In (060807f841ac 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@xxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Roman Gushchin <guro@xxxxxx> Cc: Christoph Lameter <cl@xxxxxxxxx> Cc: Jann Horn <jannh@xxxxxxxxxx> Cc: Vijayanand Jitta <vjitta@xxxxxxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: Pekka Enberg <penberg@xxxxxxxxxx> Link: http://lkml.kernel.org/r/20200610163135.17364-5-vbabka@xxxxxxx Signed-off-by: Alexander Atanasov <alexander.atanasov@xxxxxxxxxxxxx> --- Documentation/mm/slub.rst | 2 ++ mm/slub.c | 16 +++++++++++++++- 2 files changed, 17 insertions(+), 1 deletion(-) V1->V2: Fixed commit message. Flags are set using WRITE_ONCE. diff --git a/Documentation/mm/slub.rst b/Documentation/mm/slub.rst index 43063ade737a..86837073a39e 100644 --- a/Documentation/mm/slub.rst +++ b/Documentation/mm/slub.rst @@ -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. diff --git a/mm/slub.c b/mm/slub.c index 862dbd9af4f5..57cf18936526 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -5617,7 +5617,21 @@ 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) base-commit: 80e78fcce86de0288793a0ef0f6acf37656ee4cf -- 2.31.1
