linux-kernel - [PATCH 2/3] execve: improve interactivity with large arguments

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Message-Id: <20100908023628.A1F5A401AF@magilla.sf.frob.com>
Date:	Tue,  7 Sep 2010 19:36:28 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	linux-kernel@...r.kernel.org, oss-security@...ts.openwall.com,
	Solar Designer <solar@...nwall.com>,
	Kees Cook <kees.cook@...onical.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Neil Horman <nhorman@...driver.com>,
	linux-fsdevel@...r.kernel.org, pageexec@...email.hu,
	"Brad Spengler <spender@...ecurity.net> Eugene Teo" 
	<eugene@...hat.com>
Subject: [PATCH 2/3] execve: improve interactivity with large arguments

This adds a preemption point during the copying of the argument and
environment strings for execve, in copy_strings().  There is already
a preemption point in the count() loop, so this doesn't add any new
points in the abstract sense.

When the total argument+environment strings are very large, the time
spent copying them can be much more than a normal user time slice.
So this change improves the interactivity of the rest of the system
when one process is doing an execve with very large arguments.

Signed-off-by: Roland McGrath <roland@...hat.com>
---
 fs/exec.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 1b63237..6f2d777 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -419,6 +419,8 @@ static int copy_strings(int argc, const char __user *const __user *argv,
 		while (len > 0) {
 			int offset, bytes_to_copy;
 
+			cond_resched();
+
 			offset = pos % PAGE_SIZE;
 			if (offset == 0)
 				offset = PAGE_SIZE;
--
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