Messages in this thread | | | Date | Wed, 23 Nov 2022 14:17:24 +0100 | Subject | Re: [PATCH] mm/tracing: Add check for kmem_cache | From | Vlastimil Babka <> |
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On 11/23/22 12:10, Jiasheng Jiang wrote: > In __kmem_cache_alloc_lru() of mm/slab.c, cachep may be NULL when error > occurs in slab_alloc().
Are you sure? AFAICS internally in slab_alloc_node(), slab_pre_alloc_hook() can return NULL which is assigned to cachep local variable, but only NULL propagated back to __kmem_cache_alloc_lru() is the object, not cachep. So trace_kmem_cache_alloc() should only see NULL s, if it was already NULL when passed to kmem_cache_alloc(), at which point the NULL is dereferenced and crashing (as expected) earlier than reaching the tracepoint.
> However, trace_kmem_cache_alloc() will still use it as the parameter, > which may cause NULL poineter dereference. > Therefore, it should be better to add the check and handle the error > in the trace_kmem_cache_alloc(). > > Fixes: 36555751c675 ("kmemtrace: SLAB hooks.") > Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn> > --- > include/trace/events/kmem.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h > index 243073cfc29d..d99507d32ef5 100644 > --- a/include/trace/events/kmem.h > +++ b/include/trace/events/kmem.h > @@ -32,8 +32,8 @@ TRACE_EVENT(kmem_cache_alloc, > TP_fast_assign( > __entry->call_site = call_site; > __entry->ptr = ptr; > - __entry->bytes_req = s->object_size; > - __entry->bytes_alloc = s->size; > + __entry->bytes_req = s ? s->object_size : 0; > + __entry->bytes_alloc = s ? s->size : 0; > __entry->gfp_flags = (__force unsigned long)gfp_flags; > __entry->node = node; > __entry->accounted = IS_ENABLED(CONFIG_MEMCG_KMEM) ?
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