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([2601:188:c180:4250:ecbe:130d:668d:951d]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7e87e027290sm969604785a.5.2025.08.20.08.01.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 20 Aug 2025 08:01:03 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: Date: Wed, 20 Aug 2025 11:01:00 -0400 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] mm: Fix possible deadlock in kmemleak To: Catalin Marinas , Waiman Long Cc: Gu Bowen , Andrew Morton , Greg Kroah-Hartman , stable@vger.kernel.org, linux-mm@kvack.org, Breno Leitao , John Ogness , Lu Jialin References: <20250818090945.1003644-1-gubowen5@huawei.com> <113a8332-b35c-4d00-b8b1-21c07d133f1f@redhat.com> In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: LqUS9qwoNDZfEo5wlylFOzc-pvzskm4plv8igXYV8ic_1755702080 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 2FE6816002C X-Stat-Signature: 4aiofapow6q6k71zi4x74nzxjsgpxss7 X-Rspam-User: X-HE-Tag: 1755702082-333603 X-HE-Meta: U2FsdGVkX18LVQA0cVtDtQmiNYsdo15MfoWA80ziZdJW6Vmk6d/LHvItcPFpze5KrSvBj6GaI5Ho0aCk0opJ5k1UopIHw4bhyjso7wwm+LpDrVzBnryHTrlU/3/E19bNfUizQK0tEAMOF17Zs45lsvNz8JAgw3OzZZs8Kweei/4Xta9FEDouLoCeGjbLMx/yFSue4WCbB6yTDXx/m2Id6pyt2KNBncLpRlLv4AswIs3RfEGHAuBpvhK3faFPwuraOtc5HForD849odFOXA/wheC9G7OnZ5HNldegURABq7ygZyE4js+KRdzyb2bqyjbAhsM1esQdcGhD1V2mWj8V3kcPMQIU0zdnP8861g0cYieOMPPFOY+N8pobbOh7DkcIbuw5WWT1ylhbbkqREGsJYYfMg5VGy3TyG2uT1rmgEo1l9VLUWLEKo54CObbCxDiA1i568Xz/bxJc6rawWev3yYttsfgSA7eDVaqrOG1d+Y+Nw+Sc0c+L4CrA2q6Xy2WKxHJ9TdS0c2pbKlYZzQPEJ3Y3+2nvkZayar8mZ42SRxZvY8xJbF/x4eYEsqWXnC1jpqo9JDYFMabnj2MpfFwydby1B2e6/W36PUKwwdOVBv94t/0JdTIepe1dOetwbqGnexN/DGlf6E38Za6ji5mb2W54G/McsCAZ8rqjxJ9QmIfN4Bb1PWrM5V3Sy0A5nVD6YYhKWux01CG+rUXh/bYGo7pD0ewJQwhjXew9m3+AsXp1bh1VZL9hghrJBIMViy4x/ViMNoeDVbub1uK+Ak1Fch33dklr9ioa7WmrQ9wvADwzzTsUeSPJ/7zbiEpIWazvzBFxKpTQXK7gnqJs/fUmWfVb8ciNpNume4xLm/9meSrrrJF7rH3OxTDgYbaLkkHR55/Fd5wE2EirGDSERSRKfnGu2sNkGO4KtswoB6kDCnWt2Re48keNYxMwdbsNZG2XnJZgio6Nn5GIEcE94p8 Z3jsY5AH 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 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: On 8/20/25 7:02 AM, Catalin Marinas wrote: > On Tue, Aug 19, 2025 at 11:27:23PM -0400, Waiman Long wrote: >> On 8/18/25 5:09 AM, Gu Bowen wrote: >>> @@ -858,8 +870,14 @@ static void delete_object_part(unsigned long ptr, size_t size, >>> object = __find_and_remove_object(ptr, 1, objflags); >>> if (!object) { >>> #ifdef DEBUG >>> + /* >>> + * Printk deferring due to the kmemleak_lock held. >>> + * This is done to avoid deadlock. >>> + */ >>> + printk_deferred_enter(); >>> kmemleak_warn("Partially freeing unknown object at 0x%08lx (size %zu)\n", >>> ptr, size); >>> + printk_deferred_exit(); >>> #endif >> This particular warning message can be moved after unlock by adding a >> warning flag. Locking is done outside of the other two helper functions >> above, so it is easier to use printk_deferred_enter/exit() for those. > I thought about this as well but the above is under an #ifdef DEBUG so > we end up adding more lines on the unlock path (not sure which one looks > better; I'd say the above, marginally). > > Another option would be to remove the #ifdef and try to identify the > call sites that trigger the warning. Last time I checked (many years > ago) they were fairly benign and decided to hide them before an #ifdef. A bit more code change required the printing is moved. diff --git a/mm/kmemleak.c b/mm/kmemleak.c index 84265983f239..eb4e0af5edba 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -856,13 +856,8 @@ static void delete_object_part(unsigned long ptr, size_t size,         raw_spin_lock_irqsave(&kmemleak_lock, flags);         object = __find_and_remove_object(ptr, 1, objflags); -       if (!object) { -#ifdef DEBUG -               kmemleak_warn("Partially freeing unknown object at 0x%08lx (size %zu)\n", -                             ptr, size); -#endif +       if (!object)                 goto unlock; -       }         /*          * Create one or two objects that may result from the memory block @@ -882,8 +877,14 @@ static void delete_object_part(unsigned long ptr, size_t size,  unlock:         raw_spin_unlock_irqrestore(&kmemleak_lock, flags); -       if (object) +       if (object) {                 __delete_object(object); +       } else { +#ifdef DEBUG +               kmemleak_warn("Partially freeing unknown object at 0x%08lx (size %zu)\n", +                             ptr, size); +#endif +       } Anyway, I am not against using printk_deferred_enter/exit here. It is just that they should be used as a last resort if there is no easy way to work around it. Cheers, Longman