linux-kernel - [PATCH linux-next v2] lockd: nlmclnt

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Date:	Wed, 13 Feb 2013 08:40:16 -0700
From:	Tim Gardner <tim.gardner@...onical.com>
To:	linux-kernel@...r.kernel.org
Cc:	Tim Gardner <tim.gardner@...onical.com>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	"J. Bruce Fields" <bfields@...ldses.org>, linux-nfs@...r.kernel.org
Subject: [PATCH linux-next v2] lockd: nlmclnt_reclaim(): avoid stack overflow

Even though nlmclnt_reclaim() is only one call into the stack frame,
928 bytes on the stack seems like a lot. Recode to dynamically
allocate the request structure once from within the reclaimer task,
then pass this pointer into nlmclnt_reclaim() for reuse on
subsequent calls.

smatch analysis:

fs/lockd/clntproc.c:620 nlmclnt_reclaim() warn: 'reqst' puts
 928 bytes on stack

Also remove redundant assignment of 0 after memset.

Cc: Trond Myklebust <Trond.Myklebust@...app.com>
Cc: "J. Bruce Fields" <bfields@...ldses.org>
Cc: linux-nfs@...r.kernel.org
Signed-off-by: Tim Gardner <tim.gardner@...onical.com>
---

Changes from v1 -- don't return -ENOMEM from a task thread because it is
not propagated to the task creator. Instead print an error message and return.

 fs/lockd/clntlock.c         |   12 +++++++++++-
 fs/lockd/clntproc.c         |    6 ++----
 include/linux/lockd/lockd.h |    3 ++-
 3 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/fs/lockd/clntlock.c b/fs/lockd/clntlock.c
index 4885b53..6cd673d 100644
--- a/fs/lockd/clntlock.c
+++ b/fs/lockd/clntlock.c
@@ -220,10 +220,19 @@ reclaimer(void *ptr)
 {
 	struct nlm_host	  *host = (struct nlm_host *) ptr;
 	struct nlm_wait	  *block;
+	struct nlm_rqst   *req;
 	struct file_lock *fl, *next;
 	u32 nsmstate;
 	struct net *net = host->net;
 
+	req = kmalloc(sizeof(*req), GFP_KERNEL);
+	if (!req) {
+		printk(KERN_ERR "lockd: reclaimer unable to alloc memory."
+				" Locks for %s won't be reclaimed!\n",
+				host->h_name);
+		return 0;
+	}
+
 	allow_signal(SIGKILL);
 
 	down_write(&host->h_rwsem);
@@ -253,7 +262,7 @@ restart:
 		 */
 		if (signalled())
 			continue;
-		if (nlmclnt_reclaim(host, fl) != 0)
+		if (nlmclnt_reclaim(host, fl, req) != 0)
 			continue;
 		list_add_tail(&fl->fl_u.nfs_fl.list, &host->h_granted);
 		if (host->h_nsmstate != nsmstate) {
@@ -279,5 +288,6 @@ restart:
 	/* Release host handle after use */
 	nlmclnt_release_host(host);
 	lockd_down(net);
+	kfree(req);
 	return 0;
 }
diff --git a/fs/lockd/clntproc.c b/fs/lockd/clntproc.c
index 54f9e6c..b43114c 100644
--- a/fs/lockd/clntproc.c
+++ b/fs/lockd/clntproc.c
@@ -615,17 +615,15 @@ out_unlock:
  * RECLAIM: Try to reclaim a lock
  */
 int
-nlmclnt_reclaim(struct nlm_host *host, struct file_lock *fl)
+nlmclnt_reclaim(struct nlm_host *host, struct file_lock *fl,
+		struct nlm_rqst *req)
 {
-	struct nlm_rqst reqst, *req;
 	int		status;
 
-	req = &reqst;
 	memset(req, 0, sizeof(*req));
 	locks_init_lock(&req->a_args.lock.fl);
 	locks_init_lock(&req->a_res.lock.fl);
 	req->a_host  = host;
-	req->a_flags = 0;
 
 	/* Set up the argument struct */
 	nlmclnt_setlockargs(req, fl);
diff --git a/include/linux/lockd/lockd.h b/include/linux/lockd/lockd.h
index f5a051a..a395f1e 100644
--- a/include/linux/lockd/lockd.h
+++ b/include/linux/lockd/lockd.h
@@ -212,7 +212,8 @@ int		  nlmclnt_block(struct nlm_wait *block, struct nlm_rqst *req, long timeout)
 __be32		  nlmclnt_grant(const struct sockaddr *addr,
 				const struct nlm_lock *lock);
 void		  nlmclnt_recovery(struct nlm_host *);
-int		  nlmclnt_reclaim(struct nlm_host *, struct file_lock *);
+int		  nlmclnt_reclaim(struct nlm_host *, struct file_lock *,
+				  struct nlm_rqst *);
 void		  nlmclnt_next_cookie(struct nlm_cookie *);
 
 /*
-- 
1.7.9.5

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