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Subject[PATCH 3/4] x86/alternatives: get rid of the smp_alt mutex
Date
Previous two patches can make sure the smp_alt_modules will only
be used when UP, so we don't need a mutex to protect the list,
we only need to preempt_disable() when traverse the list.

Signed-off-by: Zhou Chengming <zhouchengming1@huawei.com>
---
arch/x86/kernel/alternative.c | 31 +++++++++++++++----------------
1 file changed, 15 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 5c3f593..7eab6f6 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -485,8 +485,7 @@ struct smp_alt_module {
struct list_head next;
};
static LIST_HEAD(smp_alt_modules);
-static DEFINE_MUTEX(smp_alt);
-static bool uniproc_patched = false; /* protected by smp_alt */
+static bool uniproc_patched = false;

void __init_or_module alternatives_smp_module_add(struct module *mod,
char *name,
@@ -495,18 +494,18 @@ void __init_or_module alternatives_smp_module_add(struct module *mod,
{
struct smp_alt_module *smp;

- mutex_lock(&smp_alt);
+ preempt_disable();
if (!uniproc_patched)
- goto unlock;
+ goto out;

if (num_possible_cpus() == 1)
/* Don't bother remembering, we'll never have to undo it. */
- goto smp_unlock;
+ goto smp_out;

- smp = kzalloc(sizeof(*smp), GFP_KERNEL);
+ smp = kzalloc(sizeof(*smp), GFP_ATOMIC);
if (NULL == smp)
/* we'll run the (safe but slow) SMP code then ... */
- goto unlock;
+ goto out;

smp->mod = mod;
smp->name = name;
@@ -519,19 +518,19 @@ void __init_or_module alternatives_smp_module_add(struct module *mod,
smp->text, smp->text_end, smp->name);

list_add_tail(&smp->next, &smp_alt_modules);
-smp_unlock:
+smp_out:
alternatives_smp_unlock(locks, locks_end, text, text_end);
-unlock:
- mutex_unlock(&smp_alt);
+out:
+ preempt_enable();
}

void __init_or_module alternatives_smp_module_del(struct module *mod)
{
struct smp_alt_module *item;

- mutex_lock(&smp_alt);
+ preempt_disable();
if (!uniproc_patched)
- goto unlock;
+ goto out;

list_for_each_entry(item, &smp_alt_modules, next) {
if (mod != item->mod)
@@ -540,8 +539,8 @@ void __init_or_module alternatives_smp_module_del(struct module *mod)
kfree(item);
break;
}
-unlock:
- mutex_unlock(&smp_alt);
+out:
+ preempt_enable();
}

void alternatives_enable_smp(void)
@@ -551,7 +550,7 @@ void alternatives_enable_smp(void)
/* Why bother if there are no other CPUs? */
BUG_ON(num_possible_cpus() == 1);

- mutex_lock(&smp_alt);
+ preempt_disable();

if (uniproc_patched) {
pr_info("switching to SMP code\n");
@@ -566,7 +565,7 @@ void alternatives_enable_smp(void)
}
uniproc_patched = false;
}
- mutex_unlock(&smp_alt);
+ preempt_enable();
}

/* Return 1 if the address range is reserved for smp-alternatives */
--
1.8.3.1
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