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Mon, 28 Jul 2025 15:03:15 -0400 X-MC-Unique: x4zQ7z2HNrONl-LZxjCPUQ-1 X-Mimecast-MFC-AGG-ID: x4zQ7z2HNrONl-LZxjCPUQ_1753729394 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 7A292195609E; Mon, 28 Jul 2025 19:03:13 +0000 (UTC) Received: from llong-thinkpadp16vgen1.westford.csb (unknown [10.22.81.41]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 14EBF1955F16; Mon, 28 Jul 2025 19:03:11 +0000 (UTC) From: Waiman Long To: Catalin Marinas , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Waiman Long Subject: [PATCH] mm/kmemleak: Avoid soft lockup in __kmemleak_do_cleanup() Date: Mon, 28 Jul 2025 15:02:48 -0400 Message-ID: <20250728190248.605750-1-longman@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 652831C0012 X-Stat-Signature: rjzib9cfg8ayq7gxmnagtsuawa4gyb61 X-HE-Tag: 1753729400-671148 X-HE-Meta: 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 zYvWqMcb 0cK2L4wr0mAVKd68P+LMNemVsgS/Ny7bwSd+R4zQgNBOojUdOqelc7HTuZbwqv57IYuwwIkzkfwviiMG4TagB8+4qcOR2fdM8duVHWJFGpGhLGVi+8NFzRN0ZiiMOVyxi7RGq9FBHzx3CU72Q/AG8KfdmJ2mxq+lHvAJTRFqJbU5vmHMejEMRma+DQ2xvJ79TRKh9iJa2fjvWdz7WsOcrXFzIFWQRWpcUJOtEhskw97tgjVSpAm3pZIBMQHn7yP8sjd1gvrLV5Q/klvztPZx4P/XZPtIxkUBOGT4WYhX+eo35dy0m2+AmPTl1kmWQYE/T7WF89nuS3JNi1YVuwbADgrsOODB8MztZu0lqWIANtK70Ky5/zI9tg7WtsA== 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: A soft lockup warning was observed on a relative small system x86-64 system with 16 GB of memory when running a debug kernel with kmemleak enabled. watchdog: BUG: soft lockup - CPU#8 stuck for 33s! [kworker/8:1:134] The test system was running a workload with hot unplug happening in parallel. Then kemleak decided to disable itself due to its inability to allocate more kmemleak objects. The debug kernel has its CONFIG_DEBUG_KMEMLEAK_MEM_POOL_SIZE set to 40,000. The soft lockup happened in kmemleak_do_cleanup() when the existing kmemleak objects were being removed and deleted one-by-one in a loop via a workqueue. In this particular case, there are at least 40,000 objects that need to be processed and given the slowness of a debug kernel and the fact that a raw_spinlock has to be acquired and released in __delete_object(), it could take a while to properly handle all these objects. As kmemleak has been disabled in this case, the object removal and deletion process can be further optimized as locking isn't really needed. However, it is probably not worth the effort to optimize for such an edge case that should rarely happen. So the simple solution is to call cond_resched() at periodic interval in the iteration loop to avoid soft lockup. Signed-off-by: Waiman Long --- mm/kmemleak.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/mm/kmemleak.c b/mm/kmemleak.c index 8d588e685311..620abd95e680 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -2181,6 +2181,7 @@ static const struct file_operations kmemleak_fops = { static void __kmemleak_do_cleanup(void) { struct kmemleak_object *object, *tmp; + unsigned int cnt = 0; /* * Kmemleak has already been disabled, no need for RCU list traversal @@ -2189,6 +2190,10 @@ static void __kmemleak_do_cleanup(void) list_for_each_entry_safe(object, tmp, &object_list, object_list) { __remove_object(object); __delete_object(object); + + /* Call cond_resched() once per 64 iterations to avoid soft lockup */ + if (!(++cnt & 0x3f)) + cond_resched(); } } -- 2.50.0