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Subject[PATCH 1/4] x86/alternatives: free smp_alt_modules when enable smp
In the current code, we don't free smp_alt_modules when enable smp,
so have to wait module unload to call alternatives_smp_module_del()
to free its smp_alt_module. This strategy has shortcomings.

First, maybe some modules don't unload after smp enabled, so these
smp_alt_modules won't be freed even they are useless anymore. Second,
every module has to call alternatives_smp_module_del() when unload
to see if it's in the list even after smp enabled, it's complete
useless work.

And more important, alternatives_smp_module_del() will not traverse
the list after smp enabled, so we don't need a mutex to protect
the list, only need to use preempt_disable().

We can make sure smp_alt_modules will be useless after enable smp,
so free it all. And alternatives_smp_module_del() can return directly
when !uniproc_patched to avoid a list traversal.

Signed-off-by: Zhou Chengming <>
arch/x86/kernel/alternative.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 3344d33..8549269 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -534,6 +534,9 @@ void __init_or_module alternatives_smp_module_del(struct module *mod)
struct smp_alt_module *item;

+ if (!uniproc_patched)
+ goto unlock;
list_for_each_entry(item, &smp_alt_modules, next) {
if (mod != item->mod)
@@ -541,12 +544,13 @@ void __init_or_module alternatives_smp_module_del(struct module *mod)

void alternatives_enable_smp(void)
- struct smp_alt_module *mod;
+ struct smp_alt_module *mod, *tmp;

/* Why bother if there are no other CPUs? */
BUG_ON(num_possible_cpus() == 1);
@@ -558,9 +562,12 @@ void alternatives_enable_smp(void)
BUG_ON(num_online_cpus() != 1);
clear_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
clear_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
- list_for_each_entry(mod, &smp_alt_modules, next)
+ list_for_each_entry_safe(mod, tmp, &smp_alt_modules, next) {
alternatives_smp_lock(mod->locks, mod->locks_end,
mod->text, mod->text_end);
+ list_del(&mod->next);
+ kfree(mod);
+ }
uniproc_patched = false;
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