From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-la0-f41.google.com (mail-la0-f41.google.com [209.85.215.41]) by kanga.kvack.org (Postfix) with ESMTP id DF8706B0032 for ; Tue, 10 Feb 2015 03:26:11 -0500 (EST) Received: by labgd6 with SMTP id gd6so9637454lab.7 for ; Tue, 10 Feb 2015 00:26:11 -0800 (PST) Received: from mail-lb0-x22e.google.com (mail-lb0-x22e.google.com. [2a00:1450:4010:c04::22e]) by mx.google.com with ESMTPS id wk7si11468742lbb.15.2015.02.10.00.26.09 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 10 Feb 2015 00:26:10 -0800 (PST) Received: by mail-lb0-f174.google.com with SMTP id z11so1052656lbi.5 for ; Tue, 10 Feb 2015 00:26:09 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <54D88D38.9010901@suse.cz> References: <54D87FA8.60408@suse.cz> <54D88D38.9010901@suse.cz> Date: Tue, 10 Feb 2015 12:26:09 +0400 Message-ID: Subject: Re: BUG: stuck on mmap_sem in 3.18.6 From: Konstantin Khlebnikov Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka Cc: "linux-mm@kvack.org" , Linux Kernel Mailing List That was caused by backport of 33692f27597fcab536d7cbbcc8f52905133e4aa7 ("vm: add VM_FAULT_SIGSEGV handling support") into v3.18.y without commit 7fb08eca45270d0ae86e1ad9d39c40b7a55d0190 ("x86: mm: move mmap_sem unlock from mm_fault_error() to caller") which have moved mmap_sem around. On Mon, Feb 9, 2015 at 1:34 PM, Vlastimil Babka wrote: > On 02/09/2015 10:46 AM, Konstantin Khlebnikov wrote: >> On Mon, Feb 9, 2015 at 12:36 PM, Vlastimil Babka wrote: >>> On 02/09/2015 08:14 AM, Konstantin Khlebnikov wrote: >>>> Python was running under ptrace-based sandbox "sydbox" used exherbo >>>> chroot. Kernel: 3.18.6 + my patch "mm: prevent endless growth of >>>> anon_vma hierarchy" (patch seems stable). >>>> >>>> [ 4674.087780] INFO: task python:25873 blocked for more than 120 seconds. >>>> [ 4674.087793] Tainted: G U 3.18.6-zurg+ #158 >>>> [ 4674.087797] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" >>>> disables this message. >>>> [ 4674.087801] python D ffff88041e2d2000 14176 25873 25630 0x00000102 >>>> [ 4674.087817] ffff880286247b68 0000000000000086 ffff8803d5fe6b40 >>>> 0000000000012000 >>>> [ 4674.087824] ffff880286247fd8 0000000000012000 ffff88040c16eb40 >>>> ffff8803d5fe6b40 >>>> [ 4674.087830] 0000000300000003 ffff8803d5fe6b40 ffff880362888e78 >>>> ffff880362888e60 >>>> [ 4674.087836] Call Trace: >>>> [ 4674.087854] [] schedule+0x29/0x70 >>>> [ 4674.087865] [] rwsem_down_write_failed+0x1d5/0x2f0 >>>> [ 4674.087873] [] call_rwsem_down_write_failed+0x13/0x20 >>>> [ 4674.087881] [] ? down_write+0x31/0x50 >>>> [ 4674.087891] [] do_coredump+0x144/0xee0 >>>> [ 4674.087900] [] ? pick_next_task_fair+0x397/0x450 >>>> [ 4674.087909] [] ? __switch_to+0x1d6/0x5f0 >>>> [ 4674.087915] [] ? __schedule+0x3a6/0x880 >>>> [ 4674.087924] [] ? klist_remove+0x40/0xd0 >>>> [ 4674.087932] [] get_signal+0x298/0x6b0 >>>> [ 4674.087940] [] do_signal+0x28/0xbb0 >>>> [ 4674.087946] [] ? do_send_sig_info+0x5d/0x80 >>>> [ 4674.087955] [] do_notify_resume+0x69/0xb0 >>>> [ 4674.087963] [] int_signal+0x12/0x17 >>>> >>>> Maybe this guy did something wrong? >>> >>> Well he has do_coredump on stack, so he did something wrong in userspace? But >>> here he's just waiting on down_write. Unless there's some bug in do_coredump >>> that would lock for read and then for write, without an unlock in between? >> >> I mean khugepaged. This code looks really messy. Maybe it already has >> mmap_sem locked for read and tries to lock it again: > > Yeah it is messy, and incidentally I'm trying to change how it works. But I > didn't find such double lock bug there. > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org