Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753608AbbLNUbl (ORCPT ); Mon, 14 Dec 2015 15:31:41 -0500 Received: from mx1.redhat.com ([209.132.183.28]:47034 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753046AbbLNUbk (ORCPT ); Mon, 14 Dec 2015 15:31:40 -0500 Date: Mon, 14 Dec 2015 15:31:39 -0500 From: Mike Snitzer To: Nikolay Borisov Cc: Tejun Heo , "Linux-Kernel@Vger. Kernel. Org" , SiteGround Operations , Alasdair Kergon , device-mapper development Subject: Re: corruption causing crash in __queue_work Message-ID: <20151214203138.GA2871@redhat.com> References: <20151209160803.GK30240@mtj.duckdns.org> <56685573.1020805@kyup.com> <20151209162744.GN30240@mtj.duckdns.org> <566945A2.1050208@kyup.com> <20151210152901.GR30240@mtj.duckdns.org> <566AF262.8050009@kyup.com> <20151211170805.GT30240@mtj.duckdns.org> <566E80AE.7020502@kyup.com> <20151214153147.GA14957@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4955 Lines: 130 On Mon, Dec 14 2015 at 3:11pm -0500, Nikolay Borisov wrote: > On Mon, Dec 14, 2015 at 5:31 PM, Mike Snitzer wrote: > > On Mon, Dec 14 2015 at 3:41P -0500, > > Nikolay Borisov wrote: > > > >> Had another poke at the backtrace that is produced and here what the > >> delayed_work looks like: > >> > >> crash> struct delayed_work ffff88036772c8c0 > >> struct delayed_work { > >> work = { > >> data = { > >> counter = 1537 > >> }, > >> entry = { > >> next = 0xffff88036772c8c8, > >> prev = 0xffff88036772c8c8 > >> }, > >> func = 0xffffffffa0211a30 > >> }, > >> timer = { > >> entry = { > >> next = 0x0, > >> prev = 0xdead000000200200 > >> }, > >> expires = 4349463655, > >> base = 0xffff88047fd2d602, > >> function = 0xffffffff8106da40 , > >> data = 18446612146934696128, > >> slack = -1, > >> start_pid = -1, > >> start_site = 0x0, > >> start_comm = > >> "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000" > >> }, > >> wq = 0xffff88030cf65400, > >> cpu = 21 > >> } > >> > >> From this it seems that the timer is also cancelled/expired judging by > >> the values in timer -> entry. But then again in dm-thin the pool is > >> first suspended, which implies the following functions were called: > >> > >> cancel_delayed_work(&pool->waker); > >> cancel_delayed_work(&pool->no_space_timeout); > >> flush_workqueue(pool->wq); > >> > >> so at that point dm-thin's workqueue should be empty and it shouldn't be > >> possible to queue any more delayed work. But the crashdump clearly shows > >> that the opposite is happening. So far all of this points to a race > >> condition and inserting some sleeps after umount and after vgchange -Kan > >> (command to disable volume group and suspend, so the cancel_delayed_work > >> is invoked) seems to reduce the frequency of crashes, though it doesn't > >> eliminate them. > > > > 'vgchange -Kan' doesn't suspend the pool before it destroys the device. > > So the cancel_delayed_work()s you referenced aren't applicable. > > Hm, but does it not in fact destroy it. Using the following simple > stap script proves so: > > > probe module("dm_thin_pool").function("__pool_destroy") { > print("=========__pool_destroy======"); > print_backtrace(); > > } > > probe module("dm_thin_pool").function("pool_postsuspend") { > > printf("==== POOL_POSTSUSPEND =====\n"); > print_backtrace(); > > } > > Produces the following backtraces: > > ==== POOL_POSTSUSPEND ===== > 0xffffffffa033ad40 : pool_postsuspend+0x0/0x50 [dm_thin_pool] > 0xffffffff8148a5bf : suspend_targets+0x3f/0x90 [kernel] > 0xffffffff8148a668 : dm_table_postsuspend_targets+0x18/0x20 [kernel] > 0xffffffff814886dc : __dm_destroy+0x17c/0x190 [kernel] > 0xffffffff81488723 : dm_destroy+0x13/0x20 [kernel] > 0xffffffff8148f55a : dev_remove+0xfa/0x130 [kernel] > 0xffffffff8148fe94 : ctl_ioctl+0x1d4/0x2e0 [kernel] > 0xffffffff8148ffb3 : dm_ctl_ioctl+0x13/0x20 [kernel] > 0xffffffff811af3f3 : do_vfs_ioctl+0x73/0x380 [kernel] > 0xffffffff811af792 : sys_ioctl+0x92/0xa0 [kernel] > 0xffffffff8159ae2e : entry_SYSCALL_64_fastpath+0x12/0x71 [kernel] > =========__pool_destroy====== 0xffffffffa033ae20 : > __pool_destroy+0x0/0x110 [dm_thin_pool] > 0xffffffffa033af61 : __pool_dec+0x31/0x50 [dm_thin_pool] > 0xffffffffa033afae : pool_dtr+0x2e/0x70 [dm_thin_pool] > 0xffffffff8148c085 : dm_table_destroy+0x65/0x120 [kernel] > 0xffffffff8148868a : __dm_destroy+0x12a/0x190 [kernel] > 0xffffffff81488723 : dm_destroy+0x13/0x20 [kernel] > 0xffffffff8148f55a : dev_remove+0xfa/0x130 [kernel] > 0xffffffff8148fe94 : ctl_ioctl+0x1d4/0x2e0 [kernel] > 0xffffffff8148ffb3 : dm_ctl_ioctl+0x13/0x20 [kernel] > 0xffffffff811af3f3 : do_vfs_ioctl+0x73/0x380 [kernel] > 0xffffffff811af792 : sys_ioctl+0x92/0xa0 [kernel] > 0xffffffff8159ae2e : entry_SYSCALL_64_fastpath+0x12/0x71 [kernel] > > When I run vgchange -Kan on a volume group. So in __dm_destroy before > dm_table_destroy (which calls pool_dtr) > the device is checked to see if it is suspended, and if not not dm > core would invoke the pre/post suspend hooks, and > this should cause the workqueue to be flushed and in quiescent state. No? > > What am I missing? Nothing, clearly you're right! > > > > Can you try this patch? > > I've scheduled some machines to go online with this patch and > will report back if it changes the situation. Thanks a lot! Shouldn't make any difference given the above. But in that the suspend hooks are used during destroy (if not already suspended): makes this report all the more bizarre. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/