Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933452AbcCIRLv (ORCPT ); Wed, 9 Mar 2016 12:11:51 -0500 Received: from e18.ny.us.ibm.com ([129.33.205.208]:43929 "EHLO e18.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933372AbcCIRLs (ORCPT ); Wed, 9 Mar 2016 12:11:48 -0500 X-IBM-Helo: d01dlp03.pok.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org Date: Wed, 9 Mar 2016 04:18:22 -0800 From: "Paul E. McKenney" To: Davidlohr Bueso Cc: mingo@kernel.org, wangkefeng.wang@huawei.com, peterz@infradead.org, josh@joshtriplett.org, guohanjun@huawei.com, linux-kernel@vger.kernel.org, Davidlohr Bueso Subject: Re: [PATCH 1/2] locktorture: Fix deboosting nil ptr dereferencing Message-ID: <20160309121822.GM3577@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1457507286-653-1-git-send-email-dave@stgolabs.net> <1457507286-653-2-git-send-email-dave@stgolabs.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1457507286-653-2-git-send-email-dave@stgolabs.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16030917-0045-0000-0000-00000391CD47 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3377 Lines: 70 On Tue, Mar 08, 2016 at 11:08:05PM -0800, Davidlohr Bueso wrote: > For the case of rtmutex torturing we will randomly call into the > boost() handler, including upon module exiting when the tasks are > deboosted before stopping. In such cases the task may or may not have > already been boosted, and therefore the NULL being explicitly passed > can occur anywhere. Currently we only assume that the task will is > at a higher prio, and in consequence, dereference a nil pointer. > > This patch fixes the case of a rmmod locktorture exploding while > pounding on the rtmutex lock (partial trace): > > [83317.452251] task: ffff88081026cf80 ti: ffff880816120000 task.ti: ffff880816120000 > [83317.452258] RIP: 0010:[] [] torture_random+0x5/0x60 [torture] > [83317.452261] RSP: 0018:ffff880816123eb0 EFLAGS: 00010206 > [83317.452264] RAX: ffff88081026cf80 RBX: ffff880816bfa630 RCX: 0000000000160d1b > [83317.452267] RDX: 0000000000000000 RSI: 0000000000000202 RDI: 0000000000000000 > [83317.452269] RBP: ffff88081026cf80 R08: 000000000000001f R09: ffff88017c20ca80 > [83317.452271] R10: 0000000000000000 R11: 000000000048c316 R12: ffffffffa05d1840 > [83317.452273] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 > [83317.452275] FS: 0000000000000000(0000) GS:ffff88203f880000(0000) knlGS:0000000000000000 > [83317.452277] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [83317.452279] CR2: 0000000000000008 CR3: 0000000001c0a000 CR4: 00000000000406e0 > [83317.452281] Stack: > [83317.452288] ffffffffa05d141d ffff880816bfa630 ffffffffa05d1922 ffff88081e70c2c0 > [83317.452295] ffff880816bfa630 ffffffff81095fed 0000000000000000 ffffffff8107bf60 > [83317.452297] ffff880816bfa630 ffffffff00000000 ffff880800000000 ffff880816123f08 > [83317.452297] Call Trace: > [83317.452309] [] torture_rtmutex_boost+0x1d/0x90 [locktorture] > [83317.452315] [] lock_torture_writer+0xe2/0x170 [locktorture] > [83317.452321] [] kthread+0xbd/0xe0 > [83317.452325] [] ret_from_fork+0x3f/0x70 > > This patch ensures that if the random state pointer is not nil and current > is not boosted, then do nothing. > > Signed-off-by: Davidlohr Bueso Queued for 4.7, thank you!!! (If you need it earlier, please let me know.) Thanx, Paul > --- > kernel/locking/locktorture.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c > index 8ef1919d63b2..9e9c5f454f5c 100644 > --- a/kernel/locking/locktorture.c > +++ b/kernel/locking/locktorture.c > @@ -394,12 +394,12 @@ static void torture_rtmutex_boost(struct torture_random_state *trsp) > > if (!rt_task(current)) { > /* > - * (1) Boost priority once every ~50k operations. When the > + * Boost priority once every ~50k operations. When the > * task tries to take the lock, the rtmutex it will account > * for the new priority, and do any corresponding pi-dance. > */ > - if (!(torture_random(trsp) % > - (cxt.nrealwriters_stress * factor))) { > + if (trsp && !(torture_random(trsp) % > + (cxt.nrealwriters_stress * factor))) { > policy = SCHED_FIFO; > param.sched_priority = MAX_RT_PRIO - 1; > } else /* common case, do nothing */ > -- > 2.1.4 >