Commit 7c82b3b3 authored by Alexander Atanasov's avatar Alexander Atanasov Committed by Vlastimil Babka
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mm: Make failslab writable again 

In (060807f8 mm, slub: make remaining slub_debug related attributes
read-only) failslab was made read-only.
I think it became a collateral victim to the two other options for which
the reasons are perfectly valid.
Here is why:
 - sanity_checks and trace are slab internal debug options,
   failslab is used for fault injection.
 - for fault injections, which by presumption are random, it
   does not matter if it is not set atomically. And you need to
   set atleast one more option to trigger fault injection.
 - in a testing scenario you may need to change it at runtime
   example: module loading - you test all allocations limited
   by the space option. Then you move to test only your module's
   own slabs.
 - when set by command line flags it effectively disables all
   cache merges.

Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: 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: default avatarAlexander Atanasov <alexander.atanasov@virtuozzo.com>
Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
parent 1a5ad30b

Documentation/mm/slub.rst

+2 −0
Original line number Diff line number Diff line
@@ -116,6 +116,8 @@ options from the ``slub_debug`` parameter translate to the following files:: 
	T	trace

	A	failslab



failslab file is writable, so writing 1 or 0 will enable or disable

the option at runtime. Write returns -EINVAL if cache is an alias.

Careful with tracing: It may spew out lots of information and never stop if

used on the wrong slab.

mm/slub.c

+15 −1
Original line number Diff line number Diff line
@@ -5586,7 +5586,21 @@ static ssize_t failslab_show(struct kmem_cache *s, char *buf) 
{

	return sysfs_emit(buf, "%d\n", !!(s->flags & SLAB_FAILSLAB));

}

SLAB_ATTR_RO(failslab);



static ssize_t failslab_store(struct kmem_cache *s, const char *buf,

				size_t length)

{

	if (s->refcount > 1)

		return -EINVAL;



	if (buf[0] == '1')

		WRITE_ONCE(s->flags, s->flags | SLAB_FAILSLAB);

	else

		WRITE_ONCE(s->flags, s->flags & ~SLAB_FAILSLAB);



	return length;

}

SLAB_ATTR(failslab);

#endif



static ssize_t shrink_show(struct kmem_cache *s, char *buf)