[PATCH 1/1] fuse: add fuse_d_iput to postponed the iput

[Ed Tsai <ed.tsai@xxxxxxxxxxxx>]

When all the references of an inode are dropped, and write of its dirty
pages is serving in Daemon, reclaim may deadlock on a regular allocation
in Daemon.

Add fuse_dentry_iput and some FI_* flags to postponed the iput for the
inodes be using in fuse_write_inode.

Signed-off-by: Ed Tsai <ed.tsai@xxxxxxxxxxxx>
---
Hi Miklos,
I define d_iput for fuse to postpone the iput until the fuse_write_inode
is done. This works fine at our platform. Please help to check this.

 fs/fuse/dir.c    | 17 +++++++++++++++++
 fs/fuse/file.c   | 15 +++++++++++++++
 fs/fuse/fuse_i.h |  4 ++++
 3 files changed, 36 insertions(+)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 74303d6e987b..37d768088c87 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -331,6 +331,22 @@ static struct vfsmount *fuse_dentry_automount(struct path *path)
 	return mnt;
 }
 
+static void fuse_dentry_iput(struct dentry *dentry, struct inode *inode)
+{
+	struct fuse_inode *fi = get_fuse_inode(inode);
+	int need_iput = true;
+
+	spin_lock(&fi->lock);
+	if (test_bit(FUSE_I_WRITING, &fi->state)) {
+		set_bit(FUSE_I_NEED_IPUT, &fi->state);
+		need_iput = false;
+	}
+	spin_unlock(&fi->lock);
+
+	if (need_iput)
+		iput(inode);
+}
+
 const struct dentry_operations fuse_dentry_operations = {
 	.d_revalidate	= fuse_dentry_revalidate,
 	.d_delete	= fuse_dentry_delete,
@@ -339,6 +355,7 @@ const struct dentry_operations fuse_dentry_operations = {
 	.d_release	= fuse_dentry_release,
 #endif
 	.d_automount	= fuse_dentry_automount,
+	.d_iput		= fuse_dentry_iput,
 };
 
 const struct dentry_operations fuse_root_dentry_operations = {
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 05caa2b9272e..a291784d42bc 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1848,6 +1848,7 @@ int fuse_write_inode(struct inode *inode, struct writeback_control *wbc)
 {
 	struct fuse_inode *fi = get_fuse_inode(inode);
 	struct fuse_file *ff;
+	int need_iput = false;
 	int err;
 
 	/*
@@ -1862,10 +1863,24 @@ int fuse_write_inode(struct inode *inode, struct writeback_control *wbc)
 	WARN_ON(wbc->for_reclaim);
 
 	ff = __fuse_write_file_get(fi);
+
+	spin_lock(&fi->lock);
+	set_bit(FUSE_I_WRITING, &fi->state);
+	spin_unlock(&fi->lock);
+
 	err = fuse_flush_times(inode, ff);
 	if (ff)
 		fuse_file_put(ff, false, false);
 
+	spin_lock(&fi->lock);
+	clear_bit(FUSE_I_WRITING, &fi->state);
+	if (test_and_clear_bit(FUSE_I_NEED_IPUT, &fi->state))
+		need_iput = true;
+	spin_unlock(&fi->lock);
+
+	if (need_iput)
+		iput(inode);
+
 	return err;
 }
 
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 488b460e046f..f5851e5397ce 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -167,6 +167,10 @@ enum {
 	FUSE_I_SIZE_UNSTABLE,
 	/* Bad inode */
 	FUSE_I_BAD,
+	/* inode is writing */
+	FUSE_I_WRITING,
+	/* inode need iput() after writing */
+	FUSE_I_NEED_IPUT,
 };
 
 struct fuse_conn;
-- 
2.18.0