linux-kernel - [PATCH 3/4] x86/alternatives: get rid of the smp

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Date:   Sat, 28 Oct 2017 20:50:56 +0800
From:   Zhou Chengming <zhouchengming1@...wei.com>
To:     <mhiramat@...nel.org>, <bp@...e.de>, <peterz@...radead.org>,
        <ananth@...ux.vnet.ibm.com>, <anil.s.keshavamurthy@...el.com>,
        <davem@...emloft.net>, <tglx@...utronix.de>, <jkosina@...e.cz>,
        <rostedt@...dmis.org>, <mjurczyk@...gle.com>
CC:     <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
        <zhouchengming1@...wei.com>
Subject: [PATCH 3/4] x86/alternatives: get rid of the smp_alt mutex

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@...wei.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