mm: add ksys_fadvise64_64() helper; remove in-kernel call to sys_fadvise64_64()

Using the ksys_fadvise64_64() helper allows us to avoid the in-kernel
calls to the sys_fadvise64_64() syscall. The ksys_ prefix denotes that
this function is meant as a drop-in replacement for the syscall. In
particular, it uses the same calling convention as ksys_fadvise64_64().

Some compat stubs called sys_fadvise64(), which then just passed through
the arguments to sys_fadvise64_64(). Get rid of this indirection, and call
ksys_fadvise64_64() directly.

This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.net

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>

arch/arm/kernel/sys_arm.c

@@ -35,5 +35,5 @@
 asmlinkage long sys_arm_fadvise64_64(int fd, int advice,
 				     loff_t offset, loff_t len)
 {
-	return sys_fadvise64_64(fd, offset, len, advice);
+	return ksys_fadvise64_64(fd, offset, len, advice);
 }

arch/mips/kernel/linux32.c

@@ -149,7 +149,7 @@ asmlinkage long sys32_fadvise64_64(int fd, int __pad,
 	unsigned long a4, unsigned long a5,
 	int flags)
 {
-	return sys_fadvise64_64(fd,
+	return ksys_fadvise64_64(fd,
 			merge_64(a2, a3), merge_64(a4, a5),
 			flags);
 }

arch/parisc/kernel/sys_parisc.c

@@ -352,7 +352,7 @@ asmlinkage long parisc_fadvise64_64(int fd,
 			unsigned int high_off, unsigned int low_off,
 			unsigned int high_len, unsigned int low_len, int advice)
 {
-	return sys_fadvise64_64(fd, (loff_t)high_off << 32 | low_off,
+	return ksys_fadvise64_64(fd, (loff_t)high_off << 32 | low_off,
 			(loff_t)high_len << 32 | low_len, advice);
 }
 

arch/powerpc/kernel/sys_ppc32.c

@@ -113,7 +113,7 @@ asmlinkage int compat_sys_ftruncate64(unsigned int fd, u32 reg4, unsigned long h
 long ppc32_fadvise64(int fd, u32 unused, u32 offset_high, u32 offset_low,
 		     size_t len, int advice)
 {
-	return sys_fadvise64(fd, (u64)offset_high << 32 | offset_low, len,
+	return ksys_fadvise64_64(fd, (u64)offset_high << 32 | offset_low, len,
 				 advice);
 }
 

arch/powerpc/kernel/syscalls.c

@@ -119,7 +119,7 @@ long ppc64_personality(unsigned long personality)
 long ppc_fadvise64_64(int fd, int advice, u32 offset_high, u32 offset_low,
 		      u32 len_high, u32 len_low)
 {
-	return sys_fadvise64(fd, (u64)offset_high << 32 | offset_low,
+	return ksys_fadvise64_64(fd, (u64)offset_high << 32 | offset_low,
 				 (u64)len_high << 32 | len_low, advice);
 }
 

arch/s390/kernel/compat_linux.c

@@ -483,7 +483,8 @@ COMPAT_SYSCALL_DEFINE5(s390_fadvise64, int, fd, u32, high, u32, low, compat_size
 		advise = POSIX_FADV_DONTNEED;
 	else if (advise == 5)
 		advise = POSIX_FADV_NOREUSE;
-	return sys_fadvise64(fd, (unsigned long)high << 32 | low, len, advise);
+	return ksys_fadvise64_64(fd, (unsigned long)high << 32 | low, len,
+				 advise);
 }
 
 struct fadvise64_64_args {
@@ -503,7 +504,7 @@ COMPAT_SYSCALL_DEFINE1(s390_fadvise64_64, struct fadvise64_64_args __user *, arg
 		a.advice = POSIX_FADV_DONTNEED;
 	else if (a.advice == 5)
 		a.advice = POSIX_FADV_NOREUSE;
-	return sys_fadvise64_64(a.fd, a.offset, a.len, a.advice);
+	return ksys_fadvise64_64(a.fd, a.offset, a.len, a.advice);
 }
 
 COMPAT_SYSCALL_DEFINE6(s390_sync_file_range, int, fd, u32, offhigh, u32, offlow,

arch/sh/kernel/sys_sh32.c

@@ -52,10 +52,10 @@ asmlinkage int sys_fadvise64_64_wrapper(int fd, u32 offset0, u32 offset1,
 				u32 len0, u32 len1, int advice)
 {
 #ifdef  __LITTLE_ENDIAN__
-	return sys_fadvise64_64(fd, (u64)offset1 << 32 | offset0,
+	return ksys_fadvise64_64(fd, (u64)offset1 << 32 | offset0,
 				 (u64)len1 << 32 | len0, advice);
 #else
-	return sys_fadvise64_64(fd, (u64)offset0 << 32 | offset1,
+	return ksys_fadvise64_64(fd, (u64)offset0 << 32 | offset1,
 				 (u64)len0 << 32 | len1, advice);
 #endif
 }

arch/sparc/kernel/sys_sparc32.c

@@ -225,7 +225,7 @@ long compat_sys_fadvise64(int fd,
 			  unsigned long offlo,
 			  compat_size_t len, int advice)
 {
-	return sys_fadvise64_64(fd, (offhi << 32) | offlo, len, advice);
+	return ksys_fadvise64_64(fd, (offhi << 32) | offlo, len, advice);
 }
 
 long compat_sys_fadvise64_64(int fd,
@@ -233,7 +233,7 @@ long compat_sys_fadvise64_64(int fd,
 			     unsigned long lenhi, unsigned long lenlo,
 			     int advice)
 {
-	return sys_fadvise64_64(fd,
+	return ksys_fadvise64_64(fd,
 				 (offhi << 32) | offlo,
 				 (lenhi << 32) | lenlo,
 				 advice);

arch/x86/ia32/sys_ia32.c

@@ -194,7 +194,7 @@ COMPAT_SYSCALL_DEFINE6(x86_fadvise64_64, int, fd, __u32, offset_low,
 		       __u32, offset_high, __u32, len_low, __u32, len_high,
 		       int, advice)
 {
-	return sys_fadvise64_64(fd,
+	return ksys_fadvise64_64(fd,
 				 (((u64)offset_high)<<32) | offset_low,
 				 (((u64)len_high)<<32) | len_low,
 				 advice);
@@ -218,7 +218,7 @@ COMPAT_SYSCALL_DEFINE6(x86_sync_file_range, int, fd, unsigned int, off_low,
 COMPAT_SYSCALL_DEFINE5(x86_fadvise64, int, fd, unsigned int, offset_lo,
 		       unsigned int, offset_hi, size_t, len, int, advice)
 {
-	return sys_fadvise64_64(fd, ((u64)offset_hi << 32) | offset_lo,
+	return ksys_fadvise64_64(fd, ((u64)offset_hi << 32) | offset_lo,
 				 len, advice);
 }
 

arch/xtensa/kernel/syscall.c

@@ -55,7 +55,7 @@ asmlinkage long xtensa_shmat(int shmid, char __user *shmaddr, int shmflg)
 asmlinkage long xtensa_fadvise64_64(int fd, int advice,
 		unsigned long long offset, unsigned long long len)
 {
-	return sys_fadvise64_64(fd, offset, len, advice);
+	return ksys_fadvise64_64(fd, offset, len, advice);
 }
 
 #ifdef CONFIG_MMU

include/linux/syscalls.h

@@ -970,6 +970,15 @@ ssize_t ksys_pread64(unsigned int fd, char __user *buf, size_t count,
 ssize_t ksys_pwrite64(unsigned int fd, const char __user *buf,
 		      size_t count, loff_t pos);
 int ksys_fallocate(int fd, int mode, loff_t offset, loff_t len);
+#ifdef CONFIG_ADVISE_SYSCALLS
+int ksys_fadvise64_64(int fd, loff_t offset, loff_t len, int advice);
+#else
+static inline int ksys_fadvise64_64(int fd, loff_t offset, loff_t len,
+				    int advice)
+{
+	return -EINVAL;
+}
+#endif
 
 /*
  * The following kernel syscall equivalents are just wrappers to fs-internal

mm/fadvise.c

@@ -26,7 +26,8 @@
  * POSIX_FADV_WILLNEED could set PG_Referenced, and POSIX_FADV_NOREUSE could
  * deactivate the pages and clear PG_Referenced.
  */
-SYSCALL_DEFINE4(fadvise64_64, int, fd, loff_t, offset, loff_t, len, int, advice)
+
+int ksys_fadvise64_64(int fd, loff_t offset, loff_t len, int advice)
 {
 	struct fd f = fdget(fd);
 	struct inode *inode;
@@ -185,11 +186,16 @@ out:
 	return ret;
 }
 
+SYSCALL_DEFINE4(fadvise64_64, int, fd, loff_t, offset, loff_t, len, int, advice)
+{
+	return ksys_fadvise64_64(fd, offset, len, advice);
+}
+
 #ifdef __ARCH_WANT_SYS_FADVISE64
 
 SYSCALL_DEFINE4(fadvise64, int, fd, loff_t, offset, size_t, len, int, advice)
 {
-	return sys_fadvise64_64(fd, offset, len, advice);
+	return ksys_fadvise64_64(fd, offset, len, advice);
 }
 
 #endif