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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 77E94C433FF for ; Mon, 29 Jul 2019 20:06:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4C0CE205F4 for ; Mon, 29 Jul 2019 20:06:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564430769; bh=yqk5+woGcvyUKN15EkNQE6LysIPXR3OVtsHCMxiKPWE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=TQ9Lojs+m1+LaU7PBy0Ub270pYr+ebvZZHz7VQDI1KnWHg4OzTFClDo0qg/M1+u/L mq4qPpkQQkyfTTxZXoTqbNxhhgVHDU4v294ctmAUlLuJLhJhDk/1sqV0IrNzATExGA LJ9e9zRoEw8Fri9wviUFphWH66d8NyUMXC2SPQzc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390009AbfG2UGH (ORCPT ); Mon, 29 Jul 2019 16:06:07 -0400 Received: from mail.kernel.org ([198.145.29.99]:57156 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389378AbfG2Tlj (ORCPT ); Mon, 29 Jul 2019 15:41:39 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 7D5D92171F; Mon, 29 Jul 2019 19:41:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564429298; bh=yqk5+woGcvyUKN15EkNQE6LysIPXR3OVtsHCMxiKPWE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=MQM9Wq61JQdc1WtvRb6IhC4pC0H1/cUlpK98Y5TLoK3b8T1yiTvBWFtB7vQhsHBD5 wIj/buPwCmlBNrqGtJE1vo1cS0AG5yY0K3wHh7YuPEP1vXV/47sn4veHrZcw2Lid6M kX7aP1Ic4exjOJEmDU3D2wRgWsKA6qUjzTOxLoFQ= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Johannes Berg , Richard Weinberger , Sasha Levin Subject: [PATCH 4.19 053/113] um: Silence lockdep complaint about mmap_sem Date: Mon, 29 Jul 2019 21:22:20 +0200 Message-Id: <20190729190708.242105787@linuxfoundation.org> X-Mailer: git-send-email 2.22.0 In-Reply-To: <20190729190655.455345569@linuxfoundation.org> References: <20190729190655.455345569@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 [ Upstream commit 80bf6ceaf9310b3f61934c69b382d4912deee049 ] When we get into activate_mm(), lockdep complains that we're doing something strange: WARNING: possible circular locking dependency detected 5.1.0-10252-gb00152307319-dirty #121 Not tainted ------------------------------------------------------ inside.sh/366 is trying to acquire lock: (____ptrval____) (&(&p->alloc_lock)->rlock){+.+.}, at: flush_old_exec+0x703/0x8d7 but task is already holding lock: (____ptrval____) (&mm->mmap_sem){++++}, at: flush_old_exec+0x6c5/0x8d7 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&mm->mmap_sem){++++}: [...] __lock_acquire+0x12ab/0x139f lock_acquire+0x155/0x18e down_write+0x3f/0x98 flush_old_exec+0x748/0x8d7 load_elf_binary+0x2ca/0xddb [...] -> #0 (&(&p->alloc_lock)->rlock){+.+.}: [...] __lock_acquire+0x12ab/0x139f lock_acquire+0x155/0x18e _raw_spin_lock+0x30/0x83 flush_old_exec+0x703/0x8d7 load_elf_binary+0x2ca/0xddb [...] other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&mm->mmap_sem); lock(&(&p->alloc_lock)->rlock); lock(&mm->mmap_sem); lock(&(&p->alloc_lock)->rlock); *** DEADLOCK *** 2 locks held by inside.sh/366: #0: (____ptrval____) (&sig->cred_guard_mutex){+.+.}, at: __do_execve_file+0x12d/0x869 #1: (____ptrval____) (&mm->mmap_sem){++++}, at: flush_old_exec+0x6c5/0x8d7 stack backtrace: CPU: 0 PID: 366 Comm: inside.sh Not tainted 5.1.0-10252-gb00152307319-dirty #121 Stack: [...] Call Trace: [<600420de>] show_stack+0x13b/0x155 [<6048906b>] dump_stack+0x2a/0x2c [<6009ae64>] print_circular_bug+0x332/0x343 [<6009c5c6>] check_prev_add+0x669/0xdad [<600a06b4>] __lock_acquire+0x12ab/0x139f [<6009f3d0>] lock_acquire+0x155/0x18e [<604a07e0>] _raw_spin_lock+0x30/0x83 [<60151e6a>] flush_old_exec+0x703/0x8d7 [<601a8eb8>] load_elf_binary+0x2ca/0xddb [...] I think it's because in exec_mmap() we have down_read(&old_mm->mmap_sem); ... task_lock(tsk); ... activate_mm(active_mm, mm); (which does down_write(&mm->mmap_sem)) I'm not really sure why lockdep throws in the whole knowledge about the task lock, but it seems that old_mm and mm shouldn't ever be the same (and it doesn't deadlock) so tell lockdep that they're different. Signed-off-by: Johannes Berg Signed-off-by: Richard Weinberger Signed-off-by: Sasha Levin --- arch/um/include/asm/mmu_context.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/um/include/asm/mmu_context.h b/arch/um/include/asm/mmu_context.h index fca34b2177e2..129fb1d1f1c5 100644 --- a/arch/um/include/asm/mmu_context.h +++ b/arch/um/include/asm/mmu_context.h @@ -53,7 +53,7 @@ static inline void activate_mm(struct mm_struct *old, struct mm_struct *new) * when the new ->mm is used for the first time. */ __switch_mm(&new->context.id); - down_write(&new->mmap_sem); + down_write_nested(&new->mmap_sem, 1); uml_setup_stubs(new); up_write(&new->mmap_sem); } -- 2.20.1