3.16.42-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Michal Hocko <mhocko@xxxxxxxx> commit 777c6e0daebb3fcefbbd6f620410a946b07ef6d0 upstream. Yu Zhao has noticed that __unregister_cpu_notifier only unregisters its notifiers when HOTPLUG_CPU=y while the registration might succeed even when HOTPLUG_CPU=n if MODULE is enabled. This means that e.g. zswap might keep a stale notifier on the list on the manual clean up during the pool tear down and thus corrupt the list. Resulting in the following [ 144.964346] BUG: unable to handle kernel paging request at ffff880658a2be78 [ 144.971337] IP: [<ffffffffa290b00b>] raw_notifier_chain_register+0x1b/0x40 <snipped> [ 145.122628] Call Trace: [ 145.125086] [<ffffffffa28e5cf8>] __register_cpu_notifier+0x18/0x20 [ 145.131350] [<ffffffffa2a5dd73>] zswap_pool_create+0x273/0x400 [ 145.137268] [<ffffffffa2a5e0fc>] __zswap_param_set+0x1fc/0x300 [ 145.143188] [<ffffffffa2944c1d>] ? trace_hardirqs_on+0xd/0x10 [ 145.149018] [<ffffffffa2908798>] ? kernel_param_lock+0x28/0x30 [ 145.154940] [<ffffffffa2a3e8cf>] ? __might_fault+0x4f/0xa0 [ 145.160511] [<ffffffffa2a5e237>] zswap_compressor_param_set+0x17/0x20 [ 145.167035] [<ffffffffa2908d3c>] param_attr_store+0x5c/0xb0 [ 145.172694] [<ffffffffa290848d>] module_attr_store+0x1d/0x30 [ 145.178443] [<ffffffffa2b2b41f>] sysfs_kf_write+0x4f/0x70 [ 145.183925] [<ffffffffa2b2a5b9>] kernfs_fop_write+0x149/0x180 [ 145.189761] [<ffffffffa2a99248>] __vfs_write+0x18/0x40 [ 145.194982] [<ffffffffa2a9a412>] vfs_write+0xb2/0x1a0 [ 145.200122] [<ffffffffa2a9a732>] SyS_write+0x52/0xa0 [ 145.205177] [<ffffffffa2ff4d97>] entry_SYSCALL_64_fastpath+0x12/0x17 This can be even triggered manually by changing /sys/module/zswap/parameters/compressor multiple times. Fix this issue by making unregister APIs symmetric to the register so there are no surprises. Fixes: 47e627bc8c9a ("[PATCH] hotplug: Allow modules to use the cpu hotplug notifiers even if !CONFIG_HOTPLUG_CPU") Reported-and-tested-by: Yu Zhao <yuzhao@xxxxxxxxxx> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> Cc: linux-mm@xxxxxxxxx Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Dan Streetman <ddstreet@xxxxxxxx> Link: http://lkml.kernel.org/r/20161207135438.4310-1-mhocko@xxxxxxxxxx Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> [bwh: Backported to 3.16: keep definition of cpu_notify_nofail() conditional on CONFIG_HOTPLUG_CPU] Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> --- --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -122,22 +122,16 @@ enum { { .notifier_call = fn, .priority = pri }; \ __register_cpu_notifier(&fn##_nb); \ } -#else /* #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE) */ -#define cpu_notifier(fn, pri) do { (void)(fn); } while (0) -#define __cpu_notifier(fn, pri) do { (void)(fn); } while (0) -#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE) */ -#ifdef CONFIG_HOTPLUG_CPU extern int register_cpu_notifier(struct notifier_block *nb); extern int __register_cpu_notifier(struct notifier_block *nb); extern void unregister_cpu_notifier(struct notifier_block *nb); extern void __unregister_cpu_notifier(struct notifier_block *nb); -#else -#ifndef MODULE -extern int register_cpu_notifier(struct notifier_block *nb); -extern int __register_cpu_notifier(struct notifier_block *nb); -#else +#else /* #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE) */ +#define cpu_notifier(fn, pri) do { (void)(fn); } while (0) +#define __cpu_notifier(fn, pri) do { (void)(fn); } while (0) + static inline int register_cpu_notifier(struct notifier_block *nb) { return 0; @@ -147,7 +141,6 @@ static inline int __register_cpu_notifie { return 0; } -#endif static inline void unregister_cpu_notifier(struct notifier_block *nb) { --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -210,12 +210,6 @@ static int cpu_notify(unsigned long val, return __cpu_notify(val, v, -1, NULL); } -#ifdef CONFIG_HOTPLUG_CPU - -static void cpu_notify_nofail(unsigned long val, void *v) -{ - BUG_ON(cpu_notify(val, v)); -} EXPORT_SYMBOL(register_cpu_notifier); EXPORT_SYMBOL(__register_cpu_notifier); @@ -233,6 +227,13 @@ void __ref __unregister_cpu_notifier(str } EXPORT_SYMBOL(__unregister_cpu_notifier); +#ifdef CONFIG_HOTPLUG_CPU + +static void cpu_notify_nofail(unsigned long val, void *v) +{ + BUG_ON(cpu_notify(val, v)); +} + /** * clear_tasks_mm_cpumask - Safely clear tasks' mm_cpumask for a CPU * @cpu: a CPU id