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Commit 99f1c013 authored by Oleg Drokin's avatar Oleg Drokin Committed by Greg Kroah-Hartman
Browse files

staging/lustre/llite: Close atomic_open race with several openers 



Right now, if it's an open of a negative dentry, a race is possible
with several openers who all try to instantiate/rehash the same
dentry and would hit a BUG_ON in d_add.
But in fact if we got a negative dentry in atomic_open, that means
we just revalidated it so no point in talking to MDS at all,
just return ENOENT and make the race go away completely.

Signed-off-by: default avatarOleg Drokin <green@linuxhacker.ru>
Cc: stable <stable@vger.kernel.org> # 4.7+
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 694d0d0b

drivers/staging/lustre/lustre/llite/namei.c

+24 −19
Original line number Diff line number Diff line
@@ -388,6 +388,7 @@ static int ll_lookup_it_finish(struct ptlrpc_request *request, 
	struct inode *inode = NULL;

	__u64 bits = 0;

	int rc = 0;

	struct dentry *alias;



	/* NB 1 request reference will be taken away by ll_intent_lock()

	 * when I return
@@ -412,26 +413,12 @@ static int ll_lookup_it_finish(struct ptlrpc_request *request, 
		 */

	}



	/* Only hash *de if it is unhashed (new dentry).

	 * Atoimc_open may passing hashed dentries for open.

	 */

	if (d_unhashed(*de)) {

		struct dentry *alias;



	alias = ll_splice_alias(inode, *de);

	if (IS_ERR(alias)) {

		rc = PTR_ERR(alias);

		goto out;

	}

	*de = alias;

	} else if (!it_disposition(it, DISP_LOOKUP_NEG)  &&

		   !it_disposition(it, DISP_OPEN_CREATE)) {

		/* With DISP_OPEN_CREATE dentry will be

		 * instantiated in ll_create_it.

		 */

		LASSERT(!d_inode(*de));

		d_instantiate(*de, inode);

	}



	if (!it_disposition(it, DISP_LOOKUP_NEG)) {

		/* we have lookup look - unhide dentry */
@@ -587,6 +574,24 @@ static int ll_atomic_open(struct inode *dir, struct dentry *dentry, 
	       dentry, PFID(ll_inode2fid(dir)), dir, file, open_flags, mode,

	       *opened);



	/* Only negative dentries enter here */

	LASSERT(!d_inode(dentry));



	if (!d_in_lookup(dentry)) {

		/* A valid negative dentry that just passed revalidation,

		 * there's little point to try and open it server-side,

		 * even though there's a minuscle chance it might succeed.

		 * Either way it's a valid race to just return -ENOENT here.

		 */

		if (!(open_flags & O_CREAT))

			return -ENOENT;



		/* Otherwise we just unhash it to be rehashed afresh via

		 * lookup if necessary

		 */

		d_drop(dentry);

	}



	it = kzalloc(sizeof(*it), GFP_NOFS);

	if (!it)

		return -ENOMEM;