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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: Oleg Drokin <green@linuxhacker.ru>
Cc: stable <stable@vger.kernel.org> # 4.7+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Oleg Drokin 2016-07-14 23:40:21 -04:00 committed by Greg Kroah-Hartman
parent 694d0d0bb2
commit 99f1c01319
1 changed files with 24 additions and 19 deletions
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43
drivers/staging/lustre/lustre/llite/namei.c
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@ -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);
alias = ll_splice_alias(inode, *de);
if (IS_ERR(alias)) {
rc = PTR_ERR(alias);
goto out;
}
*de = alias;
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;