Commit b0841eef authored by Al Viro's avatar Al Viro Committed by Christoph Hellwig
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configfs: provide exclusion between IO and removals 



Make sure that attribute methods are not called after the item
has been removed from the tree.  To do so, we
	* at the point of no return in removals, grab ->frag_sem
exclusive and mark the fragment dead.
	* call the methods of attributes with ->frag_sem taken
shared and only after having verified that the fragment is still
alive.

	The main benefit is for method instances - they are
guaranteed that the objects they are accessing *and* all ancestors
are still there.  Another win is that we don't need to bother
with extra refcount on config_item when opening a file -
the item will be alive for as long as it stays in the tree, and
we won't touch it/attributes/any associated data after it's
been removed from the tree.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
parent 47320fbe

fs/configfs/dir.c

+23 −0
Original line number Diff line number Diff line
@@ -1461,6 +1461,7 @@ static int configfs_rmdir(struct inode *dir, struct dentry *dentry) 
	struct config_item *item;

	struct configfs_subsystem *subsys;

	struct configfs_dirent *sd;

	struct configfs_fragment *frag;

	struct module *subsys_owner = NULL, *dead_item_owner = NULL;

	int ret;
@@ -1518,6 +1519,16 @@ static int configfs_rmdir(struct inode *dir, struct dentry *dentry) 
		}

	} while (ret == -EAGAIN);



	frag = sd->s_frag;

	if (down_write_killable(&frag->frag_sem)) {

		spin_lock(&configfs_dirent_lock);

		configfs_detach_rollback(dentry);

		spin_unlock(&configfs_dirent_lock);

		return -EINTR;

	}

	frag->frag_dead = true;

	up_write(&frag->frag_sem);



	/* Get a working ref for the duration of this function */

	item = configfs_get_config_item(dentry);
@@ -1821,6 +1832,12 @@ void configfs_unregister_group(struct config_group *group) 
	struct configfs_subsystem *subsys = group->cg_subsys;

	struct dentry *dentry = group->cg_item.ci_dentry;

	struct dentry *parent = group->cg_item.ci_parent->ci_dentry;

	struct configfs_dirent *sd = dentry->d_fsdata;

	struct configfs_fragment *frag = sd->s_frag;



	down_write(&frag->frag_sem);

	frag->frag_dead = true;

	up_write(&frag->frag_sem);



	inode_lock_nested(d_inode(parent), I_MUTEX_PARENT);

	spin_lock(&configfs_dirent_lock);
@@ -1947,12 +1964,18 @@ void configfs_unregister_subsystem(struct configfs_subsystem *subsys) 
	struct config_group *group = &subsys->su_group;

	struct dentry *dentry = group->cg_item.ci_dentry;

	struct dentry *root = dentry->d_sb->s_root;

	struct configfs_dirent *sd = dentry->d_fsdata;

	struct configfs_fragment *frag = sd->s_frag;



	if (dentry->d_parent != root) {

		pr_err("Tried to unregister non-subsystem!\n");

		return;

	}



	down_write(&frag->frag_sem);

	frag->frag_dead = true;

	up_write(&frag->frag_sem);



	inode_lock_nested(d_inode(root),

			  I_MUTEX_PARENT);

	inode_lock_nested(d_inode(dentry), I_MUTEX_CHILD);

fs/configfs/file.c

+57 −18
Original line number Diff line number Diff line
@@ -48,22 +48,32 @@ struct configfs_buffer { 
	};

};



static inline struct configfs_fragment *to_frag(struct file *file)

{

	struct configfs_dirent *sd = file->f_path.dentry->d_fsdata;



	return sd->s_frag;

}



static int fill_read_buffer(struct configfs_buffer * buffer)

static int fill_read_buffer(struct file *file, struct configfs_buffer *buffer)

{

	ssize_t count;

	struct configfs_fragment *frag = to_frag(file);

	ssize_t count = -ENOENT;



	if (!buffer->page)

		buffer->page = (char *) get_zeroed_page(GFP_KERNEL);

	if (!buffer->page)

		return -ENOMEM;



	down_read(&frag->frag_sem);

	if (!frag->frag_dead)

		count = buffer->attr->show(buffer->item, buffer->page);

	up_read(&frag->frag_sem);



	if (count < 0)

		return count;

	if (WARN_ON_ONCE(count > (ssize_t)SIMPLE_ATTR_SIZE))

		return -EIO;



	buffer->needs_read_fill = 0;

	buffer->count = count;

	return 0;
@@ -96,7 +106,7 @@ configfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *pp 


	mutex_lock(&buffer->mutex);

	if (buffer->needs_read_fill) {

		retval = fill_read_buffer(buffer);

		retval = fill_read_buffer(file, buffer);

		if (retval)

			goto out;

	}
@@ -133,6 +143,7 @@ static ssize_t 
configfs_read_bin_file(struct file *file, char __user *buf,

		       size_t count, loff_t *ppos)

{

	struct configfs_fragment *frag = to_frag(file);

	struct configfs_buffer *buffer = file->private_data;

	ssize_t retval = 0;

	ssize_t len = min_t(size_t, count, PAGE_SIZE);
@@ -148,7 +159,12 @@ configfs_read_bin_file(struct file *file, char __user *buf, 


	if (buffer->needs_read_fill) {

		/* perform first read with buf == NULL to get extent */

		down_read(&frag->frag_sem);

		if (!frag->frag_dead)

			len = buffer->bin_attr->read(buffer->item, NULL, 0);

		else

			len = -ENOENT;

		up_read(&frag->frag_sem);

		if (len <= 0) {

			retval = len;

			goto out;
@@ -168,8 +184,13 @@ configfs_read_bin_file(struct file *file, char __user *buf, 
		buffer->bin_buffer_size = len;



		/* perform second read to fill buffer */

		down_read(&frag->frag_sem);

		if (!frag->frag_dead)

			len = buffer->bin_attr->read(buffer->item,

						     buffer->bin_buffer, len);

		else

			len = -ENOENT;

		up_read(&frag->frag_sem);

		if (len < 0) {

			retval = len;

			vfree(buffer->bin_buffer);
@@ -220,9 +241,16 @@ fill_write_buffer(struct configfs_buffer * buffer, const char __user * buf, size 
}



static int

flush_write_buffer(struct configfs_buffer *buffer, size_t count)

flush_write_buffer(struct file *file, struct configfs_buffer *buffer, size_t count)

{

	return buffer->attr->store(buffer->item, buffer->page, count);

	struct configfs_fragment *frag = to_frag(file);

	int res = -ENOENT;



	down_read(&frag->frag_sem);

	if (!frag->frag_dead)

		res = buffer->attr->store(buffer->item, buffer->page, count);

	up_read(&frag->frag_sem);

	return res;

}
@@ -252,7 +280,7 @@ configfs_write_file(struct file *file, const char __user *buf, size_t count, lof 
	mutex_lock(&buffer->mutex);

	len = fill_write_buffer(buffer, buf, count);

	if (len > 0)

		len = flush_write_buffer(buffer, len);

		len = flush_write_buffer(file, buffer, len);

	if (len > 0)

		*ppos += len;

	mutex_unlock(&buffer->mutex);
@@ -328,6 +356,7 @@ out: 
static int __configfs_open_file(struct inode *inode, struct file *file, int type)

{

	struct dentry *dentry = file->f_path.dentry;

	struct configfs_fragment *frag = to_frag(file);

	struct configfs_attribute *attr;

	struct configfs_buffer *buffer;

	int error;
@@ -337,8 +366,13 @@ static int __configfs_open_file(struct inode *inode, struct file *file, int type 
	if (!buffer)

		goto out;



	error = -ENOENT;

	down_read(&frag->frag_sem);

	if (unlikely(frag->frag_dead))

		goto out_free_buffer;



	error = -EINVAL;

	buffer->item = configfs_get_config_item(dentry->d_parent);

	buffer->item = to_item(dentry->d_parent);

	if (!buffer->item)

		goto out_free_buffer;
@@ -396,6 +430,7 @@ static int __configfs_open_file(struct inode *inode, struct file *file, int type 
	buffer->read_in_progress = false;

	buffer->write_in_progress = false;

	file->private_data = buffer;

	up_read(&frag->frag_sem);

	return 0;



out_put_module:
@@ -403,6 +438,7 @@ out_put_module: 
out_put_item:

	config_item_put(buffer->item);

out_free_buffer:

	up_read(&frag->frag_sem);

	kfree(buffer);

out:

	return error;
@@ -412,8 +448,6 @@ static int configfs_release(struct inode *inode, struct file *filp) 
{

	struct configfs_buffer *buffer = filp->private_data;



	if (buffer->item)

		config_item_put(buffer->item);

	module_put(buffer->owner);

	if (buffer->page)

		free_page((unsigned long)buffer->page);
@@ -439,12 +473,17 @@ static int configfs_release_bin_file(struct inode *inode, struct file *file) 
	buffer->read_in_progress = false;



	if (buffer->write_in_progress) {

		struct configfs_fragment *frag = to_frag(file);

		buffer->write_in_progress = false;



		down_read(&frag->frag_sem);

		if (!frag->frag_dead) {

			/* result of ->release() is ignored */

		buffer->bin_attr->write(buffer->item, buffer->bin_buffer,

			buffer->bin_attr->write(buffer->item,

					buffer->bin_buffer,

					buffer->bin_buffer_size);



		}

		up_read(&frag->frag_sem);

		/* vfree on NULL is safe */

		vfree(buffer->bin_buffer);

		buffer->bin_buffer = NULL;

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