[RFC PATCH v2 6/9] fuse: take fuse connection generation into account

[Alexander Mikhalitsyn]

- modify dentry revalidation algorithm to check inode/connection
generations. If them are not equal then perform revalidation.

remark: during forced dentry revalidation we are sending FUSE_LOOKUP
request to the userspace daemon and if it return the same inode after
lookup then we can "upgrade" inode connection generation without
invalidating it.

- don't send FUSE_FSYNC, FUSE_RELEASE, etc requests to the userspace
daemon about stale inodes (this can confuse libfuse)

Cc: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Amir Goldstein <amir73il@xxxxxxxxx>
Cc: Stéphane Graber <stgraber@xxxxxxxxxx>
Cc: Seth Forshee <sforshee@xxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Andrei Vagin <avagin@xxxxxxxxx>
Cc: Pavel Tikhomirov <ptikhomirov@xxxxxxxxxxxxx>
Cc: Bernd Schubert <bschubert@xxxxxxx>
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: criu@xxxxxxxxxx
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
---
 fs/fuse/dir.c    |  4 +++-
 fs/fuse/file.c   | 13 ++++++++++---
 fs/fuse/fuse_i.h |  3 ++-
 fs/fuse/inode.c  |  2 +-
 4 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index bfbe59e8fce2..d0fdf7289d56 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -213,7 +213,8 @@ static int fuse_dentry_revalidate(struct dentry *entry, unsigned int flags)
 	inode = d_inode_rcu(entry);
 	if (inode && fuse_is_bad(inode))
 		goto invalid;
-	else if (time_before64(fuse_dentry_time(entry), get_jiffies_64()) ||
+	else if ((inode && fuse_stale_inode_conn(inode)) ||
+		 time_before64(fuse_dentry_time(entry), get_jiffies_64()) ||
 		 (flags & (LOOKUP_EXCL | LOOKUP_REVAL | LOOKUP_RENAME_TARGET))) {
 		struct fuse_entry_out outarg;
 		FUSE_ARGS(args);
@@ -255,6 +256,7 @@ static int fuse_dentry_revalidate(struct dentry *entry, unsigned int flags)
 			}
 			spin_lock(&fi->lock);
 			fi->nlookup++;
+			fi->conn_gen = READ_ONCE(get_fuse_conn(inode)->conn_gen);
 			spin_unlock(&fi->lock);
 		}
 		kfree(forget);
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 742f90b4e638..b977d087b925 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -111,8 +111,14 @@ static void fuse_file_put(struct fuse_file *ff, bool sync, bool isdir)
 	if (refcount_dec_and_test(&ff->count)) {
 		struct fuse_args *args = &ff->release_args->args;
 
-		if (isdir ? ff->fm->fc->flags.no_opendir : ff->fm->fc->flags.no_open) {
-			/* Do nothing when client does not implement 'open' */
+		if (fuse_stale_ff(ff) ||
+		    (isdir ? ff->fm->fc->flags.no_opendir : ff->fm->fc->flags.no_open)) {
+			/*
+			 * Do nothing when client does not implement 'open' OR
+			 * file descriptor was opened in the previous connection generation,
+			 * so, current daemon likely not aware of this FD, let's just skip
+			 * FUSE_RELEASE(DIR) request.
+			 */
 			fuse_release_end(ff->fm, args, 0);
 		} else if (sync) {
 			fuse_simple_request(ff->fm, args);
@@ -598,9 +604,10 @@ static int fuse_fsync(struct file *file, loff_t start, loff_t end,
 {
 	struct inode *inode = file->f_mapping->host;
 	struct fuse_conn *fc = get_fuse_conn(inode);
+	struct fuse_file *ff = file->private_data;
 	int err;
 
-	if (fuse_is_bad(inode))
+	if (fuse_stale_ff(ff) || fuse_is_bad(inode))
 		return -EIO;
 
 	inode_lock(inode);
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 943d5011dfa0..90c5b3459864 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -957,7 +957,8 @@ static inline bool fuse_stale_inode(const struct inode *inode, int generation,
 				    struct fuse_attr *attr)
 {
 	return inode->i_generation != generation ||
-		inode_wrong_type(inode, attr->mode);
+		inode_wrong_type(inode, attr->mode) ||
+		fuse_stale_inode_conn(inode);
 }
 
 static inline void fuse_make_bad(struct inode *inode)
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 389bea6e4a69..26a4149f6db7 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -124,7 +124,7 @@ static void fuse_evict_inode(struct inode *inode)
 			fuse_dax_inode_cleanup(inode);
 		if (fi->nlookup) {
 			fuse_queue_forget(fc, fi->forget, fi->nodeid,
-					  fi->nlookup, false);
+					  fi->nlookup, fuse_stale_inode_conn(inode));
 			fi->forget = NULL;
 		}
 	}
-- 
2.34.1