Patch "cred/userns: define current_user_ns() as a function" has been added to the 3.18-stable tree

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 3.18-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-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Arnd Bergmann <[email protected]>
Date: Tue, 22 Mar 2016 14:27:11 -0700
Subject: cred/userns: define current_user_ns() as a function

From: Arnd Bergmann <[email protected]>

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.

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

@@ -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;
 

@@ -354,7 +354,10 @@ 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 [email protected] are

queue-3.18/ib-iser-fix-sparse-warnings.patch queue-3.18/cred-userns-define-current_user_ns-as-a-function.patch queue-3.18/pci-xilinx-fix-harmless-format-string-warning.patch queue-3.18/alsa-ppc-awacs-shut-up-maybe-uninitialized-warning.patch queue-3.18/net-tg3-avoid-uninitialized-variable-warning.patch queue-3.18/mtd-avoid-stack-overflow-in-mtd-cfi-code.patch queue-3.18/powerpc-ptrace-fix-out-of-bounds-array-access-warning.patch queue-3.18/mlx5-avoid-build-warnings-on-32-bit.patch queue-3.18/drbd-avoid-redefinition-of-bits_per_page.patch