From: Michal Hocko Date: Wed, 7 Dec 2016 13:54:38 +0000 (+0100) Subject: hotplug: Make register and unregister notifier API symmetric X-Git-Tag: v3.2.87~168 X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=commitdiff_plain;h=2bdea84253130dc22c3e3d7a7e9013d02d21d108 hotplug: Make register and unregister notifier API symmetric 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: [] raw_notifier_chain_register+0x1b/0x40 [ 145.122628] Call Trace: [ 145.125086] [] __register_cpu_notifier+0x18/0x20 [ 145.131350] [] zswap_pool_create+0x273/0x400 [ 145.137268] [] __zswap_param_set+0x1fc/0x300 [ 145.143188] [] ? trace_hardirqs_on+0xd/0x10 [ 145.149018] [] ? kernel_param_lock+0x28/0x30 [ 145.154940] [] ? __might_fault+0x4f/0xa0 [ 145.160511] [] zswap_compressor_param_set+0x17/0x20 [ 145.167035] [] param_attr_store+0x5c/0xb0 [ 145.172694] [] module_attr_store+0x1d/0x30 [ 145.178443] [] sysfs_kf_write+0x4f/0x70 [ 145.183925] [] kernfs_fop_write+0x149/0x180 [ 145.189761] [] __vfs_write+0x18/0x40 [ 145.194982] [] vfs_write+0xb2/0x1a0 [ 145.200122] [] SyS_write+0x52/0xa0 [ 145.205177] [] 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 Signed-off-by: Michal Hocko Cc: linux-mm@kvack.org Cc: Andrew Morton Cc: Dan Streetman Link: http://lkml.kernel.org/r/20161207135438.4310-1-mhocko@kernel.org Signed-off-by: Thomas Gleixner [bwh: Backported to 3.2: - The lockless (__-prefixed) variants don't exist - Keep definition of cpu_notify_nofail() conditional on CONFIG_HOTPLUG_CPU] Signed-off-by: Ben Hutchings --- diff --git a/include/linux/cpu.h b/include/linux/cpu.h index 9c3e071900c0..21b1e9789a80 100644 --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -112,22 +112,16 @@ 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) -#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE) */ -#ifdef CONFIG_HOTPLUG_CPU extern int register_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); -#else +#else /* #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE) */ +#define cpu_notifier(fn, pri) do { (void)(fn); } while (0) + static inline int register_cpu_notifier(struct notifier_block *nb) { return 0; } -#endif static inline void unregister_cpu_notifier(struct notifier_block *nb) { diff --git a/kernel/cpu.c b/kernel/cpu.c index 82c91f1b715a..f735a58bf7b4 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -176,12 +176,6 @@ static int cpu_notify(unsigned long val, void *v) 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); void __ref unregister_cpu_notifier(struct notifier_block *nb) @@ -192,6 +186,13 @@ void __ref unregister_cpu_notifier(struct notifier_block *nb) } 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)); +} + static inline void check_for_tasks(int cpu) { struct task_struct *p;