Date: Mon, 3 Mar 2003 16:20:22 +0000
From: Matthew Wilcox <willy@debian.org>
To: "Theodore Ts'o" <tytso@mit.edu>
Cc: Trivial Kernel Patches <trivial@rustcorp.com.au>,
       linux-kernel@vger.kernel.org
Subject: Stack usage in random.c
Message-ID: <20030303162022.I7301@parcelfarce.linux.theplanet.co.uk>
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Jeff Garzik whined about how much stack space was being used by
extract_entropy().  So I went and looked and reclaimed 352 bytes of stack.
Damn SHA ...

It's actually worse (better?) than that -- xfer_secondary_pool() can call
extract_entropy() again, so I may have saved over 700 bytes of stack
usage here.  It's safe for xfer_secondary_pool() to share its parent's
tmp because it hasn't been used at this point.

--- linux-2.5.63/drivers/char/random.c	2003-02-24 13:05:06.000000000 -0600
+++ linux-2.5.63-random/drivers/char/random.c	2003-03-03 08:05:24.000000000 -0600
@@ -1228,10 +1228,8 @@
  * at which point we do a "catastrophic reseeding".
  */
 static inline void xfer_secondary_pool(struct entropy_store *r,
-				       size_t nbytes)
+				       size_t nbytes, __u32 *tmp)
 {
-	__u32	tmp[TMP_BUF_SIZE];
-
 	if (r->entropy_count < nbytes * 8 &&
 	    r->entropy_count < r->poolinfo.POOLBITS) {
 		int nwords = min_t(int,
@@ -1284,7 +1282,7 @@
 		r->entropy_count = r->poolinfo.POOLBITS;
 
 	if (flags & EXTRACT_ENTROPY_SECONDARY)
-		xfer_secondary_pool(r, nbytes);
+		xfer_secondary_pool(r, nbytes, tmp);
 
 	DEBUG_ENT("%s has %d bits, want %d bits\n",
 		  r == sec_random_state ? "secondary" :

-- 
"It's not Hollywood.  War is real, war is primarily not about defeat or
victory, it is about death.  I've seen thousands and thousands of dead bodies.
Do you think I want to have an academic debate on this subject?" -- Robert Fisk
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