From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AG47ELuuDWAiCGMHMsBnrx96piuULqIrz6CU9vv5do3xqSNOxlVzpaKmj9Y6tu40y1GuMdHUgIY4 ARC-Seal: i=1; a=rsa-sha256; t=1521222637; cv=none; d=google.com; s=arc-20160816; b=KJO5nO5TIQ9tjoT8uQDVZ89ikGHYIGYLxTzucACYEStdEZdsL/+FC6nlu47G2W5Xbz 7TBjPpOC1Zd4fNT4j4BEv0xEF4D833662d1snDhY43wSSWkdU8NB3SdOgYZpGpRGN6xO ql3GHnqF+UzZLmHGgcCzTWLrD8kkEJeV/e9j07niWLw5AWf+Pjzg1YobItlb2VzQSQYa fJXlpjB6dfww7Ifa/LH/HveZrnEOdxcNKLR9ZG+209+w2CztCjupbDclJ50soahY5F9F pFKhv3aewvRXAkX7FA2AXkNHRWSX4HdPVgelX0CHLkiVFfezg1Ez/ryHl8ODor0pBlaH STaA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-transfer-encoding :content-disposition:mime-version:references:message-id:subject:cc :to:from:date:arc-authentication-results; bh=G49CLIrvhU/L2R75PTWrJILQu3VW3lWD0CCBRbmrR3E=; b=tz1210NfxXeY73jfCs5B+89GjhAW0KohBB+2IvsLp5JvoB0v/s54QRShUoWFIXKb0x bEyQar8gXxW+DUa8ufM5Cvs44ePBRAPInS604UU9wOq23CD7wuMQ/gR1uB/cUK53JssC RkB6Pn5CZn0j1pXQ/xxOoYxl7qyg54TuBLXIBGNFQwGNEhg57OTvS037MJirkPH8Czrq K0Qd0Td0SKC/0l5L8wr4phbKCvZ3Zs/vhr520P2IETo0xgxoEMjbEt/nyA7IZTL5GBf7 n1T45ACymUWVwMcdyAoPxXeMDEEz+GbG4wo3VyiUkbhuMFkDpPfdys0CMDNqWbugP7YM ZsIQ== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of oleg@redhat.com designates 66.187.233.73 as permitted sender) smtp.mailfrom=oleg@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Authentication-Results: mx.google.com; spf=pass (google.com: domain of oleg@redhat.com designates 66.187.233.73 as permitted sender) smtp.mailfrom=oleg@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Date: Fri, 16 Mar 2018 18:50:30 +0100 From: Oleg Nesterov To: Ravi Bangoria Cc: mhiramat@kernel.org, peterz@infradead.org, srikar@linux.vnet.ibm.com, acme@kernel.org, ananth@linux.vnet.ibm.com, akpm@linux-foundation.org, alexander.shishkin@linux.intel.com, alexis.berlemont@gmail.com, corbet@lwn.net, dan.j.williams@intel.com, gregkh@linuxfoundation.org, huawei.libin@huawei.com, hughd@google.com, jack@suse.cz, jglisse@redhat.com, jolsa@redhat.com, kan.liang@intel.com, kirill.shutemov@linux.intel.com, kjlx@templeofstupid.com, kstewart@linuxfoundation.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@suse.com, milian.wolff@kdab.com, mingo@redhat.com, namhyung@kernel.org, naveen.n.rao@linux.vnet.ibm.com, pc@us.ibm.com, pombredanne@nexb.com, rostedt@goodmis.org, tglx@linutronix.de, tmricht@linux.vnet.ibm.com, willy@infradead.org, yao.jin@linux.intel.com, fengguang.wu@intel.com Subject: Re: [PATCH 6/8] trace_uprobe/sdt: Fix multiple update of same reference counter Message-ID: <20180316175030.GA28770@redhat.com> References: <20180313125603.19819-1-ravi.bangoria@linux.vnet.ibm.com> <20180313125603.19819-7-ravi.bangoria@linux.vnet.ibm.com> <20180315144959.GB19643@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1594827186487084438?= X-GMAIL-MSGID: =?utf-8?q?1595117548223200238?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On 03/16, Ravi Bangoria wrote: > > On 03/15/2018 08:19 PM, Oleg Nesterov wrote: > > On 03/13, Ravi Bangoria wrote: > >> For tiny binaries/libraries, different mmap regions points to the > >> same file portion. In such cases, we may increment reference counter > >> multiple times. > > Yes, > > > >> But while de-registration, reference counter will get > >> decremented only by once > > could you explain why this happens? sdt_increment_ref_ctr() and > > sdt_decrement_ref_ctr() look symmetrical, _decrement_ should see > > the same mappings? ... >     # strace -o out python >       mmap(NULL, 2738968, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fff92460000 >       mmap(0x7fff926a0000, 327680, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x230000) = 0x7fff926a0000 >       mprotect(0x7fff926a0000, 65536, PROT_READ) = 0 Ah, in this case everything is clear, thanks. I was confused by the changelog, I misinterpreted it as if inc/dec are not balanced in case of multiple mappings even if the application doesn't play with mmap/mprotect/etc. And it seems that you are trying to confuse yourself, not only me ;) Just suppose that an application does mmap+munmap in a loop and the mapped region contains uprobe but not the counter. And this all makes me think that we should do something else. Ideally, install_breakpoint() and remove_breakpoint() should inc/dec the counter if they do not fail... Btw, why do we need a counter, not a boolean? Who else can modify it? Or different uprobes can share the same counter? Oleg.