kexec: use a mutex for locking rather than xchg()

Functionally the same, but more conventional.

Cc: Huang Ying <ying.huang@intel.com>
Tested-by: Vivek Goyal <vgoyal@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/kexec.c

@@ -12,7 +12,7 @@
 #include <linux/slab.h>
 #include <linux/fs.h>
 #include <linux/kexec.h>
-#include <linux/spinlock.h>
+#include <linux/mutex.h>
 #include <linux/list.h>
 #include <linux/highmem.h>
 #include <linux/syscalls.h>
@@ -924,19 +924,14 @@ static int kimage_load_segment(struct kimage *image,
  */
 struct kimage *kexec_image;
 struct kimage *kexec_crash_image;
-/*
- * A home grown binary mutex.
- * Nothing can wait so this mutex is safe to use
- * in interrupt context :)
- */
-static int kexec_lock;
+
+static DEFINE_MUTEX(kexec_mutex);
 
 asmlinkage long sys_kexec_load(unsigned long entry, unsigned long nr_segments,
 				struct kexec_segment __user *segments,
 				unsigned long flags)
 {
 	struct kimage **dest_image, *image;
-	int locked;
 	int result;
 
 	/* We only trust the superuser with rebooting the system. */
@@ -972,8 +967,7 @@ asmlinkage long sys_kexec_load(unsigned long entry, unsigned long nr_segments,
 	 *
 	 * KISS: always take the mutex.
 	 */
-	locked = xchg(&kexec_lock, 1);
-	if (locked)
+	if (!mutex_trylock(&kexec_mutex))
 		return -EBUSY;
 
 	dest_image = &kexec_image;
@@ -1015,8 +1009,7 @@ asmlinkage long sys_kexec_load(unsigned long entry, unsigned long nr_segments,
 	image = xchg(dest_image, image);
 
 out:
-	locked = xchg(&kexec_lock, 0); /* Release the mutex */
-	BUG_ON(!locked);
+	mutex_unlock(&kexec_mutex);
 	kimage_free(image);
 
 	return result;
@@ -1063,10 +1056,7 @@ asmlinkage long compat_sys_kexec_load(unsigned long entry,
 
 void crash_kexec(struct pt_regs *regs)
 {
-	int locked;
-
-
-	/* Take the kexec_lock here to prevent sys_kexec_load
+	/* Take the kexec_mutex here to prevent sys_kexec_load
 	 * running on one cpu from replacing the crash kernel
 	 * we are using after a panic on a different cpu.
 	 *
@@ -1074,8 +1064,7 @@ void crash_kexec(struct pt_regs *regs)
 	 * of memory the xchg(&kexec_crash_image) would be
 	 * sufficient.  But since I reuse the memory...
 	 */
-	locked = xchg(&kexec_lock, 1);
-	if (!locked) {
+	if (mutex_trylock(&kexec_mutex)) {
 		if (kexec_crash_image) {
 			struct pt_regs fixed_regs;
 			crash_setup_regs(&fixed_regs, regs);
@@ -1083,8 +1072,7 @@ void crash_kexec(struct pt_regs *regs)
 			machine_crash_shutdown(&fixed_regs);
 			machine_kexec(kexec_crash_image);
 		}
-		locked = xchg(&kexec_lock, 0);
-		BUG_ON(!locked);
+		mutex_unlock(&kexec_mutex);
 	}
 }
 
@@ -1434,7 +1422,7 @@ int kernel_kexec(void)
 {
 	int error = 0;
 
-	if (xchg(&kexec_lock, 1))
+	if (!mutex_trylock(&kexec_mutex))
 		return -EBUSY;
 	if (!kexec_image) {
 		error = -EINVAL;
@@ -1498,8 +1486,6 @@ int kernel_kexec(void)
 #endif
 
  Unlock:
-	if (!xchg(&kexec_lock, 0))
-		BUG();
-
+	mutex_unlock(&kexec_mutex);
 	return error;
 }