Messages in this thread | | | From | Dexuan Cui <> | Subject | static_branch_enable() does not work from a __init function? | Date | Wed, 16 Dec 2020 03:54:29 +0000 |
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Hi, The below init_module() prints "foo: false". This is strange since static_branch_enable() is called before the static_branch_unlikely(). This strange behavior happens to v5.10 and an old v5.4 kernel.
If I remove the "__init" marker from the init_module() function, then I get the expected output of "foo: true"! I guess here I'm missing something with Static Keys?
#include <linux/module.h> #include <linux/kernel.h> #include <linux/jump_label.h>
static DEFINE_STATIC_KEY_FALSE(enable_foo);
int __init init_module(void) { static_branch_enable(&enable_foo);
if (static_branch_unlikely(&enable_foo)) printk("foo: true\n"); else printk("foo: false\n");
return 0; }
void cleanup_module(void) { static_branch_disable(&enable_foo); }
MODULE_LICENSE("GPL");
PS, I originally found: in arch/x86/kvm/vmx/vmx.c: vmx_init(), it looks like the line "static_branch_enable(&enable_evmcs);" does not take effect in a v5.4-based kernel, but does take effect in the v5.10 kernel in the same x86-64 virtual machine on Hyper-V, so I made the above test module to test static_branch_enable(), and found that static_branch_enable() in the test module does not work with both v5.10 and my v5.4 kernel, if the __init marker is used.
Thanks, -- Dexuan
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