[Devel] [PATCH hci-8.1 1/3] fs/fuse: give num_openers and i_size_unstable each a single role

[Liu Kui <kui.liu@virtuozzo.com>]

Currently fi->num_openers serves two purposes: it helps decide whether
the i_size attribute needs to be taken from the server, and it manages
when kio's file_open/file_close methods need to be called. The former
role already requires the extra i_size_unstable flag to handle lease
revokes, which makes num_openers redundant for that purpose.

Give each field a single role: use i_size_unstable as the "take the
attributes from the server" flag, and make num_openers a pure open
count managing the calls of kio's file_open/file_close. A new inode
starts with the i_size_unstable flag set, an open finding it set
refreshes the attributes and clears it on success, and the last
release sets it back after writeback has drained.

Also fix a bug where a failed refresh could re-trust stale local
attributes.

https://virtuozzo.atlassian.net/browse/VSTOR-147878

Signed-off-by: Liu Kui <kui.liu@virtuozzo.com>
---
 fs/fuse/file.c   | 21 ++++++++++++++++-----
 fs/fuse/fuse_i.h |  4 ++--
 fs/fuse/inode.c  |  5 +++--
 3 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index e0efb524cda7..c41d6445c7e5 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -293,8 +293,14 @@ static int fuse_open_close_wait(struct inode *inode, struct file *file)
 		inode_lock(inode);
 	spin_lock(&fi->lock);
 
-	if (++fi->num_openers == 1 || fi->i_size_unstable) {
-		fi->i_size_unstable = 1;
+	fi->num_openers++;
+	/*
+	 * i_size_unstable set means the attributes must be taken from the
+	 * server: no open has refreshed them yet (first open), the last
+	 * opener is gone, or the files were invalidated by a lease revoke.
+	 * Refresh the attributes so ours can be trusted again.
+	 */
+	if (fi->i_size_unstable) {
 		fi->inval_mask = ~0;
 		spin_unlock(&fi->lock);
 		err = fuse_update_attributes(inode, file, ~0);
@@ -303,9 +309,10 @@ static int fuse_open_close_wait(struct inode *inode, struct file *file)
 			err = fc->kio.op->file_open(file, inode);
 
 		spin_lock(&fi->lock);
-		fi->i_size_unstable = 0;
 		if (err)
 			fi->num_openers--;
+		else
+			fi->i_size_unstable = 0;
 	}
 
 	file->f_mode |= FMODE_NOWAIT;
@@ -583,8 +590,12 @@ static int fuse_release(struct inode *inode, struct file *file)
 			wait_event(fi->page_waitq, refcount_read(&ff->count) == 1);
 
 		spin_lock(&fi->lock);
-		/* since now we can trust userspace attr.size */
-		fi->num_openers--;
+		/*
+		 * Last opener is gone and its writeback has drained: from
+		 * now on take the attributes from the server again.
+		 */
+		if (--fi->num_openers == 0)
+			fi->i_size_unstable = 1;
 		spin_unlock(&fi->lock);
 	} else if (fc->close_wait)
 		wait_event(fi->page_waitq, refcount_read(&ff->count) == 1);
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 21f873337627..f6da643b9c86 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -200,10 +200,10 @@ struct fuse_inode {
 	/** Reference to backing file in passthrough mode */
 	struct fuse_backing *fb;
 #endif
-	/** Mostly to detect very first open */
+	/** Number of opens, drives kio file_open/file_close pairing */
 	int num_openers;
 
-	/** Even though num_openers>0, trust server i_size */
+	/** Take attributes (i_size) from the server, don't trust ours */
 	int i_size_unstable;
 
 	/** Private kdirect io context */
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index eb2e9a4f8756..4eaa89d9c46c 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -116,7 +116,8 @@ static struct inode *fuse_alloc_inode(struct super_block *sb)
 	fi->orig_ino = 0;
 	fi->state = 0;
 	fi->submount_lookup = NULL;
-	fi->i_size_unstable = 0;
+	/* take attributes from the server until the first open */
+	fi->i_size_unstable = 1;
 	fi->private = NULL;
 	fi->inval_files_seq = 0;
 	INIT_LIST_HEAD(&fi->rw_files);
@@ -328,7 +329,7 @@ u32 fuse_get_cache_mask(struct inode *inode)
 	if (fc->close_wait) {
 		struct fuse_inode *fi = get_fuse_inode(inode);
 
-		if (!fi->num_openers || fi->i_size_unstable)
+		if (fi->i_size_unstable)
 			return 0;
 	}
 

-- 
Git-155)

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