Re: [PATCH] cpuset: make ntasks to be a monotonic increasing value

Paul Jackson
2008-07-31T12:24:17Z

I agree that in theory, this kernel/cpuset.c update_tasks_nodemask()
loop could loop forever, and that by forcing ntasks to keep increasing
monotonically, this guarantees that it cannot loop forever.

I also agree that no known exploit of this exists, and doubt that
any could be created.

I did find the added code logic to be a tad more difficult to read
than I'd like. How about the following patch, instead:

---
kernel/cpuset.c | 3 +++
1 file changed, 3 insertions(+)

--- 2.6.25-mm1.orig/kernel/cpuset.c 2008-07-31 07:05:23.000000000 -0500
+++ 2.6.25-mm1/kernel/cpuset.c 2008-07-31 07:13:48.000000000 -0500
@@ -880,6 +880,7 @@ static int update_nodemask(struct cpuset
struct task_struct *p;
struct mm_struct **mmarray;
int i, n, ntasks;
+ int prev_ntasks = 0;
int migrate;
int fudge;
int retval;
@@ -939,7 +940,9 @@ static int update_nodemask(struct cpuset
*/
while (1) {
ntasks = cgroup_task_count(cs->css.cgroup); /* guess */
+ ntasks = max(ntasks, prev_ntasks); /* keep increasing */
ntasks += fudge;
+ prev_ntasks = ntasks;
mmarray = kmalloc(ntasks * sizeof(*mmarray), GFP_KERNEL);
if (!mmarray)
goto done;

--
I won't rest till it's the best ...
Programmer, Linux Scalability
Paul Jackson <pj@sgi.com> 1.940.382.4214