[PATCH bpf-next v6 01/11] kernel: Implement try_module_get_live
From: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Date: 2022-01-02 16:21:24
Also in:
bpf, lkml, netdev, netfilter-devel
Subsystem:
module support, the rest · Maintainers:
Luis Chamberlain, Petr Pavlu, Daniel Gomez, Sami Tolvanen, Linus Torvalds
Refactor shared functionality between strong_try_module_get and try_module_get into a common helper, and expose try_module_get_live that returns a bool similar to try_module_get. It will be used in the next patch for btf_try_get_module, to eliminate a race between module __init function invocation and module_put from BPF side. Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Jessica Yu <jeyu@kernel.org> Cc: linux-kernel@vger.kernel.org Cc: linux-modules@vger.kernel.org Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> --- include/linux/module.h | 26 +++++++++++++++++++------- kernel/module.c | 20 ++++++++------------ 2 files changed, 27 insertions(+), 19 deletions(-)
diff --git a/include/linux/module.h b/include/linux/module.h
index c9f1200b2312..eb83aaeaa76e 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h@@ -608,17 +608,17 @@ void symbol_put_addr(void *addr); /* Sometimes we know we already have a refcount, and it's easier not to handle the error case (which only happens with rmmod --wait). */ extern void __module_get(struct module *module); - -/* This is the Right Way to get a module: if it fails, it's being removed, - * so pretend it's not there. */ -extern bool try_module_get(struct module *module); - +extern int __try_module_get(struct module *module, bool strong); extern void module_put(struct module *module); #else /*!CONFIG_MODULE_UNLOAD*/ -static inline bool try_module_get(struct module *module) +static inline int __try_module_get(struct module *module, bool strong) { - return !module || module_is_live(module); + if (module && !module_is_live(module)) + return -ENOENT; + if (strong && module && module->state == MODULE_STATE_COMING) + return -EBUSY; + return 0; } static inline void module_put(struct module *module) {
@@ -631,6 +631,18 @@ static inline void __module_get(struct module *module) #endif /* CONFIG_MODULE_UNLOAD */ +/* This is the Right Way to get a module: if it fails, it's being removed, + * so pretend it's not there. */ +static inline bool try_module_get(struct module *module) +{ + return !__try_module_get(module, false); +} +/* Only take reference for modules which have fully initialized */ +static inline bool try_module_get_live(struct module *module) +{ + return !__try_module_get(module, true); +} + /* This is a #define so the string doesn't get put in every .o file */ #define module_name(mod) \ ({ \
diff --git a/kernel/module.c b/kernel/module.c
index 84a9141a5e15..a9bb0a5576c8 100644
--- a/kernel/module.c
+++ b/kernel/module.c@@ -318,12 +318,7 @@ EXPORT_SYMBOL(unregister_module_notifier); static inline int strong_try_module_get(struct module *mod) { BUG_ON(mod && mod->state == MODULE_STATE_UNFORMED); - if (mod && mod->state == MODULE_STATE_COMING) - return -EBUSY; - if (try_module_get(mod)) - return 0; - else - return -ENOENT; + return __try_module_get(mod, true); } static inline void add_taint_module(struct module *mod, unsigned flag,
@@ -1066,24 +1061,25 @@ void __module_get(struct module *module) } EXPORT_SYMBOL(__module_get); -bool try_module_get(struct module *module) +int __try_module_get(struct module *module, bool strong) { - bool ret = true; + int ret = 0; if (module) { preempt_disable(); + if (strong && module->state == MODULE_STATE_COMING) + ret = -EBUSY; /* Note: here, we can fail to get a reference */ - if (likely(module_is_live(module) && + else if (likely(module_is_live(module) && atomic_inc_not_zero(&module->refcnt) != 0)) trace_module_get(module, _RET_IP_); else - ret = false; - + ret = -ENOENT; preempt_enable(); } return ret; } -EXPORT_SYMBOL(try_module_get); +EXPORT_SYMBOL(__try_module_get); void module_put(struct module *module) {
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2.34.1