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Subject[PATCH linux-next v2] lockd: nlmclnt_reclaim(): avoid stack overflow
Date
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@netapp.com>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Cc: linux-nfs@vger.kernel.org
Signed-off-by: Tim Gardner <tim.gardner@canonical.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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