Patch "cred/userns: define current_user_ns() as a function" has been added to the 4.4-stable tree

Patch "cred/userns: define current_user_ns() as a function" has been added to the 4.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    cred/userns: define current_user_ns() as a function

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     cred-userns-define-current_user_ns-as-a-function.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 0335695dfa4df01edff5bb102b9a82a0668ee51e Mon Sep 17 00:00:00 2001
From: Arnd Bergmann <arnd@arndb.de>
Date: Tue, 22 Mar 2016 14:27:11 -0700
Subject: cred/userns: define current_user_ns() as a function

From: Arnd Bergmann <arnd@arndb.de>

commit 0335695dfa4df01edff5bb102b9a82a0668ee51e upstream.

The current_user_ns() macro currently returns &init_user_ns when user
namespaces are disabled, and that causes several warnings when building
with gcc-6.0 in code that compares the result of the macro to
&init_user_ns itself:

  fs/xfs/xfs_ioctl.c: In function 'xfs_ioctl_setattr_check_projid':
  fs/xfs/xfs_ioctl.c:1249:22: error: self-comparison always evaluates to true [-Werror=tautological-compare]
    if (current_user_ns() == &init_user_ns)

This is a legitimate warning in principle, but here it isn't really
helpful, so I'm reprasing the definition in a way that shuts up the
warning.  Apparently gcc only warns when comparing identical literals,
but it can figure out that the result of an inline function can be
identical to a constant expression in order to optimize a condition yet
not warn about the fact that the condition is known at compile time.
This is exactly what we want here, and it looks reasonable because we
generally prefer inline functions over macros anyway.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Yaowei Bai <baiyaowei@cmss.chinamobile.com>
Cc: James Morris <james.l.morris@oracle.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 include/linux/capability.h |    2 --
 include/linux/cred.h       |    5 ++++-
 2 files changed, 4 insertions(+), 3 deletions(-)

--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -40,8 +40,6 @@ struct inode;
 struct dentry;
 struct user_namespace;
 
-struct user_namespace *current_user_ns(void);
-
 extern const kernel_cap_t __cap_empty_set;
 extern const kernel_cap_t __cap_init_eff_set;
 
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -377,7 +377,10 @@ extern struct user_namespace init_user_n
 #ifdef CONFIG_USER_NS
 #define current_user_ns()	(current_cred_xxx(user_ns))
 #else
-#define current_user_ns()	(&init_user_ns)
+static inline struct user_namespace *current_user_ns(void)
+{
+	return &init_user_ns;
+}
 #endif
 
 


Patches currently in stable-queue which might be from arnd@arndb.de are

queue-4.4/net-vxge-avoid-unused-function-warnings.patch
queue-4.4/cred-userns-define-current_user_ns-as-a-function.patch
queue-4.4/stable-fixup-hotplug-fix-unused-function-warning.patch
queue-4.4/scsi-mvsas-fix-command_active-typo.patch
queue-4.4/staging-comedi-dt282x-tidy-up-register-bit-defines.patch