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10:33:13PM +0800, Hao Ge wrote: > From: Hao Ge > > If two competing threads enter alloc_slab_obj_exts(), if the process > that allocates the vector wins cmpxchg(), and the other thread mistakenly > assume slab->obj_ext is still empty due to its own allocation failure. Massaging this a little bit: "If two competing threads enter alloc_slab_obj_exts(), and the one that allocates the vector wins the cmpxchg(), the other thread that failed allocation mistakenly assumes that slab->obj_exts is still empty due to its own allocation failure." > This > will then trigger warnings enforced by CONFIG_MEM_ALLOC_PROFILING_DEBUG > checks in the subsequent free path. > > Therefore, let's add an additional check when the process that allocates > the vector loses the cmpxchg() You mean "when the process that failed to allocate the vector loses the cmpxchg()"? > Suggested-by: Harry Yoo > Signed-off-by: Hao Ge > --- > v2: Revise the solution according to Harry's suggestion. > Add Suggested-by: Harry Yoo > --- > > mm/slub.c | 16 +++++++++++----- > 1 file changed, 11 insertions(+), 5 deletions(-) > > diff --git a/mm/slub.c b/mm/slub.c > index d4403341c9df..d7bfec6c0171 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -2052,9 +2052,9 @@ static inline void mark_objexts_empty(struct slabobj_ext *obj_exts) > } > } > > -static inline void mark_failed_objexts_alloc(struct slab *slab) > +static inline bool mark_failed_objexts_alloc(struct slab *slab) > { > - cmpxchg(&slab->obj_exts, 0, OBJEXTS_ALLOC_FAIL); > + return cmpxchg(&slab->obj_exts, 0, OBJEXTS_ALLOC_FAIL) == 0; > } > > static inline void handle_failed_objexts_alloc(unsigned long obj_exts, > @@ -2076,7 +2076,7 @@ static inline void handle_failed_objexts_alloc(unsigned long obj_exts, > #else /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */ > > static inline void mark_objexts_empty(struct slabobj_ext *obj_exts) {} > -static inline void mark_failed_objexts_alloc(struct slab *slab) {} > +static inline bool mark_failed_objexts_alloc(struct slab *slab) { return false; } > static inline void handle_failed_objexts_alloc(unsigned long obj_exts, > struct slabobj_ext *vec, unsigned int objects) {} > > @@ -2124,8 +2124,14 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, > slab_nid(slab)); > } > if (!vec) { > - /* Mark vectors which failed to allocate */ > - mark_failed_objexts_alloc(slab); > + /* > + * Try to mark vectors which failed to allocate nit: ^ missing period (.) here With the comments resolved, Reviewed-by: Harry Yoo > + * If this operation fails, there may be a racing process > + * that has already completed the allocation. > + */ > + if (!mark_failed_objexts_alloc(slab) && > + slab_obj_exts(slab)) > + return 0; > > return -ENOMEM; > } > -- > 2.25.1 -- Cheers, Harry / Hyeonggon