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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>
This commit is contained in:
Vlastimil Babka 2020-08-06 23:18:45 -07:00 committed by Linus Torvalds
parent 32a6f409b6
commit 060807f841
2 changed files with 5 additions and 64 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
Documentation/vm/slub.rst
View File

@ -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
============

62
mm/slub.c
View File

@ -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)