Subject: [PATCH] linux-acpi: smp_alternatives sleeping in spinlock

[Raz <raziebe@gmail.com>]

From: Raz Ben Yehuda <raziebe@gmail.com>

When booting a kernel with PREEMPT_ENABLE and SLAB_DEBUG, unplugging a processor
results in BUG in slab.
Signed-off-by: Raz Ben Yehuda <raziebe@gmail.com>
---
arch/x86/kernel/alternative.c |   17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)
this bug fix refers to bug numner 11562 in bugzilla.kernel.org

diff -urpN -X dontdiff
linux-2.6.26-5-vanilla/arch/x86/kernel/alternative.c
linux-2.6.26-5-dbg/arch/x86/kernel/alternative.c
--- linux-2.6.26-5-vanilla/arch/x86/kernel/alternative.c	2008-07-13
23:51:29.000000000 +0200
+++ linux-2.6.26-5-dbg/arch/x86/kernel/alternative.c	2008-09-13
15:31:52.000000000 +0200
@@ -13,6 +13,7 @@
 #include <asm/vsyscall.h>
 #include <asm/cacheflush.h>
 #include <asm/io.h>
+#include <linux/semaphore.h>

 #define MAX_PATCH_LEN (255-1)

@@ -279,7 +280,7 @@ struct smp_alt_module {
 	struct list_head next;
 };
 static LIST_HEAD(smp_alt_modules);
-static DEFINE_SPINLOCK(smp_alt);
+static __DECLARE_SEMAPHORE_GENERIC(smp_alt_lock, 1);
 static int smp_mode = 1;	/* protected by smp_alt */

 void alternatives_smp_module_add(struct module *mod, char *name,
@@ -312,12 +313,12 @@ void alternatives_smp_module_add(struct
 		__func__, smp->locks, smp->locks_end,
 		smp->text, smp->text_end, smp->name);

-	spin_lock(&smp_alt);
+	down(&smp_alt_lock);
 	list_add_tail(&smp->next, &smp_alt_modules);
 	if (boot_cpu_has(X86_FEATURE_UP))
 		alternatives_smp_unlock(smp->locks, smp->locks_end,
 					smp->text, smp->text_end);
-	spin_unlock(&smp_alt);
+	up(&smp_alt_lock);
 }

 void alternatives_smp_module_del(struct module *mod)
@@ -327,17 +328,17 @@ void alternatives_smp_module_del(struct
 	if (smp_alt_once || noreplace_smp)
 		return;

-	spin_lock(&smp_alt);
+	down(&smp_alt_lock);
 	list_for_each_entry(item, &smp_alt_modules, next) {
 		if (mod != item->mod)
 			continue;
 		list_del(&item->next);
-		spin_unlock(&smp_alt);
+		up(&smp_alt_lock);
 		DPRINTK("%s: %s\n", __func__, item->name);
 		kfree(item);
 		return;
 	}
-	spin_unlock(&smp_alt);
+	up(&smp_alt_lock);
 }

 void alternatives_smp_switch(int smp)
@@ -359,7 +360,7 @@ void alternatives_smp_switch(int smp)
 		return;
 	BUG_ON(!smp && (num_online_cpus() > 1));

-	spin_lock(&smp_alt);
+	down(&smp_alt_lock);

 	/*
 	 * Avoid unnecessary switches because it forces JIT based VMs to
@@ -383,7 +384,7 @@ void alternatives_smp_switch(int smp)
 						mod->text, mod->text_end);
 	}
 	smp_mode = smp;
-	spin_unlock(&smp_alt);
+	up(&smp_alt_lock);
 }

 #endif