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dkim=none (message not signed) header.d=none;linux-foundation.org; dmarc=none action=none header.from=oracle.com; Received: from CY4PR10MB2038.namprd10.prod.outlook.com (2603:10b6:903:122::20) by CY4PR10MB1959.namprd10.prod.outlook.com (2603:10b6:903:126::15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3868.29; Thu, 25 Feb 2021 07:08:09 +0000 Received: from CY4PR10MB2038.namprd10.prod.outlook.com ([fe80::842f:b854:7899:e759]) by CY4PR10MB2038.namprd10.prod.outlook.com ([fe80::842f:b854:7899:e759%8]) with mapi id 15.20.3868.033; Thu, 25 Feb 2021 07:08:09 +0000 Subject: Re: [patch 014/173] mm, tracing: record slab name for kmem_cache_free() To: Steven Rostedt , Andrew Morton , Joe Perches Cc: cl@linux.com, iamjoonsoo.kim@lge.com, linux-mm@kvack.org, mm-commits@vger.kernel.org, paulmck@linux.vnet.ibm.com, penberg@kernel.org, rientjes@google.com, torvalds@linux-foundation.org References: <20210224115824.1e289a6895087f10c41dd8d6@linux-foundation.org> <20210224200055.U7Xz47kX5%akpm@linux-foundation.org> <20210224203708.4489755a@oasis.local.home> <20210224210740.73273c7a@oasis.local.home> From: Jacob Wen Message-ID: <5a0b6fb4-6efd-e391-45fa-cd188f181d5d@oracle.com> Date: Thu, 25 Feb 2021 15:07:50 +0800 User-Agent: Mozilla/5.0 (X11; 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Well, >> the s->name that __entry->name points to, can be long gone by then! >> >> Instead, using __string() tells the TRACE_EVENT() macro that this is a >> dynamic string. The __assign_str() records the string into the ring >> buffer. The __get_str() retrieves the string from the ring buffer as >> part of the event, so it stays around as long as the event being read >> by the trace file is around. >> >> Please do not apply this patch as is, it is very buggy! > I wonder if we can add something to checkpatch that can check if > TP_printk() has a call to "%s" where it references a __entry->xxx and > not a __get_str(), and will warn about it. That's helpful for me who don't know "%s" of TP_printk is special. > > There a a few cases where its OK. Like RCU uses a TPS() macro around > strings it passes into the tracepoint, which is used for strings that > never are freed, and maps the string pointer to the string for user > space. But RCU is the only user of that I believe. > > -- Steve