linux-kernel - [PATCH 3.16 270/294] x86/boot: Add CONFIG_PARAVIRT_SPINLOCKS quirk to arch/x86/boot/compressed/misc.h

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Message-ID: <lsq.1510009382.716473741@decadent.org.uk>
Date:   Mon, 06 Nov 2017 23:03:02 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Ingo Molnar" <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Arnd Bergmann" <arnd@...db.de>
Subject: [PATCH 3.16 270/294] x86/boot: Add CONFIG_PARAVIRT_SPINLOCKS
 quirk to arch/x86/boot/compressed/misc.h

3.16.50-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ingo Molnar <mingo@...nel.org>

commit 927392d73a97d8d235bb65400e2e3c7f0bec2b6f upstream.

Linus reported the following new warning on x86 allmodconfig with GCC 5.1:

  > ./arch/x86/include/asm/spinlock.h: In function ‘arch_spin_lock’:
  > ./arch/x86/include/asm/spinlock.h:119:3: warning: implicit declaration
  > of function ‘__ticket_lock_spinning’ [-Wimplicit-function-declaration]
  >    __ticket_lock_spinning(lock, inc.tail);
  >    ^

This warning triggers because of these hacks in misc.h:

  /*
   * we have to be careful, because no indirections are allowed here, and
   * paravirt_ops is a kind of one. As it will only run in baremetal anyway,
   * we just keep it from happening
   */
  #undef CONFIG_PARAVIRT
  #undef CONFIG_KASAN

But these hacks were not updated when CONFIG_PARAVIRT_SPINLOCKS was added,
and eventually (with the introduction of queued paravirt spinlocks in
recent kernels) this created an invalid Kconfig combination and broke
the build.

So add a CONFIG_PARAVIRT_SPINLOCKS #undef line as well.

Also remove the _ASM_X86_DESC_H quirk: that undocumented quirk
was originally added ages ago, in:

  099e1377269a ("x86: use ELF format in compressed images.")

and I went back to that kernel (and fixed up the main Makefile
which didn't build anymore) and checked what failure it
avoided: it avoided an include file dependencies related
build failure related to our old x86-platforms code.

That old code is long gone, the header dependencies got cleaned
up, and the build does not fail anymore with the totality of
asm/desc.h included - so remove the quirk.

Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/boot/compressed/misc.h | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -2,14 +2,13 @@
 #define BOOT_COMPRESSED_MISC_H

 /*
- * we have to be careful, because no indirections are allowed here, and
- * paravirt_ops is a kind of one. As it will only run in baremetal anyway,
- * we just keep it from happening
+ * Special hack: we have to be careful, because no indirections are allowed here,
+ * and paravirt_ops is a kind of one. As it will only run in baremetal anyway,
+ * we just keep it from happening. (This list needs to be extended when new
+ * paravirt and debugging variants are added.)
  */
 #undef CONFIG_PARAVIRT
-#ifdef CONFIG_X86_32
-#define _ASM_X86_DESC_H 1
-#endif
+#undef CONFIG_PARAVIRT_SPINLOCKS

 #include <linux/linkage.h>
 #include <linux/screen_info.h>