From: Miklos Szeredi Date: Tue, 11 Apr 2006 05:54:55 +0000 (-0700) Subject: [PATCH] fuse: simplify locking X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=0720b315976447cba3f0c3e211223b8cb82b0f93;p=GitHub%2Fmt8127%2Fandroid_kernel_alcatel_ttab.git [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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c index 75c6e9166c39..c510533c6849 100644 --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -23,13 +23,11 @@ static kmem_cache_t *fuse_req_cachep; 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 @@ static ssize_t fuse_dev_readv(struct file *file, const struct iovec *iov, 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 @@ void fuse_abort_conn(struct fuse_conn *fc) 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); } diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c index 78700cbb9cdf..620579a69107 100644 --- a/fs/fuse/inode.c +++ b/fs/fuse/inode.c @@ -414,37 +414,6 @@ static struct fuse_conn *new_conn(void) return fc; } -static struct fuse_conn *get_conn(struct file *file, struct super_block *sb) -{ - struct fuse_conn *fc; - int err; - - err = -EINVAL; - if (file->f_op != &fuse_dev_operations) - goto out_err; - - err = -ENOMEM; - fc = new_conn(); - if (!fc) - goto out_err; - - spin_lock(&fuse_lock); - err = -EINVAL; - if (file->private_data) - goto out_unlock; - - kobject_get(&fc->kobj); - file->private_data = fc; - spin_unlock(&fuse_lock); - return fc; - - out_unlock: - spin_unlock(&fuse_lock); - kobject_put(&fc->kobj); - out_err: - return ERR_PTR(err); -} - static struct inode *get_root_inode(struct super_block *sb, unsigned mode) { struct fuse_attr attr; @@ -526,12 +495,9 @@ static void fuse_send_init(struct fuse_conn *fc) static unsigned long long conn_id(void) { + /* BKL is held for ->get_sb() */ static unsigned long long ctr = 1; - unsigned long long val; - spin_lock(&fuse_lock); - val = ctr++; - spin_unlock(&fuse_lock); - return val; + return ctr++; } static int fuse_fill_super(struct super_block *sb, void *data, int silent) @@ -556,10 +522,17 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent) if (!file) return -EINVAL; - fc = get_conn(file, sb); - fput(file); - if (IS_ERR(fc)) - return PTR_ERR(fc); + if (file->f_op != &fuse_dev_operations) + return -EINVAL; + + /* Setting file->private_data can't race with other mount() + instances, since BKL is held for ->get_sb() */ + if (file->private_data) + return -EINVAL; + + fc = new_conn(); + if (!fc) + return -ENOMEM; fc->flags = d.flags; fc->user_id = d.user_id; @@ -589,10 +562,16 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent) goto err_put_root; sb->s_root = root_dentry; - spin_lock(&fuse_lock); fc->mounted = 1; fc->connected = 1; - spin_unlock(&fuse_lock); + kobject_get(&fc->kobj); + file->private_data = fc; + /* + * atomic_dec_and_test() in fput() provides the necessary + * memory barrier for file->private_data to be visible on all + * CPUs after this + */ + fput(file); fuse_send_init(fc); @@ -601,6 +580,7 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent) err_put_root: dput(root_dentry); err: + fput(file); kobject_put(&fc->kobj); return err; }