mm, slub: make remaining slub_debug related attributes read-only

SLUB_DEBUG creates several files under /sys/kernel/slab/<cache>/ that can
be read to check if the respective debugging options are enabled for given
cache.  Some options, namely sanity_checks, trace, and failslab can be
also enabled and disabled at runtime by writing into the files.

The runtime toggling is racy.  Some options disable __CMPXCHG_DOUBLE when
enabled, which means that in case of concurrent allocations, some can
still use __CMPXCHG_DOUBLE and some not, leading to potential corruption.
The s->flags field is also not updated or checked atomically.  The
simplest solution is to remove the runtime toggling.  The extended
slub_debug boot parameter syntax introduced by earlier patch should allow
to fine-tune the debugging configuration during boot with same
granularity.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Roman Gushchin <guro@fb.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Jann Horn <jannh@google.com>
Cc: Vijayanand Jitta <vjitta@codeaurora.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Pekka Enberg <penberg@kernel.org>
Link: http://lkml.kernel.org/r/20200610163135.17364-5-vbabka@suse.cz
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/Documentation/vm/slub.rst b/Documentation/vm/slub.rst
index 36241dfba0243471c585986ddb288019398e63b5..289d231cee97266f01dcc8c2271bd66875361c5a 100644 (file)
--- a/Documentation/vm/slub.rst
+++ b/Documentation/vm/slub.rst
@@ -116,11 +116,8 @@ options from the ``slub_debug`` parameter translate to the following files::
        T       trace
        A       failslab
 
-The sanity_checks, trace and failslab files are writable, so writing 1 or 0
-will enable or disable the option at runtime. The writes to trace and failslab
-may return -EINVAL if the cache is subject to slab merging. Careful with
-tracing: It may spew out lots of information and never stop if used on the
-wrong slab.
+Careful with tracing: It may spew out lots of information and never stop if
+used on the wrong slab.
 
 Slab merging
 ============

diff --git a/mm/slub.c b/mm/slub.c
index f03b1073bdcfcf873068a283f8cc49fcc9911ce1..5848b7c3575aa73d86716e718c32186ce65f62b8 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5040,20 +5040,6 @@ static ssize_t show_slab_objects(struct kmem_cache *s,
        return x + sprintf(buf + x, "\n");
 }
 
-#ifdef CONFIG_SLUB_DEBUG
-static int any_slab_objects(struct kmem_cache *s)
-{
-       int node;
-       struct kmem_cache_node *n;
-
-       for_each_kmem_cache_node(s, node, n)
-               if (atomic_long_read(&n->total_objects))
-                       return 1;
-
-       return 0;
-}
-#endif
-
 #define to_slab_attr(n) container_of(n, struct slab_attribute, attr)
 #define to_slab(n) container_of(n, struct kmem_cache, kobj)
 
@@ -5275,43 +5261,13 @@ static ssize_t sanity_checks_show(struct kmem_cache *s, char *buf)
 {
        return sprintf(buf, "%d\n", !!(s->flags & SLAB_CONSISTENCY_CHECKS));
 }
-
-static ssize_t sanity_checks_store(struct kmem_cache *s,
-                               const char *buf, size_t length)
-{
-       s->flags &= ~SLAB_CONSISTENCY_CHECKS;
-       if (buf[0] == '1') {
-               s->flags &= ~__CMPXCHG_DOUBLE;
-               s->flags |= SLAB_CONSISTENCY_CHECKS;
-       }
-       return length;
-}
-SLAB_ATTR(sanity_checks);
+SLAB_ATTR_RO(sanity_checks);
 
 static ssize_t trace_show(struct kmem_cache *s, char *buf)
 {
        return sprintf(buf, "%d\n", !!(s->flags & SLAB_TRACE));
 }
-
-static ssize_t trace_store(struct kmem_cache *s, const char *buf,
-                                                       size_t length)
-{
-       /*
-        * Tracing a merged cache is going to give confusing results
-        * as well as cause other issues like converting a mergeable
-        * cache into an umergeable one.
-        */
-       if (s->refcount > 1)
-               return -EINVAL;
-
-       s->flags &= ~SLAB_TRACE;
-       if (buf[0] == '1') {
-               s->flags &= ~__CMPXCHG_DOUBLE;
-               s->flags |= SLAB_TRACE;
-       }
-       return length;
-}
-SLAB_ATTR(trace);
+SLAB_ATTR_RO(trace);
 
 static ssize_t red_zone_show(struct kmem_cache *s, char *buf)
 {
@@ -5375,19 +5331,7 @@ static ssize_t failslab_show(struct kmem_cache *s, char *buf)
 {
        return sprintf(buf, "%d\n", !!(s->flags & SLAB_FAILSLAB));
 }
-
-static ssize_t failslab_store(struct kmem_cache *s, const char *buf,
-                                                       size_t length)
-{
-       if (s->refcount > 1)
-               return -EINVAL;
-
-       s->flags &= ~SLAB_FAILSLAB;
-       if (buf[0] == '1')
-               s->flags |= SLAB_FAILSLAB;
-       return length;
-}
-SLAB_ATTR(failslab);
+SLAB_ATTR_RO(failslab);
 #endif
 
 static ssize_t shrink_show(struct kmem_cache *s, char *buf)