On 9/20/22 10:20, Alexander Atanasov wrote: > In (060807f841ac mm, slub: make remaining slub_debug related attributes > read-only failslab) it was made RO. "read-only) failslab was made RO" ? > I think it became a collateral victim to the other two options > (sanity_checks and trace) for which the reasons are perfectly valid. The commit also mentioned that modifying the flags is not protected in any way, see below. > 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. 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 | 14 +++++++++++++- > 2 files changed, 15 insertions(+), 1 deletion(-) > > 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..7c15d312e0fb 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -5617,7 +5617,19 @@ 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; > + > + s->flags &= ~SLAB_FAILSLAB; > + if (buf[0] == '1') > + s->flags |= SLAB_FAILSLAB; Could we at least use a temporary variable to set up the final value and then do a WRITE_ONCE() to s->flags, so the compiler is not allowed to do some funky stuff? Assuming this is really the only place where we modify s->flags during runtime, so we can't miss other updates due to RMW. > + return length; > +} > +SLAB_ATTR(failslab); > #endif > > static ssize_t shrink_show(struct kmem_cache *s, char *buf) > > base-commit: 80e78fcce86de0288793a0ef0f6acf37656ee4cf
