From ddfde6814073a136584aa06d4a3fce5fbb518fb0 Mon Sep 17 00:00:00 2001
From: Nick Craig-Wood <nick@craig-wood.com>
Date: Wed, 8 Jul 2020 10:27:26 +0100
Subject: [PATCH] vfs: fix directory locking caused by slow directory listings

Before this fix we took the directory lock to read the ModTime of the
directory. This was causing locking on directories which were being
re-read from the backend.

This commit gives the modtime its own lock so it can be read even when
the directory is being updated.

See: https://forum.rclone.org/t/high-cpu-load-with-rclone-mount/17604
---
 vfs/dir.go | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/vfs/dir.go b/vfs/dir.go
index a6889eb4c..972f75b23 100644
--- a/vfs/dir.go
+++ b/vfs/dir.go
@@ -29,12 +29,14 @@ type Dir struct {
 	mu      sync.RWMutex // protects the following
 	parent  *Dir         // parent, nil for root
 	path    string
-	modTime time.Time
 	entry   fs.Directory
 	read    time.Time         // time directory entry last read
 	items   map[string]Node   // directory entries - can be empty but not nil
 	virtual map[string]vState // virtual directory entries - may be nil
 	sys     atomic.Value      // user defined info to be attached here
+
+	modTimeMu sync.Mutex // protects the following
+	modTime   time.Time
 }
 
 //go:generate stringer -type=vState
@@ -270,11 +272,13 @@ func (d *Dir) _age(when time.Time) (age time.Duration, stale bool) {
 // reading everything again
 func (d *Dir) rename(newParent *Dir, fsDir fs.Directory) {
 	d.ForgetAll()
+	d.modTimeMu.Lock()
+	d.modTime = fsDir.ModTime(context.TODO())
+	d.modTimeMu.Unlock()
 	d.mu.Lock()
 	d.parent = newParent
 	d.entry = fsDir
 	d.path = fsDir.Remote()
-	d.modTime = fsDir.ModTime(context.TODO())
 	d.read = time.Time{}
 	d.mu.Unlock()
 }
@@ -550,8 +554,8 @@ func (d *Dir) isEmpty() (bool, error) {
 
 // ModTime returns the modification time of the directory
 func (d *Dir) ModTime() time.Time {
-	d.mu.RLock()
-	defer d.mu.RUnlock()
+	d.modTimeMu.Lock()
+	defer d.modTimeMu.Unlock()
 	// fs.Debugf(d.path, "Dir.ModTime %v", d.modTime)
 	return d.modTime
 }
@@ -566,9 +570,9 @@ func (d *Dir) SetModTime(modTime time.Time) error {
 	if d.vfs.Opt.ReadOnly {
 		return EROFS
 	}
-	d.mu.Lock()
+	d.modTimeMu.Lock()
 	d.modTime = modTime
-	d.mu.Unlock()
+	d.modTimeMu.Unlock()
 	return nil
 }