Commit 060807f8 authored by Vlastimil Babka's avatar Vlastimil Babka Committed by Linus Torvalds
Browse files

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: default avatarVlastimil Babka <vbabka@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Acked-by: default avatarRoman 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: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 32a6f409

Documentation/vm/slub.rst

+2 −5
Original line number Diff line number Diff line
@@ -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

============

mm/slub.c

+3 −59
Original line number Diff line number Diff line
@@ -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)