Linux 4.7 compat: inode_lock() and friends

Linux 4.7 changes i_mutex to i_rwsem, and we should used inode_lock and
inode_lock_shared to do exclusive and shared lock respectively.

We use spl_inode_lock{,_shared}() to hide the difference. Note that on older
kernel you'll always take an exclusive lock.

We also add all other inode_lock friends. And nested users now should
explicitly call spl_inode_lock_nested with correct subclass.

Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue openzfs/zfs#4665
Closes #549

config/spl-build.m4

@@ -45,6 +45,7 @@ AC_DEFUN([SPL_AC_CONFIG_KERNEL], [
 	SPL_AC_KMEM_CACHE_ALLOCFLAGS
 	SPL_AC_WAIT_ON_BIT
 	SPL_AC_MUTEX_OWNER
+	SPL_AC_INODE_LOCK
 ])
 
 AC_DEFUN([SPL_AC_MODULE_SYMVERS], [
@@ -1476,3 +1477,27 @@ AC_DEFUN([SPL_AC_MUTEX_OWNER], [
 	])
 	EXTRA_KCFLAGS="$tmp_flags"
 ])
+
+dnl #
+dnl # 4.7 API change
+dnl # i_mutex is changed to i_rwsem. Instead of directly using
+dnl # i_mutex/i_rwsem, we should use inode_lock() and inode_lock_shared()
+dnl # We test inode_lock_shared because inode_lock is introduced earlier.
+dnl #
+AC_DEFUN([SPL_AC_INODE_LOCK], [
+	AC_MSG_CHECKING([whether inode_lock_shared() exists])
+	tmp_flags="$EXTRA_KCFLAGS"
+	EXTRA_KCFLAGS="-Werror"
+	SPL_LINUX_TRY_COMPILE([
+		#include <linux/fs.h>
+	],[
+		struct inode *inode = NULL;
+		inode_lock_shared(inode);
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_INODE_LOCK_SHARED, 1, [yes])
+	],[
+		AC_MSG_RESULT(no)
+	])
+	EXTRA_KCFLAGS="$tmp_flags"
+])

include/linux/file_compat.h

@@ -76,8 +76,25 @@ spl_filp_fallocate(struct file *fp, int mode, loff_t offset, loff_t len)
 #define	spl_filp_fsync(fp, sync)	vfs_fsync(fp, (fp)->f_dentry, sync)
 #endif /* HAVE_2ARGS_VFS_FSYNC */
 
-#define	spl_inode_lock(ip)		mutex_lock_nested(&(ip)->i_mutex, I_MUTEX_PARENT)
+#ifdef HAVE_INODE_LOCK_SHARED
+#define	spl_inode_lock(ip)		inode_lock(ip)
+#define	spl_inode_unlock(ip)		inode_unlock(ip)
+#define	spl_inode_lock_shared(ip)	inode_lock_shared(ip)
+#define	spl_inode_unlock_shared(ip)	inode_unlock_shared(ip)
+#define	spl_inode_trylock(ip)		inode_trylock(ip)
+#define	spl_inode_trylock_shared(ip)	inode_trylock_shared(ip)
+#define	spl_inode_is_locked(ip)		inode_is_locked(ip)
+#define	spl_inode_lock_nested(ip, s)	inode_lock_nested(ip, s)
+#else
+#define	spl_inode_lock(ip)		mutex_lock(&(ip)->i_mutex)
 #define	spl_inode_unlock(ip)		mutex_unlock(&(ip)->i_mutex)
+#define	spl_inode_lock_shared(ip)	mutex_lock(&(ip)->i_mutex)
+#define	spl_inode_unlock_shared(ip)	mutex_unlock(&(ip)->i_mutex)
+#define	spl_inode_trylock(ip)		mutex_trylock(&(ip)->i_mutex)
+#define	spl_inode_trylock_shared(ip)	mutex_trylock(&(ip)->i_mutex)
+#define	spl_inode_is_locked(ip)		mutex_is_locked(&(ip)->i_mutex)
+#define	spl_inode_lock_nested(ip, s)	mutex_lock_nested(&(ip)->i_mutex, s)
+#endif
 
 #endif /* SPL_FILE_COMPAT_H */
 

module/spl/spl-vnode.c

@@ -352,7 +352,8 @@ spl_kern_path_locked(const char *name, struct path *path)
 	if (rc)
 		return (ERR_PTR(rc));
 
-	spl_inode_lock(parent.dentry->d_inode);
+	/* use I_MUTEX_PARENT because vfs_unlink needs it */
+	spl_inode_lock_nested(parent.dentry->d_inode, I_MUTEX_PARENT);
 
 	dentry = lookup_one_len(basename, parent.dentry, len);
 	if (IS_ERR(dentry)) {