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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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appldata	[S390] appldata: fix dev_get_stats 64 bit conversion	15 years ago
boot	[S390] Add support for LZO-compressed kernels.	15 years ago
crypto	[S390] cleanup facility list handling	14 years ago
hypfs	Merge branch 'for-linus' of git://git390.marist.edu/pub/scm/linux-2.6	14 years ago
include/asm	[S390] mm: add devmem_is_allowed() for STRICT_DEVMEM checking	14 years ago
kernel	[S390] nohz/s390: fix arch_needs_cpu() return value on offline cpus	14 years ago
kvm	[S390] cleanup facility list handling	14 years ago
lib	[S390] nmi: fix clock comparator revalidation	14 years ago
math-emu	tree-wide: fix assorted typos all over the place	15 years ago
mm	[S390] fix get_user_pages_fast	14 years ago
oprofile	…
Kbuild	[S390] standardize Kbuild rules	14 years ago
Kconfig	[S390] ftrace: select HAVE_C_RECORDMCOUNT	14 years ago
Kconfig.debug	[S390] mm: add devmem_is_allowed() for STRICT_DEVMEM checking	14 years ago
Makefile	[S390] Add config option for z196 code generation.	14 years ago
defconfig	defconfig reduction	15 years ago