From owner-freebsd-current@freebsd.org Tue Aug 4 14:53:20 2015 Return-Path: Delivered-To: freebsd-current@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id CB63E9B30B7 for ; Tue, 4 Aug 2015 14:53:20 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 391808DC for ; Tue, 4 Aug 2015 14:53:20 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kostik@localhost [127.0.0.1]) by kib.kiev.ua (8.15.2/8.15.2) with ESMTPS id t74ErBrt025189 (version=TLSv1 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO); Tue, 4 Aug 2015 17:53:11 +0300 (EEST) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.9.2 kib.kiev.ua t74ErBrt025189 Received: (from kostik@localhost) by tom.home (8.15.2/8.15.2/Submit) id t74ErB0m025188; Tue, 4 Aug 2015 17:53:11 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Tue, 4 Aug 2015 17:53:11 +0300 From: Konstantin Belousov To: Luigi Rizzo Cc: freebsd-current , Stefano Garzarella , Giuseppe Lettieri Subject: Re: proper way to terminate a kthread when the parent process dies ? Message-ID: <20150804145311.GN2072@kib.kiev.ua> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) X-Spam-Status: No, score=-2.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FREEMAIL_FROM,NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.1 X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on tom.home X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 04 Aug 2015 14:53:20 -0000 On Tue, Aug 04, 2015 at 04:38:14PM +0200, Luigi Rizzo wrote: > Hi, > we have a doubt on the proper way to terminate a kernel thread that > has been associated to a user process U within a system call with > > kthread_add( .. , .., p, ... ) > > (p is the struct proc * of the calling process, U) > > When U terminates and goes into kern_exit.c :: exit1() > the kernel thread sees the following conditions: > > P_SHOULDSTOP(td->td_proc) is TRUE > > td->td_flags has TDF_ASTPENDING | TDF_NEEDSUSPCHK set > > We are not sure what is the proper way to terminate > our kernel thread, whose body is the following: > > while (must_run) { // someone will set must_run = 0 > > kthread_suspend_check(); // void > work_or_short_tsleep(); // potentially se > } > kthread_exit(); > > We have seen different ways for the > > 1. if (P_SHOULDSTOP(td->td_proc) > break; // kthread_exit() is called outside the loop > > 2. if (P_SHOULDSTOP(td->td_proc) > thread_suspend_check(0); // which then terminates the thread > // this is done in sys/rpc/svc.c > > We are a bit unsure whether calling the thread_*() function in a kthread > is correct -- but there is an example in the kernel. > > Variants involve locking td->td_proc (but is it necessary ? The process > won't go away until all child threads die), or checking the td_tdflags > instead of the parent process' flags. > > So what is the correct way ? If this is a thread of the normal user process, then it is not a kernel thread, even if it never leaves the kernel mode. You must call thread_suspend_check() in any in-kernel loop to allow the stops and process exit to work.