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([2601:188:c180:4250:ecbe:130d:668d:951d]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7e87e1c14aesm860958585a.69.2025.08.19.20.27.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 19 Aug 2025 20:27:24 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <113a8332-b35c-4d00-b8b1-21c07d133f1f@redhat.com> Date: Tue, 19 Aug 2025 23:27:23 -0400 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] mm: Fix possible deadlock in kmemleak To: Gu Bowen , Catalin Marinas , Andrew Morton , Greg Kroah-Hartman Cc: stable@vger.kernel.org, linux-mm@kvack.org, Waiman Long , Breno Leitao , John Ogness , Lu Jialin References: <20250818090945.1003644-1-gubowen5@huawei.com> In-Reply-To: <20250818090945.1003644-1-gubowen5@huawei.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: NDwG1QZt4tq8jTBUpJcVMn0KcPeZMX-bmd6d1PAF9T4_1755660446 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: 8s67aqbwyhfhm6ddkq5ot9aoowe5hjmh X-Rspam-User: X-Rspamd-Queue-Id: A509C40005 X-Rspamd-Server: rspam05 X-HE-Tag: 1755660448-940448 X-HE-Meta: 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 fIQkFMvZ 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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 8/18/25 5:09 AM, Gu Bowen wrote: > Our syztester report the lockdep WARNING [1], which was identified in > stable kernel version 5.10. However, this deadlock path no longer exists > due to the refactoring of console_lock in v6.2-rc1 [2]. Coincidentally, > there are two types of deadlocks that we have found here. One is the ABBA > deadlock, as mentioned above [1], and the other is the AA deadlock was > reported by Breno [3]. The latter's deadlock issue persists. > > To solve this problem, switch to printk_safe mode before printing warning > message, this will redirect all printk()-s to a special per-CPU buffer, > which will be flushed later from a safe context (irq work), and this > deadlock problem can be avoided. The proper API to use should be > printk_deferred_enter()/printk_deferred_exit() [4]. > > [1] > https://lore.kernel.org/all/20250730094914.566582-1-gubowen5@huawei.com/ > [2] > https://lore.kernel.org/all/20221116162152.193147-1-john.ogness@linutronix.de/ > [3] > https://lore.kernel.org/all/20250731-kmemleak_lock-v1-1-728fd470198f@debian.org/#t > [4] > https://lore.kernel.org/all/5ca375cd-4a20-4807-b897-68b289626550@redhat.com/ > ==================== > > Signed-off-by: Gu Bowen > --- > mm/kmemleak.c | 18 ++++++++++++++++++ > 1 file changed, 18 insertions(+) > > diff --git a/mm/kmemleak.c b/mm/kmemleak.c > index 84265983f239..26113b89d09b 100644 > --- a/mm/kmemleak.c > +++ b/mm/kmemleak.c > @@ -437,9 +437,15 @@ static struct kmemleak_object *__lookup_object(unsigned long ptr, int alias, > else if (untagged_objp == untagged_ptr || alias) > return object; > else { > + /* > + * Printk deferring due to the kmemleak_lock held. > + * This is done to avoid deadlock. > + */ > + printk_deferred_enter(); > kmemleak_warn("Found object by alias at 0x%08lx\n", > ptr); > dump_object_info(object); > + printk_deferred_exit(); > break; > } > } > @@ -736,6 +742,11 @@ static int __link_object(struct kmemleak_object *object, unsigned long ptr, > else if (untagged_objp + parent->size <= untagged_ptr) > link = &parent->rb_node.rb_right; > else { > + /* > + * Printk deferring due to the kmemleak_lock held. > + * This is done to avoid deadlock. > + */ > + printk_deferred_enter(); > kmemleak_stop("Cannot insert 0x%lx into the object search tree (overlaps existing)\n", > ptr); > /* > @@ -743,6 +754,7 @@ static int __link_object(struct kmemleak_object *object, unsigned long ptr, > * be freed while the kmemleak_lock is held. > */ > dump_object_info(parent); > + printk_deferred_exit(); > return -EEXIST; > } > } > @@ -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. Anyway, it is just a nit. Acked-by: Waiman Long