Remove zpl_revalidate

This patch removes the need for zpl_revalidate altogether.

There were 3 main reasons why we used d_revalidate:

1. periodic automounted snapshots umount deferral
2. negative dentries created before snapshot rollback
3. stale inodes referenced by dentry cache after snapshot rollback

Periodic snapshots deferral solution introduces zfs_exit_fs function,
which is called as a part of ZFS_EXIT(zfsvfs_t) macro.

Negative dentries and stale inodes are solved by flushing the dcache
for the particular dataset on zfs_resume_fs call.

This patch also removes now unused HAVE_S_D_OP configure test.

Reviewed-by: Aleksa Sarai <cyphar@cyphar.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Pavel Snajdr <snajpa@snajpa.net>
Closes openzfs#8774 
Closes openzfs#9549

config/kernel-dentry-operations.m4

@@ -150,37 +150,13 @@ AC_DEFUN([ZFS_AC_KERNEL_CONST_DENTRY_OPERATIONS], [
 	])
 ])
 
-dnl #
-dnl # 2.6.38 API change
-dnl # Added sb->s_d_op default dentry_operations member
-dnl #
-AC_DEFUN([ZFS_AC_KERNEL_SRC_S_D_OP], [
-	ZFS_LINUX_TEST_SRC([super_block_s_d_op], [
-		#include <linux/fs.h>
-	],[
-		struct super_block sb __attribute__ ((unused));
-		sb.s_d_op = NULL;
-	])
-])
-
-AC_DEFUN([ZFS_AC_KERNEL_S_D_OP], [
-	AC_MSG_CHECKING([whether super_block has s_d_op])
-	ZFS_LINUX_TEST_RESULT([super_block_s_d_op], [
-		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_S_D_OP, 1, [struct super_block has s_d_op])
-	], [
-		AC_MSG_RESULT(no)
-	])
-])
-
 AC_DEFUN([ZFS_AC_KERNEL_SRC_DENTRY], [
         ZFS_AC_KERNEL_SRC_D_MAKE_ROOT
         ZFS_AC_KERNEL_SRC_D_OBTAIN_ALIAS
         ZFS_AC_KERNEL_SRC_D_PRUNE_ALIASES
         ZFS_AC_KERNEL_SRC_D_SET_D_OP
         ZFS_AC_KERNEL_SRC_D_REVALIDATE_NAMEIDATA
         ZFS_AC_KERNEL_SRC_CONST_DENTRY_OPERATIONS
-        ZFS_AC_KERNEL_SRC_S_D_OP
 ])
 
 AC_DEFUN([ZFS_AC_KERNEL_DENTRY], [
@@ -190,5 +166,4 @@ AC_DEFUN([ZFS_AC_KERNEL_DENTRY], [
         ZFS_AC_KERNEL_D_SET_D_OP
         ZFS_AC_KERNEL_D_REVALIDATE_NAMEIDATA
         ZFS_AC_KERNEL_CONST_DENTRY_OPERATIONS
-        ZFS_AC_KERNEL_S_D_OP
 ])

include/os/linux/zfs/sys/zfs_vfsops.h

@@ -197,6 +197,7 @@ typedef struct zfid_long {
 extern int zfs_suspend_fs(zfsvfs_t *zfsvfs);
 extern int zfs_resume_fs(zfsvfs_t *zfsvfs, struct dsl_dataset *ds);
 extern int zfs_end_fs(zfsvfs_t *zfsvfs, struct dsl_dataset *ds);
+extern void zfs_exit_fs(zfsvfs_t *zfsvfs);
 extern int zfs_userspace_one(zfsvfs_t *zfsvfs, zfs_userquota_prop_t type,
     const char *domain, uint64_t rid, uint64_t *valuep);
 extern int zfs_userspace_many(zfsvfs_t *zfsvfs, zfs_userquota_prop_t type,

include/os/linux/zfs/sys/zfs_znode_impl.h

@@ -84,6 +84,7 @@ do {								\
 /* Must be called before exiting the operation. */
 #define	ZFS_EXIT(zfsvfs)					\
 do {								\
+	zfs_exit_fs(zfsvfs);					\
 	rrm_exit(&(zfsvfs)->z_teardown_lock, FTAG);		\
 } while (0)
 #define	ZPL_EXIT(zfsvfs)	ZFS_EXIT(zfsvfs)

include/os/linux/zfs/sys/zpl.h

@@ -45,7 +45,6 @@ extern const struct inode_operations zpl_inode_operations;
 extern const struct inode_operations zpl_dir_inode_operations;
 extern const struct inode_operations zpl_symlink_inode_operations;
 extern const struct inode_operations zpl_special_inode_operations;
-extern dentry_operations_t zpl_dentry_operations;
 
 /* zpl_file.c */
 extern ssize_t zpl_read_common(struct inode *ip, const char *buf,

module/os/linux/zfs/zfs_vfsops.c

@@ -1931,9 +1931,6 @@ zfs_domount(struct super_block *sb, zfs_mnt_t *zm, int silent)
 	sb->s_op = &zpl_super_operations;
 	sb->s_xattr = zpl_xattr_handlers;
 	sb->s_export_op = &zpl_export_operations;
-#ifdef HAVE_S_D_OP
-	sb->s_d_op = &zpl_dentry_operations;
-#endif /* HAVE_S_D_OP */
 
 	/* Set features for file system. */
 	zfs_set_fuid_feature(zfsvfs);
@@ -2303,6 +2300,16 @@ zfs_resume_fs(zfsvfs_t *zfsvfs, dsl_dataset_t *ds)
 		zfs_unlinked_drain(zfsvfs);
 	}
 
+	/*
+	 * Most of the time zfs_suspend_fs is used for changing the contents
+	 * of the underlying dataset. ZFS rollback and receive operations
+	 * might create files for which negative dentries are present in
+	 * the cache. Since walking the dcache would require a lot of GPL-only
+	 * code duplication, it's much easier on these rather rare occasions
+	 * just to flush the whole dcache for the given dataset/filesystem.
+	 */
+	shrink_dcache_sb(zfsvfs->z_sb);
+
 bail:
 	if (err != 0)
 		zfsvfs->z_unmounted = B_TRUE;
@@ -2353,6 +2360,26 @@ zfs_end_fs(zfsvfs_t *zfsvfs, dsl_dataset_t *ds)
 	return (0);
 }
 
+/*
+ * Automounted snapshots rely on periodic revalidation
+ * to defer snapshots from being automatically unmounted.
+ */
+
+inline void
+zfs_exit_fs(zfsvfs_t *zfsvfs)
+{
+	if (!zfsvfs->z_issnap)
+		return;
+
+	if (time_after(jiffies, zfsvfs->z_snap_defer_time +
+	    MAX(zfs_expire_snapshot * HZ / 2, HZ))) {
+		zfsvfs->z_snap_defer_time = jiffies;
+		zfsctl_snapshot_unmount_delay(zfsvfs->z_os->os_spa,
+		    dmu_objset_id(zfsvfs->z_os),
+		    zfs_expire_snapshot);
+	}
+}
+
 int
 zfs_set_version(zfsvfs_t *zfsvfs, uint64_t newvers)
 {

module/os/linux/zfs/zpl_inode.c

@@ -70,9 +70,6 @@ zpl_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
 
 	spin_lock(&dentry->d_lock);
 	dentry->d_time = jiffies;
-#ifndef HAVE_S_D_OP
-	d_set_d_op(dentry, &zpl_dentry_operations);
-#endif /* HAVE_S_D_OP */
 	spin_unlock(&dentry->d_lock);
 
 	if (error) {
@@ -655,59 +652,6 @@ zpl_fallocate(struct inode *ip, int mode, loff_t offset, loff_t len)
 }
 #endif /* HAVE_INODE_FALLOCATE */
 
-static int
-#ifdef HAVE_D_REVALIDATE_NAMEIDATA
-zpl_revalidate(struct dentry *dentry, struct nameidata *nd)
-{
-	unsigned int flags = (nd ? nd->flags : 0);
-#else
-zpl_revalidate(struct dentry *dentry, unsigned int flags)
-{
-#endif /* HAVE_D_REVALIDATE_NAMEIDATA */
-	/* CSTYLED */
-	zfsvfs_t *zfsvfs = dentry->d_sb->s_fs_info;
-	int error;
-
-	if (flags & LOOKUP_RCU)
-		return (-ECHILD);
-
-	/*
-	 * Automounted snapshots rely on periodic dentry revalidation
-	 * to defer snapshots from being automatically unmounted.
-	 */
-	if (zfsvfs->z_issnap) {
-		if (time_after(jiffies, zfsvfs->z_snap_defer_time +
-		    MAX(zfs_expire_snapshot * HZ / 2, HZ))) {
-			zfsvfs->z_snap_defer_time = jiffies;
-			zfsctl_snapshot_unmount_delay(zfsvfs->z_os->os_spa,
-			    dmu_objset_id(zfsvfs->z_os), zfs_expire_snapshot);
-		}
-	}
-
-	/*
-	 * After a rollback negative dentries created before the rollback
-	 * time must be invalidated.  Otherwise they can obscure files which
-	 * are only present in the rolled back dataset.
-	 */
-	if (dentry->d_inode == NULL) {
-		spin_lock(&dentry->d_lock);
-		error = time_before(dentry->d_time, zfsvfs->z_rollback_time);
-		spin_unlock(&dentry->d_lock);
-
-		if (error)
-			return (0);
-	}
-
-	/*
-	 * The dentry may reference a stale inode if a mounted file system
-	 * was rolled back to a point in time where the object didn't exist.
-	 */
-	if (dentry->d_inode && ITOZ(dentry->d_inode)->z_is_stale)
-		return (0);
-
-	return (1);
-}
-
 const struct inode_operations zpl_inode_operations = {
 	.setattr	= zpl_setattr,
 	.getattr	= zpl_getattr,
@@ -820,7 +764,3 @@ const struct inode_operations zpl_special_inode_operations = {
 #endif /* HAVE_GET_ACL | HAVE_CHECK_ACL | HAVE_PERMISSION */
 #endif /* CONFIG_FS_POSIX_ACL */
 };
-
-dentry_operations_t zpl_dentry_operations = {
-	.d_revalidate	= zpl_revalidate,
-};