mirror of https://gitee.com/openkylin/linux.git
module: Remove stop_machine from module unloading
Remove stop_machine from module unloading by adding new reference counting algorithm. This atomic refcounter works like a semaphore, it can get (be incremented) only when the counter is not 0. When loading a module, kmodule subsystem sets the counter MODULE_REF_BASE (= 1). And when unloading the module, it subtracts MODULE_REF_BASE from the counter. If no one refers the module, the refcounter becomes 0 and we can remove the module safely. If someone referes it, we try to recover the counter by adding MODULE_REF_BASE unless the counter becomes 0, because the referrer can put the module right before recovering. If the recovering is failed, we can get the 0 refcount and it never be incremented again, it can be removed safely too. Note that __module_get() forcibly gets the module refcounter, users should use try_module_get() instead of that. Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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@ -42,7 +42,6 @@
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#include <linux/vermagic.h>
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#include <linux/notifier.h>
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#include <linux/sched.h>
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#include <linux/stop_machine.h>
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#include <linux/device.h>
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#include <linux/string.h>
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#include <linux/mutex.h>
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@ -98,7 +97,7 @@
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* 1) List of modules (also safely readable with preempt_disable),
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* 2) module_use links,
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* 3) module_addr_min/module_addr_max.
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* (delete uses stop_machine/add uses RCU list operations). */
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* (delete and add uses RCU list operations). */
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DEFINE_MUTEX(module_mutex);
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EXPORT_SYMBOL_GPL(module_mutex);
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static LIST_HEAD(modules);
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@ -628,14 +627,23 @@ static char last_unloaded_module[MODULE_NAME_LEN+1];
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EXPORT_TRACEPOINT_SYMBOL(module_get);
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/* MODULE_REF_BASE is the base reference count by kmodule loader. */
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#define MODULE_REF_BASE 1
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/* Init the unload section of the module. */
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static int module_unload_init(struct module *mod)
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{
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/*
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* Initialize reference counter to MODULE_REF_BASE.
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* refcnt == 0 means module is going.
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*/
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atomic_set(&mod->refcnt, MODULE_REF_BASE);
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INIT_LIST_HEAD(&mod->source_list);
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INIT_LIST_HEAD(&mod->target_list);
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/* Hold reference count during initialization. */
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atomic_set(&mod->refcnt, 1);
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atomic_inc(&mod->refcnt);
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return 0;
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}
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@ -734,39 +742,39 @@ static inline int try_force_unload(unsigned int flags)
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}
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#endif /* CONFIG_MODULE_FORCE_UNLOAD */
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struct stopref
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/* Try to release refcount of module, 0 means success. */
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static int try_release_module_ref(struct module *mod)
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{
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struct module *mod;
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int flags;
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int *forced;
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};
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int ret;
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/* Whole machine is stopped with interrupts off when this runs. */
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static int __try_stop_module(void *_sref)
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{
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struct stopref *sref = _sref;
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/* Try to decrement refcnt which we set at loading */
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ret = atomic_sub_return(MODULE_REF_BASE, &mod->refcnt);
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BUG_ON(ret < 0);
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if (ret)
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/* Someone can put this right now, recover with checking */
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ret = atomic_add_unless(&mod->refcnt, MODULE_REF_BASE, 0);
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/* If it's not unused, quit unless we're forcing. */
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if (module_refcount(sref->mod) != 0) {
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if (!(*sref->forced = try_force_unload(sref->flags)))
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return -EWOULDBLOCK;
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}
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/* Mark it as dying. */
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sref->mod->state = MODULE_STATE_GOING;
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return 0;
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return ret;
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}
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static int try_stop_module(struct module *mod, int flags, int *forced)
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{
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struct stopref sref = { mod, flags, forced };
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/* If it's not unused, quit unless we're forcing. */
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if (try_release_module_ref(mod) != 0) {
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*forced = try_force_unload(flags);
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if (!(*forced))
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return -EWOULDBLOCK;
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}
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return stop_machine(__try_stop_module, &sref, NULL);
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/* Mark it as dying. */
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mod->state = MODULE_STATE_GOING;
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return 0;
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}
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unsigned long module_refcount(struct module *mod)
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{
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return (unsigned long)atomic_read(&mod->refcnt);
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return (unsigned long)atomic_read(&mod->refcnt) - MODULE_REF_BASE;
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}
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EXPORT_SYMBOL(module_refcount);
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@ -921,11 +929,11 @@ bool try_module_get(struct module *module)
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if (module) {
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preempt_disable();
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if (likely(module_is_live(module))) {
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atomic_inc(&module->refcnt);
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/* Note: here, we can fail to get a reference */
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if (likely(module_is_live(module) &&
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atomic_inc_not_zero(&module->refcnt) != 0))
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trace_module_get(module, _RET_IP_);
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} else
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else
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ret = false;
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preempt_enable();
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@ -936,9 +944,12 @@ EXPORT_SYMBOL(try_module_get);
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void module_put(struct module *module)
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{
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int ret;
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if (module) {
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preempt_disable();
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atomic_dec(&module->refcnt);
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ret = atomic_dec_if_positive(&module->refcnt);
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WARN_ON(ret < 0); /* Failed to put refcount */
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trace_module_put(module, _RET_IP_);
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preempt_enable();
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}
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