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From: Hao Ge To: Harry Yoo Cc: Vlastimil Babka , Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , Suren Baghdasaryan , Shakeel Butt , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hao Ge References: <20251023012117.890883-1-hao.ge@linux.dev> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: i38x9iyu1gb97iim7fqmwscybae1p9g3 X-Rspamd-Queue-Id: 46AC080002 X-Rspamd-Server: rspam06 X-Rspam-User: X-HE-Tag: 1761209267-291936 X-HE-Meta: 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 qHUbGt/r zOJVIThZClKHknXTtOzpKml8NkGca2ztaHyKVwLZ7Kr6NWvS/jHuT/BCC2FKzomK989RCQKz6I1ojrDNV+vK2ZcYLrH5ms2kO91S5b4FWO+LW4rhPPmIev35PWAoX6zTP4Acz2xHtFd4XVBSP+bRjVFNlPAf2dOuL0yv0WkfA79XUBClm8JtkMTpHdTKcMnrrGi9MH4OmlS1fgScFCwtMPETFUJHcAgZGn3HDko4DhCd7kaG7LlQQ0i8sRw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Harry On 2025/10/23 16:23, Hao Ge wrote: > Hi Harry > > > On 2025/10/23 15:50, Harry Yoo wrote: >> On Thu, Oct 23, 2025 at 11:11:56AM +0800, Hao Ge wrote: >>> Hi Harry >>> >>> >>> On 2025/10/23 10:24, Harry Yoo wrote: >>>> On Thu, Oct 23, 2025 at 09:21:17AM +0800, Hao Ge wrote: >>>>> From: Hao Ge >>>>> >>>>> If two competing threads enter alloc_slab_obj_exts(), and the >>>>> thread that failed to allocate the object extension vector exits >>>>> after the one that succeeded, it will mistakenly assume slab->obj_ext >>>>> 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 alloc_slab_obj_exts >>>>> fails. >>>>> >>>>> Signed-off-by: Hao Ge >>>>> --- >>>>>    mm/slub.c | 9 ++++++--- >>>>>    1 file changed, 6 insertions(+), 3 deletions(-) >>>>> >>>>> diff --git a/mm/slub.c b/mm/slub.c >>>>> index d4403341c9df..42276f0cc920 100644 >>>>> --- a/mm/slub.c >>>>> +++ b/mm/slub.c >>>>> @@ -2227,9 +2227,12 @@ prepare_slab_obj_exts_hook(struct >>>>> kmem_cache *s, gfp_t flags, void *p) >>>>>        slab = virt_to_slab(p); >>>>>        if (!slab_obj_exts(slab) && >>>>>            alloc_slab_obj_exts(slab, s, flags, false)) { >>>>> -        pr_warn_once("%s, %s: Failed to create slab extension >>>>> vector!\n", >>>>> -                 __func__, s->name); >>>>> -        return NULL; >>>>> +        /* Recheck if a racing thread has successfully allocated >>>>> slab->obj_exts. */ >>>>> +        if (!slab_obj_exts(slab)) { >>>>> +            pr_warn_once("%s, %s: Failed to create slab extension >>>>> vector!\n", >>>>> +                     __func__, s->name); >>>>> +            return NULL; >>>>> +        } >>>>>        } >>>> Maybe this patch is a bit paranoid... since if >>>> mark_failed_objexts_alloc() >>>> win cmpxchg() and then someone else allocates the object extension >>>> vector, >>>> the warning will still be printed anyway. >> Oh, just to be clear I was talking about the other warning: >> pr_warn_once("%s, %s: Failed to create slab extension vector!", >> __func__, s->name); >> >>> The process that successfully allocates slab_exts will call >>> handle_failed_objexts_alloc, setting ref->ct = CODETAG_EMPTY >>> to prevent the warning from being triggered. >> But yeah I see what you mean. >> >> As you mentioned, if the process that failed to allocate the vector wins >> cmpxchg(), later process that successfully allocate the vector would >> call set_codetag_empty(), so no warning. >> >> But if the process that allocates the vector wins cmpxchg(), >> then it won't call set_codetag_empty(), so the process >> that was trying to set OBJEXTS_ALLOC_FAIL now needs to set the tag. > > Yes, the case I'm encountering is exactly this one. > >> >>>> But anyway, I think there is a better way to do this: >> What do you think about the diff I suggested below, though? > > Sorry for the delayed response earlier; I was trying to deduce all > possible scenarios. > > It makes sense to me, and I will submit the V2 version based on this > suggestion. > > Thank you for your help. > >> >>>> diff --git a/mm/slub.c b/mm/slub.c >>>> index dd4c85ea1038..d08d7580349d 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 true; } Maybe it returns false here. When CONFIG_MEM_ALLOC_PROFILING_DEBUG is not enabled, The following condition will never be executed: if (!mark_failed_objexts_alloc(slab) && slab_obj_exts(slab)) if another process that allocates the vector, we will lose one count. >>>>    static inline void handle_failed_objexts_alloc(unsigned long >>>> obj_exts, >>>>                struct slabobj_ext *vec, unsigned int objects) {} >>>> @@ -2125,7 +2125,9 @@ int alloc_slab_obj_exts(struct slab *slab, >>>> struct kmem_cache *s, >>>>        } >>>>        if (!vec) { >>>>            /* Mark vectors which failed to allocate */ >>>> -        mark_failed_objexts_alloc(slab); >>>> +        if (!mark_failed_objexts_alloc(slab) && >>>> +            slab_obj_exts(slab)) >>>> +            return 0; >>>>            return -ENOMEM; >>>>        } >>>>