On 2021/11/2 19:43, Yunfeng Ye wrote: > After the memory is freed, it can be immediately allocated by other > CPUs, before the "free" trace report has been emitted. This causes > inaccurate traces. > > For example, if the following sequence of events occurs: > > CPU 0 CPU 1 > > (1) alloc xxxxxx > (2) free xxxxxx > (3) alloc xxxxxx > (4) free xxxxxx > > Then they will be inaccurately reported via tracing, so that they appear > to have happened in this order: > > CPU 0 CPU 1 > > (1) alloc xxxxxx > (2) alloc xxxxxx > (3) free xxxxxx > (4) free xxxxxx > > This makes it look like CPU 1 somehow managed to allocate mmemory that > CPU 0 still had allocated for itself. > > In order to avoid this, emit the "free xxxxxx" tracing report just > before the actual call to free the memory, instead of just after it. > > Signed-off-by: Yunfeng Ye <yeyunfeng@xxxxxxxxxx> > Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx> > --- > v1 -> v2: > - Modify the description > - Add "Reviewed-by" > > mm/slub.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/slub.c b/mm/slub.c > index 432145d7b4ec..427e62034c3f 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -3526,8 +3526,8 @@ void kmem_cache_free(struct kmem_cache *s, void *x) > s = cache_from_obj(s, x); > if (!s) > return; > - slab_free(s, virt_to_head_page(x), x, NULL, 1, _RET_IP_); > trace_kmem_cache_free(_RET_IP_, x, s->name); > + slab_free(s, virt_to_head_page(x), x, NULL, 1, _RET_IP_); > } It seems that kmem_cache_free() in mm/slab.c has the same problem. We can fix it. Thanks. > EXPORT_SYMBOL(kmem_cache_free); >
