[PATCH] fuse: simplify locking
This is in preparation for removing the global spinlock in favor of a
per-mount one.
The only critical part is the interaction between fuse_dev_release() and
fuse_fill_super(): fuse_dev_release() must see the assignment to
file->private_data, otherwise it will leak the reference to fuse_conn.
This is ensured by the fput() operation, which will synchronize the assignment
with other CPU's that may do a final fput() soon after this.
Also redundant locking is removed from fuse_fill_super(), where exclusion is
already ensured by the BKL held for this function by the VFS.
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 75c6e91..c510533 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -23,13 +23,11 @@
static struct fuse_conn *fuse_get_conn(struct file *file)
{
- struct fuse_conn *fc;
- spin_lock(&fuse_lock);
- fc = file->private_data;
- if (fc && !fc->connected)
- fc = NULL;
- spin_unlock(&fuse_lock);
- return fc;
+ /*
+ * Lockless access is OK, because file->private data is set
+ * once during mount and is valid until the file is released.
+ */
+ return file->private_data;
}
static void fuse_request_init(struct fuse_req *req)
@@ -607,19 +605,16 @@
unsigned long nr_segs, loff_t *off)
{
int err;
- struct fuse_conn *fc;
struct fuse_req *req;
struct fuse_in *in;
struct fuse_copy_state cs;
unsigned reqsize;
+ struct fuse_conn *fc = fuse_get_conn(file);
+ if (!fc)
+ return -EPERM;
restart:
spin_lock(&fuse_lock);
- fc = file->private_data;
- err = -EPERM;
- if (!fc)
- goto err_unlock;
-
err = -EAGAIN;
if ((file->f_flags & O_NONBLOCK) && fc->connected &&
list_empty(&fc->pending))
@@ -915,17 +910,13 @@
static int fuse_dev_release(struct inode *inode, struct file *file)
{
- struct fuse_conn *fc;
-
- spin_lock(&fuse_lock);
- fc = file->private_data;
+ struct fuse_conn *fc = fuse_get_conn(file);
if (fc) {
+ spin_lock(&fuse_lock);
fc->connected = 0;
end_requests(fc, &fc->pending);
end_requests(fc, &fc->processing);
- }
- spin_unlock(&fuse_lock);
- if (fc) {
+ spin_unlock(&fuse_lock);
fasync_helper(-1, file, 0, &fc->fasync);
kobject_put(&fc->kobj);
}