From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 35662 invoked by alias); 23 Jan 2017 22:43:42 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 35234 invoked by uid 89); 23 Jan 2017 22:43:36 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-HELO: sessmg23.ericsson.net Received: from sessmg23.ericsson.net (HELO sessmg23.ericsson.net) (193.180.251.45) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Mon, 23 Jan 2017 22:43:35 +0000 Received: from ESESSHC023.ericsson.se (Unknown_Domain [153.88.253.124]) by (Symantec Mail Security) with SMTP id 09.95.32317.41786885; Mon, 23 Jan 2017 23:43:32 +0100 (CET) Received: from EUR01-VE1-obe.outbound.protection.outlook.com (153.88.183.145) by oa.msg.ericsson.com (153.88.183.87) with Microsoft SMTP Server (TLS) id 14.3.319.2; Mon, 23 Jan 2017 23:42:57 +0100 Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=simon.marchi@ericsson.com; Received: from elxcz23q12-y4.ca.am.ericsson.se (192.75.88.130) by DBXPR07MB399.eurprd07.prod.outlook.com (10.141.14.149) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384_P384) id 15.1.874.6; Mon, 23 Jan 2017 22:40:41 +0000 From: Simon Marchi To: CC: Simon Marchi Subject: [PATCH 5/5] Add missing incref when creating Inferior Python object Date: Mon, 23 Jan 2017 22:43:00 -0000 Message-ID: <20170123224004.8893-6-simon.marchi@ericsson.com> In-Reply-To: <20170123224004.8893-1-simon.marchi@ericsson.com> References: <20170123224004.8893-1-simon.marchi@ericsson.com> MIME-Version: 1.0 Content-Type: text/plain X-ClientProxiedBy: CY4PR13CA0008.namprd13.prod.outlook.com (10.168.161.146) To DBXPR07MB399.eurprd07.prod.outlook.com (10.141.14.149) X-MS-Office365-Filtering-Correlation-Id: 4363e283-002f-4bd9-2a6b-08d443e0dcff X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:(22001);SRVR:DBXPR07MB399; X-Microsoft-Exchange-Diagnostics: 1;DBXPR07MB399;3:9TXBSkHqQRyoK8A0yuM6tGh6whcLFT+kMQ0c2UswEKxU7ODGbv5Ts0BMuS7Echnnmzs3qlwmK97fDtzLP6cn8HT50jUSJ8/XRoNFK2As7DNbPR1jGb5yci6T2b+y/ogafepLgIKZYtaHuMqr2Q+kvTYUo+mTGwKSY56Sl8AoxQJE4/G7B2etkqGJ9yKgDmnsA8g4D/Ax4Lcf+QYx+pLagKCa6JborniX/Zy9PHhuDd3J1urStN0Pc2D36gpq/+vQsCTF2LNdnh/7Ft1p6TSdGA==;25:p51OktVEXr8taOlK2Umdl4xhq5yDcOD8uys9irj2PEPKUy3ghAhL5kKGJyJhe8uXlAwwa7i9C691cB0Y2MjC6qzzjEciGQXDsBPGC04bfuGOhLip2VHf4X4SQMHIAGRjLrEslp4CD59Cps2EsYY3zUtxLql39reAvjFnyudXKX8rozU/qhoubTawg9aXCxXjyIM85coZ610B6z1XZ4iF0VyViKYj6rn47ftVVQqM7cjASXvZ0dVXMRKvMRL5Wiic+BKLR4kVOpkIQXBRoyRlHIKYvx1QAhLz8QFTd54llRdkW9huMAckyeCYuwwG8H7sdchWyPLD9Q7ZVlpnudSNhshbvPO/95jh7+utvzxMJfDh3hYa4T65lHPecgjNYw6w/6E1MER2oeCU+RbWhqRAddVtJVS0k1+2idUUBETvbicwTWRrZr466+lzAtrUB4CMjuGbdoYrcjZQnmPMDDsjxw== X-Microsoft-Exchange-Diagnostics: 1;DBXPR07MB399;31:gifnb64ZmPNbJfWoc/CthALxcrsnSvVIdt4k5dB4RPYwg8o72RxgOAswZ0g1JNjKdDq3xcgouS8lFR669XoFQmBO80qkSShm1wtIpl0/bJCYmygwx15Nq2ZgOyeCxf2BQe50p0h7+qZm88dXyrNLl7RbVOIFSVPEIlB7yeCVx+aAJ4M6z8Rc2Tl2gXamSCPpn/2xQSUdc30uV7rR9mg1Z2VJ6mVSoFdEiCg13W1yt1/WO3RbQl5T0KvDGk8j75NF;20: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 X-Microsoft-Antispam-PRVS: X-Exchange-Antispam-Report-Test: UriScan:; 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I don't see it failing with my system's default Python, but it might be related to the different memory allocation scheme used when doing a build with pydebug. The issue is that we are missing a Py_INCREF in inferior_to_inferior_object. The PyObject_New function initializes the object with a refcount of 1. If we assume that this refcount corresponds to the reference we are keeping in the inferior data, then we are missing an incref for the reference we are returning. We can also see it the other way. If the refcount added by PyObject_New is for the reference we are returning, then we are missing one for the inferior data. The counterpart for this incref is in py_free_inferior. Here's how I can get it to crash: $ ./gdb -nx -ex "set debug python 1" (gdb) add-inferior Added inferior 2 (gdb) python infs = gdb.inferiors() Creating Python Inferior object inf = 1 Creating Python Inferior object inf = 2 (gdb) remove-inferiors 2 py_free_inferior inf = 2 infpy_dealloc inf = (gdb) python infs = None Fatal Python error: Objects/tupleobject.c:243 object at 0x7f9cf1a568d8 has negative ref count -1 Current thread 0x00007f9cf1b68780 (most recent call first): File "", line 1 in [1] 408 abort (core dumped) ./gdb -nx -ex "set debug python 1" After having created the inferiors object, their refcount is 1 (which comes from PyObject_New), but it should be two. The gdb inferior object has a reference and the "infs" list has a reference. When invoking remove-inferiors, py_free_inferior gets called. It does the decref that corresponds to the reference that the gdb inferior object kept. At this moment, the refcount drops to 0 and the object gets deallocated, even though the "infs" list still has a reference. When we set "infs" to None, Python tries to decref the already zero refcount and the assert triggers. With this patch, it looks better: (gdb) add-inferior Added inferior 2 (gdb) python infs = gdb.inferiors() Creating Python Inferior object inf = 1 Creating Python Inferior object inf = 2 (gdb) remove-inferiors 2 py_free_inferior inf = 2 (gdb) python infs = None infpy_dealloc inf = gdb/ChangeLog: * python/py-inferior.c (inferior_to_inferior_object): Manually increment reference count when creating the object as well. --- gdb/python/py-inferior.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/gdb/python/py-inferior.c b/gdb/python/py-inferior.c index 340dddcfbd..24ef4f0ec8 100644 --- a/gdb/python/py-inferior.c +++ b/gdb/python/py-inferior.c @@ -227,10 +227,13 @@ inferior_to_inferior_object (struct inferior *inferior) inf_obj->threads = NULL; inf_obj->nthreads = 0; + /* PyObject_New initializes the new object with a refcount of 1. This + counts for the reference we are keeping in the inferior data. */ set_inferior_data (inferior, infpy_inf_data_key, inf_obj); } - else - Py_INCREF ((PyObject *)inf_obj); + + /* We are returning a new reference. */ + Py_INCREF (inf_obj); return gdbpy_inf_ref (inf_obj); } -- 2.11.0