x86/mce/mcelog: Use xchg() to get and clear the flags

JIRA: https://issues.redhat.com/browse/RHEL-118444

commit 325c337
Author: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Date:   Fri Oct 25 10:45:53 2024 +0800

    x86/mce/mcelog: Use xchg() to get and clear the flags

    Using xchg() to atomically get and clear the MCE log buffer flags,
    streamlines the code and reduces the text size by 20 bytes.

      $ size dev-mcelog.o.*

           text        data     bss     dec     hex filename
           3013         360     160    3533     dcd dev-mcelog.o.old
           2993         360     160    3513     db9 dev-mcelog.o.new

    No functional changes intended.

    Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
    Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
    Reviewed-by: Tony Luck <tony.luck@intel.com>
    Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
    Reviewed-by: Sohil Mehta <sohil.mehta@intel.com>
    Link: https://lore.kernel.org/r/20241025024602.24318-2-qiuxu.zhuo@intel.com

Signed-off-by: David Arcari <darcari@redhat.com>

Author: darcari

arch/x86/kernel/cpu/mce/dev-mcelog.c

@@ -264,15 +264,8 @@ static long mce_chrdev_ioctl(struct file *f, unsigned int cmd,
 		return put_user(sizeof(struct mce), p);
 	case MCE_GET_LOG_LEN:
 		return put_user(mcelog->len, p);
-	case MCE_GETCLEAR_FLAGS: {
-		unsigned flags;
-
-		do {
-			flags = mcelog->flags;
-		} while (cmpxchg(&mcelog->flags, flags, 0) != flags);
-
-		return put_user(flags, p);
-	}
+	case MCE_GETCLEAR_FLAGS:
+		return put_user(xchg(&mcelog->flags, 0), p);
 	default:
 		return -ENOTTY;
 	}