Re: [PATCH] fix memory leak in mm/slab.c::alloc_kmemlist() (try #3)

Jesper Juhl
2006-03-22T00:53:46Z

Hi Pekka, Andrew, Christoph & everyone else,

On Monday 20 March 2006 09:55, Jesper Juhl wrote:
> Hi Pekka,
>
> On 3/19/06, Pekka Enberg <penberg@cs.helsinki.fi> wrote:
> > On 3/18/06, Jesper Juhl <jesper.juhl@gmail.com> wrote:
> > > Currently the only caller of alloc_kmemlist() will BUG() if alloc_kmemlist()
> > > fails, but that doesn't mean we shouldn't clean up properly IMHO. Also, the
> > > caller (do_tune_cpucache()) could maybe be changed in the future to do
> > > something more clever than just BUG() and in that case we really shouldn't
> > > be leaking memory when we return -ENOMEM.
> >
> > Yeah, and BUG() can be no-op for embedded.
> >
> > On 3/18/06, Jesper Juhl <jesper.juhl@gmail.com> wrote:
> > > The patch has been compile and boot tested on x86, but since I'm not very
> > > intimate with the slab code I'd appreciate it if someone would take a close
> > > look on the changes before merging them.
> >
> > You probably didn't hit the error path on your x86 box. The patch
> > looks good to me for -mm although there's few comments below.
> >
> > > +/*
> > > + If one or more allocations fail we need to undo all allocations done up to
> > > + this point.
> > > + Unfortunately this means yet another loop, but since this only happens on
> > > + failure and frees up memory in a memory-tight situation, it's not too bad.
> > > + */
> >
> > The formatting of this comment looks strange.
> >
> > > + for_each_online_node(node) {
> > > + if (count <= 0)
> > > + break;
> > > + if (cachep->nodelists[node]) {
> >
> > Would probably make sense to extract the above expression into local
> > variable to reduce kernel text size.
> >
> > > + kfree(cachep->nodelists[node]->shared);
> > > + free_alien_cache(cachep->nodelists[node]->alien);
> > > + kfree(cachep->nodelists[node]);
> > > + cachep->nodelists[node] = NULL;
> > > + }
> > > + count--;
> > > + }
> > > + return -ENOMEM;
> >
>
> Thank you very much for your feedback.
>
> I'll create an updated patch with the changes you suggest. They make
> perfect sense.
>

Here's the latest version of my patch to fix the mem leak in alloc_kmemlist().
It should address Pekkas's comments.

Andrew: Do you think this could go into -mm and get some field testing, so
perhaps it has a chance of making 2.6.17?

Fix memory leak in mm/slab.c::alloc_kmemlist().
If one allocation fails we have to roll-back all allocations made up to the
point of failure.

Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
---

mm/slab.c | 36 ++++++++++++++++++++++++++++++------
1 files changed, 30 insertions(+), 6 deletions(-)

--- linux-2.6.16-rc6-mm2-orig/mm/slab.c 2006-03-18 16:55:55.000000000 +0100
+++ linux-2.6.16-rc6-mm2/mm/slab.c 2006-03-21 22:33:45.000000000 +0100
@@ -3399,12 +3399,17 @@ EXPORT_SYMBOL_GPL(kmem_cache_name);
static int alloc_kmemlist(struct kmem_cache *cachep)
{
int node;
+ int count = -1;
struct kmem_list3 *l3;
- int err = 0;
+ struct array_cache *new;
+ struct array_cache **new_alien;

for_each_online_node(node) {
- struct array_cache *nc = NULL, *new;
- struct array_cache **new_alien = NULL;
+ struct array_cache *nc = NULL;
+
+ new = NULL;
+ new_alien = NULL;
+ count++;
#ifdef CONFIG_NUMA
new_alien = alloc_alien_cache(node, cachep->limit);
if (!new_alien)
@@ -3447,10 +3452,29 @@ static int alloc_kmemlist(struct kmem_ca
cachep->batchcount + cachep->num;
cachep->nodelists[node] = l3;
}
- return err;
+ return 0;
+/**
+ * If one or more allocations fail we need to undo all allocations done up to
+ * this point. Unfortunately this means yet another loop, but since this only
+ * happens on failure and frees up memory in a memory-tight situation, it's
+ * not too bad.
+ */
fail:
- err = -ENOMEM;
- return err;
+ kfree(new);
+ free_alien_cache(new_alien);
+ for_each_online_node(node) {
+ if (count <= 0)
+ break;
+ l3 = cachep->nodelists[node];
+ if (l3) {
+ kfree(l3->shared);
+ free_alien_cache(l3->alien);
+ kfree(l3);
+ cachep->nodelists[node] = NULL;
+ }
+ count--;
+ }
+ return -ENOMEM;
}

struct ccupdate_struct {