Re: [PATCH linux-next] SUNRPC: rpcrdma_register_default_external: Dynamically allocate ib_phys_buf

rpcrdma_register_default_external() is several frames into
the call stack which goes deeper yet. You run the risk of stack
corruption by declaring such a large automatic variable,
so dynamically allocate the array of 'struct ib_phys_buf' objects in
order to silence the frame-larger-than warning.

net/sunrpc/xprtrdma/verbs.c: In function 'rpcrdma_register_default_external':
net/sunrpc/xprtrdma/verbs.c:1774:1: warning: the frame size of 1056 bytes is larger than 1024 bytes [-Wframe-larger-than=]

gcc version 4.6.3

Cc: Trond Myklebust <redacted>
Cc: "J. Bruce Fields" <redacted>
Cc: "David S. Miller" <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>
Cc: Tom Tucker <tom-/Yg/VP3ZvrM@public.gmane.org>
Cc: Haggai Eran <haggaie-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
Cc: Or Gerlitz <ogerlitz-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
Cc: Shani Michaeli <shanim-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
Cc: linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Cc: netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Signed-off-by: Tim Gardner <redacted>
---
  net/sunrpc/xprtrdma/verbs.c |    7 ++++++-
  1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index 93726560..0916467 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c

@@ -1736,9 +1736,13 @@ rpcrdma_register_default_external(struct rpcrdma_mr_seg *seg,
  	int mem_priv = (writing ? IB_ACCESS_REMOTE_WRITE :
  				  IB_ACCESS_REMOTE_READ);
  	struct rpcrdma_mr_seg *seg1 = seg;
-	struct ib_phys_buf ipb[RPCRDMA_MAX_DATA_SEGS];
+	struct ib_phys_buf *ipb;
  	int len, i, rc = 0;
  
+	ipb = kmalloc(sizeof(*ipb) * RPCRDMA_MAX_DATA_SEGS, GFP_KERNEL);
+	if (!ipb)
+		return -ENOMEM;
+
  	if (*nsegs > RPCRDMA_MAX_DATA_SEGS)
  		*nsegs = RPCRDMA_MAX_DATA_SEGS;
  	for (len = 0, i = 0; i < *nsegs;) {

@@ -1770,6 +1774,7 @@ rpcrdma_register_default_external(struct rpcrdma_mr_seg *seg,
  		seg1->mr_len = len;
  	}
  	*nsegs = i;
+	kfree(ipb);
  	return rc;
  }