Merge branch 'locking-rwsem-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull support for killable rwsems from Ingo Molnar:
 "This, by Michal Hocko, implements down_write_killable().

  The main usecase will be to update mm_sem usage sites to use this new
  API, to allow the mm-reaper introduced in commit aac453635549 ("mm,
  oom: introduce oom reaper") to tear down oom victim address spaces
  asynchronously with minimum latencies and without deadlock worries"

[ The vfs will want it too as the inode lock is changed from a mutex to
  a rwsem due to the parallel lookup and readdir updates ]

* 'locking-rwsem-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  locking/rwsem: Fix comment on register clobbering
  locking/rwsem: Fix down_write_killable()
  locking/rwsem, x86: Add frame annotation for call_rwsem_down_write_failed_killable()
  locking/rwsem: Provide down_write_killable()
  locking/rwsem, x86: Provide __down_write_killable()
  locking/rwsem, s390: Provide __down_write_killable()
  locking/rwsem, ia64: Provide __down_write_killable()
  locking/rwsem, alpha: Provide __down_write_killable()
  locking/rwsem: Introduce basis for down_write_killable()
  locking/rwsem, sparc: Drop superfluous arch specific implementation
  locking/rwsem, sh: Drop superfluous arch specific implementation
  locking/rwsem, xtensa: Drop superfluous arch specific implementation
  locking/rwsem: Drop explicit memory barriers
  locking/rwsem: Get rid of __down_write_nested()

2 files changed, 40 insertions, 18 deletions

diff --git a/arch/x86/include/asm/rwsem.h b/arch/x86/include/asm/rwsem.h
index ceec86eb68e9..453744c1d347 100644
--- a/arch/x86/include/asm/rwsem.h
+++ b/arch/x86/include/asm/rwsem.h
@@ -99,26 +99,36 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
 /*
  * lock for writing
  */
-static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
+#define ____down_write(sem, slow_path)			\
+({							\
+	long tmp;					\
+	struct rw_semaphore* ret;			\
+	asm volatile("# beginning down_write\n\t"	\
+		     LOCK_PREFIX "  xadd      %1,(%3)\n\t"	\
+		     /* adds 0xffff0001, returns the old value */ \
+		     "  test " __ASM_SEL(%w1,%k1) "," __ASM_SEL(%w1,%k1) "\n\t" \
+		     /* was the active mask 0 before? */\
+		     "  jz        1f\n"			\
+		     "  call " slow_path "\n"		\
+		     "1:\n"				\
+		     "# ending down_write"		\
+		     : "+m" (sem->count), "=d" (tmp), "=a" (ret)	\
+		     : "a" (sem), "1" (RWSEM_ACTIVE_WRITE_BIAS) \
+		     : "memory", "cc");			\
+	ret;						\
+})
+
+static inline void __down_write(struct rw_semaphore *sem)
 {
-	long tmp;
-	asm volatile("# beginning down_write\n\t"
-		     LOCK_PREFIX "  xadd      %1,(%2)\n\t"
-		     /* adds 0xffff0001, returns the old value */
-		     "  test " __ASM_SEL(%w1,%k1) "," __ASM_SEL(%w1,%k1) "\n\t"
-		     /* was the active mask 0 before? */
-		     "  jz        1f\n"
-		     "  call call_rwsem_down_write_failed\n"
-		     "1:\n"
-		     "# ending down_write"
-		     : "+m" (sem->count), "=d" (tmp)
-		     : "a" (sem), "1" (RWSEM_ACTIVE_WRITE_BIAS)
-		     : "memory", "cc");
+	____down_write(sem, "call_rwsem_down_write_failed");
 }
 
-static inline void __down_write(struct rw_semaphore *sem)
+static inline int __down_write_killable(struct rw_semaphore *sem)
 {
-	__down_write_nested(sem, 0);
+	if (IS_ERR(____down_write(sem, "call_rwsem_down_write_failed_killable")))
+		return -EINTR;
+
+	return 0;
 }
 
 /*
diff --git a/arch/x86/lib/rwsem.S b/arch/x86/lib/rwsem.S
index be110efa0096..bf2c6074efd2 100644
--- a/arch/x86/lib/rwsem.S
+++ b/arch/x86/lib/rwsem.S
@@ -29,8 +29,10 @@
  * there is contention on the semaphore.
  *
  * %eax contains the semaphore pointer on entry. Save the C-clobbered
- * registers (%eax, %edx and %ecx) except %eax whish is either a return
- * value or just clobbered..
+ * registers (%eax, %edx and %ecx) except %eax which is either a return
+ * value or just gets clobbered. Same is true for %edx so make sure GCC
+ * reloads it after the slow path, by making it hold a temporary, for
+ * example see ____down_write().
  */
 
 #define save_common_regs \
@@ -106,6 +108,16 @@ ENTRY(call_rwsem_down_write_failed)
 	ret
 ENDPROC(call_rwsem_down_write_failed)
 
+ENTRY(call_rwsem_down_write_failed_killable)
+	FRAME_BEGIN
+	save_common_regs
+	movq %rax,%rdi
+	call rwsem_down_write_failed_killable
+	restore_common_regs
+	FRAME_END
+	ret
+ENDPROC(call_rwsem_down_write_failed_killable)
+
 ENTRY(call_rwsem_wake)
 	FRAME_BEGIN
 	/* do nothing if still outstanding active readers */