flag handling naming	15 years ago
module.c	modules: Fix module_bug_list list corruption race	15 years ago
nmi.c	[S390] nmi: fix clock comparator revalidation	14 years ago
process.c	[S390] cpu hotplug/idle: move cpu_die call to enabled context	14 years ago
processor.c	[S390] smp: use correct cpu address in print_cpu_info()	14 years ago
ptrace.c	ptrace: change signature of arch_ptrace()	14 years ago
reipl.S	[S390] Cleanup struct _lowcore usage and defines.	15 years ago
reipl64.S	[S390] Cleanup struct _lowcore usage and defines.	15 years ago
relocate_kernel.S	…
relocate_kernel64.S	…
s390_ext.c	[S390] cleanup lowcore access from external interrupts	14 years ago
s390_ksyms.c	[S390] move EXPORT_SYMBOLs to definitions	16 years ago
sclp.S	Merge branch 'for-next' into for-linus	15 years ago
setup.c	[S390] Add z196 machine type to setup_hwcaps	14 years ago
signal.c	[S390] add breaking event address for user space	15 years ago
smp.c	[S390] cleanup facility list handling	14 years ago
stacktrace.c	…
suspend.c	[S390] hibernate: make sure pfn_is_nosave handles lowcore pages	16 years ago
switch_cpu.S	[S390] Cleanup struct _lowcore usage and defines.	15 years ago
switch_cpu64.S	[S390] Cleanup struct _lowcore usage and defines.	15 years ago
swsusp_asm64.S	Merge branch 'for-35' of git://repo.or.cz/linux-kbuild	15 years ago
sys_s390.c	[S390] sys_personality: follow u_long to unsigned int conversion	15 years ago
syscalls.S	[S390] wire up prlimit64 and fanotify* syscalls	15 years ago
sysinfo.c	[S390] topology: add SCHED_MC config option	14 years ago
time.c	[S390] cleanup lowcore access from external interrupts	14 years ago
topology.c	[S390] topology: fix cpu masks for topology=off case	14 years ago
traps.c	[S390] remove ieee_instruction_pointer from thread_struct	14 years ago
vdso.c	[S390] cleanup facility list handling	14 years ago
vmlinux.lds.S	[S390] Enable kmemleak on s390.	16 years ago
vtime.c	[S390] nohz/s390: fix arch_needs_cpu() return value on offline cpus	14 years ago