On Thu, 30 Jan 2014 13:14:46 -0800 (PST) David Rientjes <rientjes@xxxxxxxxxx> wrote:
> On Thu, 30 Jan 2014, Andrew Morton wrote:
>
> > Well gee, how did that one get through?
> >
> > What was the point in permanently allocating tmp_name, btw? "This
> > static temporary buffer is used to prevent from pointless shortliving
> > allocation"? That's daft - memcg_create_kmem_cache() is not a fastpath
> > and there are a million places in the kernel where we could permanently
> > leak memory because it is "pointless" to allocate on demand.
> >
> > The allocation of PATH_MAX bytes is unfortunate - kasprintf() wouild
> > work well here, but cgroup_name()'s need for rcu_read_lock() screws us
> > up.
> >
>
> What's funnier is that tmp_name isn't required at all since
> kmem_cache_create_memcg() is just going to do a kstrdup() on it anyway, so
> you could easily just pass in the pointer to memory that has been
> allocated for s->name rather than allocating memory twice.
We need a buffer to sprintf() into.
> > --- a/mm/memcontrol.c~mm-memcontrolc-memcg_create_kmem_cache-tweaks
> > +++ a/mm/memcontrol.c
> > @@ -3401,17 +3401,14 @@ static struct kmem_cache *memcg_create_k
> > struct kmem_cache *s)
> > {
> > struct kmem_cache *new = NULL;
> > - static char *tmp_name = NULL;
> > + static char *tmp_name;
>
> You're keeping it static and the mutex so you're still keeping it global,
> ok...
oop, I forgot to remove the `static'.
And I suppose the mutex now doesn't do anything, so...
From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Subject: mm/memcontrol.c: memcg_create_kmem_cache() tweaks
Allocate tmp_name on demand rather than permanently consuming PATH_MAX
bytes of memory. Remove the mutex which protected the static tmp_name.
Cc: Glauber Costa <glommer@xxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 23 ++++++++---------------
1 file changed, 8 insertions(+), 15 deletions(-)
diff -puN mm/memcontrol.c~mm-memcontrolc-memcg_create_kmem_cache-tweaks mm/memcontrol.c
--- a/mm/memcontrol.c~mm-memcontrolc-memcg_create_kmem_cache-tweaks
+++ a/mm/memcontrol.c
@@ -3400,24 +3400,18 @@ void mem_cgroup_destroy_cache(struct kme
static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
struct kmem_cache *s)
{
- struct kmem_cache *new = NULL;
- static char *tmp_name = NULL;
- static DEFINE_MUTEX(mutex); /* protects tmp_name */
+ struct kmem_cache *new;
+ char *tmp_name;
BUG_ON(!memcg_can_account_kmem(memcg));
- mutex_lock(&mutex);
/*
- * kmem_cache_create_memcg duplicates the given name and
- * cgroup_name for this name requires RCU context.
- * This static temporary buffer is used to prevent from
- * pointless shortliving allocation.
+ * kmem_cache_create_memcg duplicates the given name and cgroup_name()
+ * for this name requires rcu_read_lock().
*/
- if (!tmp_name) {
- tmp_name = kmalloc(PATH_MAX, GFP_KERNEL);
- if (!tmp_name)
- goto out;
- }
+ tmp_name = kmalloc(PATH_MAX, GFP_KERNEL);
+ if (!tmp_name)
+ return NULL;
rcu_read_lock();
snprintf(tmp_name, PATH_MAX, "%s(%d:%s)", s->name,
@@ -3430,8 +3424,7 @@ static struct kmem_cache *memcg_create_k
new->allocflags |= __GFP_KMEMCG;
else
new = s;
-out:
- mutex_unlock(&mutex);
+ kfree(tmp_name);
return new;
}
_
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