From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 06D0AC352A3 for ; Mon, 10 Feb 2020 13:33:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C86EB20714 for ; Mon, 10 Feb 2020 13:33:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581341590; bh=2ZF+h9JLW6xwj1g9e5dbPom8XU1N9aszxzb91xGMCo8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=JHhdrCoLcyzoUSp2Q/ZoPbzZJn2c0XUMJgkV36x5zFD0yHeCK7btLd2xJDoeW7Sce /hr4x3LHww0eBy+Q+sIyP0dDeo/yM4nATbPaTrXzlSegjgjEqx1f/hTY7qFcNLTVNQ SKeAzjGpcvw+wYpyRIsV5xQcBkXL8xj0mjHeut24= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731589AbgBJNdJ (ORCPT ); Mon, 10 Feb 2020 08:33:09 -0500 Received: from mail.kernel.org ([198.145.29.99]:53250 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728041AbgBJMfj (ORCPT ); Mon, 10 Feb 2020 07:35:39 -0500 Received: from localhost (unknown [209.37.97.194]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 72466215A4; Mon, 10 Feb 2020 12:35:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581338138; bh=2ZF+h9JLW6xwj1g9e5dbPom8XU1N9aszxzb91xGMCo8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=HPagOBbtSSN12g6D0NloAmSWZ/n5fDztSsimR1lA4ufu0C6qyDgSyn8tlaUW1AsEs HPTp5zQyTsRzEz0aGKEpGXCE8ZCoGzPve9jAVxnHY69U3zKEFOu50z+nYSY8KGydkJ poSR92M9ENXn/g5bvbXAoxG3ImPt0ToA+t7TxDs4= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Dan Williams , Michal Hocko , David Hildenbrand , Vishal Verma , Pavel Tatashin , Dave Hansen , Andrew Morton , Linus Torvalds Subject: [PATCH 4.19 038/195] mm/memory_hotplug: fix remove_memory() lockdep splat Date: Mon, 10 Feb 2020 04:31:36 -0800 Message-Id: <20200210122310.174718077@linuxfoundation.org> X-Mailer: git-send-email 2.25.0 In-Reply-To: <20200210122305.731206734@linuxfoundation.org> References: <20200210122305.731206734@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dan Williams commit f1037ec0cc8ac1a450974ad9754e991f72884f48 upstream. The daxctl unit test for the dax_kmem driver currently triggers the (false positive) lockdep splat below. It results from the fact that remove_memory_block_devices() is invoked under the mem_hotplug_lock() causing lockdep entanglements with cpu_hotplug_lock() and sysfs (kernfs active state tracking). It is a false positive because the sysfs attribute path triggering the memory remove is not the same attribute path associated with memory-block device. sysfs_break_active_protection() is not applicable since there is no real deadlock conflict, instead move memory-block device removal outside the lock. The mem_hotplug_lock() is not needed to synchronize the memory-block device removal vs the page online state, that is already handled by lock_device_hotplug(). Specifically, lock_device_hotplug() is sufficient to allow try_remove_memory() to check the offline state of the memblocks and be assured that any in progress online attempts are flushed / blocked by kernfs_drain() / attribute removal. The add_memory() path safely creates memblock devices under the mem_hotplug_lock(). There is no kernfs active state synchronization in the memblock device_register() path, so nothing to fix there. This change is only possible thanks to the recent change that refactored memory block device removal out of arch_remove_memory() (commit 4c4b7f9ba948 "mm/memory_hotplug: remove memory block devices before arch_remove_memory()"), and David's due diligence tracking down the guarantees afforded by kernfs_drain(). Not flagged for -stable since this only impacts ongoing development and lockdep validation, not a runtime issue. ====================================================== WARNING: possible circular locking dependency detected 5.5.0-rc3+ #230 Tainted: G OE ------------------------------------------------------ lt-daxctl/6459 is trying to acquire lock: ffff99c7f0003510 (kn->count#241){++++}, at: kernfs_remove_by_name_ns+0x41/0x80 but task is already holding lock: ffffffffa76a5450 (mem_hotplug_lock.rw_sem){++++}, at: percpu_down_write+0x20/0xe0 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (mem_hotplug_lock.rw_sem){++++}: __lock_acquire+0x39c/0x790 lock_acquire+0xa2/0x1b0 get_online_mems+0x3e/0xb0 kmem_cache_create_usercopy+0x2e/0x260 kmem_cache_create+0x12/0x20 ptlock_cache_init+0x20/0x28 start_kernel+0x243/0x547 secondary_startup_64+0xb6/0xc0 -> #1 (cpu_hotplug_lock.rw_sem){++++}: __lock_acquire+0x39c/0x790 lock_acquire+0xa2/0x1b0 cpus_read_lock+0x3e/0xb0 online_pages+0x37/0x300 memory_subsys_online+0x17d/0x1c0 device_online+0x60/0x80 state_store+0x65/0xd0 kernfs_fop_write+0xcf/0x1c0 vfs_write+0xdb/0x1d0 ksys_write+0x65/0xe0 do_syscall_64+0x5c/0xa0 entry_SYSCALL_64_after_hwframe+0x49/0xbe -> #0 (kn->count#241){++++}: check_prev_add+0x98/0xa40 validate_chain+0x576/0x860 __lock_acquire+0x39c/0x790 lock_acquire+0xa2/0x1b0 __kernfs_remove+0x25f/0x2e0 kernfs_remove_by_name_ns+0x41/0x80 remove_files.isra.0+0x30/0x70 sysfs_remove_group+0x3d/0x80 sysfs_remove_groups+0x29/0x40 device_remove_attrs+0x39/0x70 device_del+0x16a/0x3f0 device_unregister+0x16/0x60 remove_memory_block_devices+0x82/0xb0 try_remove_memory+0xb5/0x130 remove_memory+0x26/0x40 dev_dax_kmem_remove+0x44/0x6a [kmem] device_release_driver_internal+0xe4/0x1c0 unbind_store+0xef/0x120 kernfs_fop_write+0xcf/0x1c0 vfs_write+0xdb/0x1d0 ksys_write+0x65/0xe0 do_syscall_64+0x5c/0xa0 entry_SYSCALL_64_after_hwframe+0x49/0xbe other info that might help us debug this: Chain exists of: kn->count#241 --> cpu_hotplug_lock.rw_sem --> mem_hotplug_lock.rw_sem Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(mem_hotplug_lock.rw_sem); lock(cpu_hotplug_lock.rw_sem); lock(mem_hotplug_lock.rw_sem); lock(kn->count#241); *** DEADLOCK *** No fixes tag as this has been a long standing issue that predated the addition of kernfs lockdep annotations. Link: http://lkml.kernel.org/r/157991441887.2763922.4770790047389427325.stgit@dwillia2-desk3.amr.corp.intel.com Signed-off-by: Dan Williams Acked-by: Michal Hocko Reviewed-by: David Hildenbrand Cc: Vishal Verma Cc: Pavel Tatashin Cc: Dave Hansen Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/memory_hotplug.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -1902,8 +1902,6 @@ void __ref __remove_memory(int nid, u64 BUG_ON(check_hotplug_memory_range(start, size)); - mem_hotplug_begin(); - /* * All memory blocks must be offlined before removing memory. Check * whether all memory blocks in question are offline and trigger a BUG() @@ -1919,9 +1917,14 @@ void __ref __remove_memory(int nid, u64 memblock_free(start, size); memblock_remove(start, size); - /* remove memory block devices before removing memory */ + /* + * Memory block device removal under the device_hotplug_lock is + * a barrier against racing online attempts. + */ remove_memory_block_devices(start, size); + mem_hotplug_begin(); + arch_remove_memory(nid, start, size, NULL); __release_memory_resource(start, size);