From 99f1c013194e64d4b67d5d318148303b0e1585e1 Mon Sep 17 00:00:00 2001 From: Oleg Drokin Date: Thu, 14 Jul 2016 23:40:21 -0400 Subject: [PATCH] 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 Cc: stable # 4.7+ Signed-off-by: Greg Kroah-Hartman --- drivers/staging/lustre/lustre/llite/namei.c | 43 ++++++++++++--------- 1 file changed, 24 insertions(+), 19 deletions(-) diff --git a/drivers/staging/lustre/lustre/llite/namei.c b/drivers/staging/lustre/lustre/llite/namei.c index 3664bfd0178b..2c4dc69731e8 100644 --- a/drivers/staging/lustre/lustre/llite/namei.c +++ b/drivers/staging/lustre/lustre/llite/namei.c @@ -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; -- 2.20.1