From 720abae3d68ae966044497dd9ee5ccf3b16e700c Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Thu, 5 Nov 2015 18:44:18 -0800 Subject: rcu: force alignment on struct callback_head/rcu_head Make struct callback_head aligned to size of pointer. On most architectures it happens naturally due ABI requirements, but some architectures (like CRIS) have weird ABI and we need to ask it explicitly. The alignment is required to guarantee that bits 0 and 1 of @next will be clear under normal conditions -- as long as we use call_rcu(), call_rcu_bh(), call_rcu_sched(), or call_srcu() to queue callback. This guarantee is important for few reasons: - future call_rcu_lazy() will make use of lower bits in the pointer; - the structure shares storage spacer in struct page with @compound_head, which encode PageTail() in bit 0. The guarantee is needed to avoid false-positive PageTail(). False postive PageTail() caused crash on crisv32[1]. It happend due misaligned task_struct->rcu, which was byte-aligned. [1] http://lkml.kernel.org/r/55FAEA67.9000102@roeck-us.net Signed-off-by: Kirill A. Shutemov Reported-by: Guenter Roeck Tested-by: Guenter Roeck Acked-by: Paul E. McKenney Cc: Mikael Starvik Cc: Jesper Nilsson Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/types.h | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) (limited to 'include/linux/types.h') diff --git a/include/linux/types.h b/include/linux/types.h index c314989d9158..70d8500bddf1 100644 --- a/include/linux/types.h +++ b/include/linux/types.h @@ -205,11 +205,25 @@ struct ustat { * struct callback_head - callback structure for use with RCU and task_work * @next: next update requests in a list * @func: actual update function to call after the grace period. + * + * The struct is aligned to size of pointer. On most architectures it happens + * naturally due ABI requirements, but some architectures (like CRIS) have + * weird ABI and we need to ask it explicitly. + * + * The alignment is required to guarantee that bits 0 and 1 of @next will be + * clear under normal conditions -- as long as we use call_rcu(), + * call_rcu_bh(), call_rcu_sched(), or call_srcu() to queue callback. + * + * This guarantee is important for few reasons: + * - future call_rcu_lazy() will make use of lower bits in the pointer; + * - the structure shares storage spacer in struct page with @compound_head, + * which encode PageTail() in bit 0. The guarantee is needed to avoid + * false-positive PageTail(). */ struct callback_head { struct callback_head *next; void (*func)(struct callback_head *head); -}; +} __attribute__((aligned(sizeof(void *)))); #define rcu_head callback_head typedef void (*rcu_callback_t)(struct rcu_head *head); -- cgit v1.2.3 From fbc416ff86183e2203cdf975e2881d7c164b0271 Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Fri, 20 Nov 2015 12:12:21 +0100 Subject: arm64: fix building without CONFIG_UID16 As reported by Michal Simek, building an ARM64 kernel with CONFIG_UID16 disabled currently fails because the system call table still needs to reference the individual function entry points that are provided by kernel/sys_ni.c in this case, and the declarations are hidden inside of #ifdef CONFIG_UID16: arch/arm64/include/asm/unistd32.h:57:8: error: 'sys_lchown16' undeclared here (not in a function) __SYSCALL(__NR_lchown, sys_lchown16) I believe this problem only exists on ARM64, because older architectures tend to not need declarations when their system call table is built in assembly code, while newer architectures tend to not need UID16 support. ARM64 only uses these system calls for compatibility with 32-bit ARM binaries. This changes the CONFIG_UID16 check into CONFIG_HAVE_UID16, which is set unconditionally on ARM64 with CONFIG_COMPAT, so we see the declarations whenever we need them, but otherwise the behavior is unchanged. Fixes: af1839eb4bd4 ("Kconfig: clean up the long arch list for the UID16 config option") Signed-off-by: Arnd Bergmann Acked-by: Will Deacon Cc: stable@vger.kernel.org Signed-off-by: Catalin Marinas --- include/linux/syscalls.h | 2 +- include/linux/types.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) (limited to 'include/linux/types.h') diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index a156b82dd14c..c2b66a277e98 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -524,7 +524,7 @@ asmlinkage long sys_chown(const char __user *filename, asmlinkage long sys_lchown(const char __user *filename, uid_t user, gid_t group); asmlinkage long sys_fchown(unsigned int fd, uid_t user, gid_t group); -#ifdef CONFIG_UID16 +#ifdef CONFIG_HAVE_UID16 asmlinkage long sys_chown16(const char __user *filename, old_uid_t user, old_gid_t group); asmlinkage long sys_lchown16(const char __user *filename, diff --git a/include/linux/types.h b/include/linux/types.h index 70d8500bddf1..70dd3dfde631 100644 --- a/include/linux/types.h +++ b/include/linux/types.h @@ -35,7 +35,7 @@ typedef __kernel_gid16_t gid16_t; typedef unsigned long uintptr_t; -#ifdef CONFIG_UID16 +#ifdef CONFIG_HAVE_UID16 /* This is defined by include/asm-{arch}/posix_types.h */ typedef __kernel_old_uid_t old_uid_t; typedef __kernel_old_gid_t old_gid_t; -- cgit v1.2.3