From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Subject: slub/memcg: cure the brainless abuse of sysfs attributes
memcg_propagate_slab_attrs() abuses the sysfs attribute file functions to
propagate settings from the root kmem_cache to a newly created kmem_cache.
It does that with:
attr->show(root, buf);
attr->store(new, buf, strlen(bug);
Aside of being a lazy and absurd hackery this is broken because it does
not check the return value of the show() function.
Some of the show() functions return 0 w/o touching the buffer. That means
in such a case the store function is called with the stale content of the
previous show(). That causes nonsense like invoking kmem_cache_shrink()
on a newly created kmem_cache. In the worst case it would cause handing
in an uninitialized buffer.
This should be rewritten proper by adding a propagate() callback to those
slub_attributes which must be propagated and avoid that insane conversion
to and from ASCII, but that's too large for a hot fix.
Check at least the return value of the show() function, so calling store()
with stale content is prevented.
Steven said:
: It can cause a deadlock with get_online_cpus() that has been uncovered
: by recent cpu hotplug and lockdep changes that Thomas and Peter have
: been doing.
:
: [ 102.567308] Possible unsafe locking scenario:
: [ 102.567308]
: [ 102.574846] CPU0 CPU1
: [ 102.580148] ---- ----
: [ 102.585421] lock(cpu_hotplug.lock);
: [ 102.589808] lock(slab_mutex);
: [ 102.596166] lock(cpu_hotplug.lock);
: [ 102.603028] lock(slab_mutex);
: [ 102.606846]
: [ 102.606846] *** DEADLOCK ***
Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1705201244540.2255@nanos
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reported-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/slub.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff -puN mm/slub.c~slub-memcg-cure-the-brainless-abuse-of-sysfs-attributes mm/slub.c
--- a/mm/slub.c~slub-memcg-cure-the-brainless-abuse-of-sysfs-attributes
+++ a/mm/slub.c
@@ -5512,6 +5512,7 @@ static void memcg_propagate_slab_attrs(s
char mbuf[64];
char *buf;
struct slab_attribute *attr = to_slab_attr(slab_attrs[i]);
+ ssize_t len;
if (!attr || !attr->store || !attr->show)
continue;
@@ -5536,8 +5537,9 @@ static void memcg_propagate_slab_attrs(s
buf = buffer;
}
- attr->show(root_cache, buf);
- attr->store(s, buf, strlen(buf));
+ len = attr->show(root_cache, buf);
+ if (len > 0)
+ attr->store(s, buf, len);
}
if (buffer)
_