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=-8.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 C160FC282C8 for ; Mon, 28 Jan 2019 16:45:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 86F202084C for ; Mon, 28 Jan 2019 16:45:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="rIzslTGd" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389965AbfA1QpG (ORCPT ); Mon, 28 Jan 2019 11:45:06 -0500 Received: from mail-qt1-f193.google.com ([209.85.160.193]:33486 "EHLO mail-qt1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389113AbfA1QpF (ORCPT ); Mon, 28 Jan 2019 11:45:05 -0500 Received: by mail-qt1-f193.google.com with SMTP id l11so18996478qtp.0 for ; Mon, 28 Jan 2019 08:45:05 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=yX0lx2enEm0ho3MBCT9f8E7DZGiastAJR1EiGt/PD+g=; b=rIzslTGdanb2OhJ9WsCE0cZo8ngvCLC8GljHWKMvGCk9qg1D5X4UdljVEUy/4ID7XD pN7hkaGuI44+ldFu7cZkRaMnA3H7iJ2fC5leWHfMwOAsTYdhtdT2bsa12XNWGpUqovPa aS4OIUW5iJfsGvLIMhUwQb/MCjclMt1ydLrDY= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=yX0lx2enEm0ho3MBCT9f8E7DZGiastAJR1EiGt/PD+g=; b=mWdb47Cv0CNMDJ53Rp6TsQJA5flS2wPOxAJLcqL5Nt+NJ31lIJMa7M2Qd9ZACFYD/E dIuLPwu76S/et02csHYs0AChW0kKAdKoqX1iD4HTCWZggcX8Rt7UePh92GzSrdMhDb2t rvWKOMY5eNMTenAugxWWR03FLCCOqka5E7G7a4duR5lWD1K+f8LwaS/T7LUKovLOXjDd r16nldr3sdg0LsBCMZJpNDhn6nNCwzy9kN/lOtAkXlxm/x5CNv3zNJ7Jgk/1UR6N9S63 bVW/fKZSfunJGjd/Z066/3+VWsBsNrCeCK7G3xRmYfqIc8Hz+qQ8Oz8QOBoL4Vb+XFtk DsOw== X-Gm-Message-State: AJcUukdvLGIYQo1gLCfmoqcbqFvM7eLuR1ORtE5Apss/JXQTdOWWEMYF Ud09uckShlNMGSwkqJLCahDnPA== X-Google-Smtp-Source: ALg8bN6Okkn6VGO5VUPUUEjc8DtkIfFV+RPv0Hatm7QLi5IsmcbGh/a89HRckacmq69QyFBHCWHMUA== X-Received: by 2002:aed:30c4:: with SMTP id 62mr21276888qtf.290.1548693904561; Mon, 28 Jan 2019 08:45:04 -0800 (PST) Received: from localhost ([2620:0:1004:1100:cca9:fccc:8667:9bdc]) by smtp.gmail.com with ESMTPSA id p42sm79595432qte.8.2019.01.28.08.45.03 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 28 Jan 2019 08:45:03 -0800 (PST) Date: Mon, 28 Jan 2019 11:45:02 -0500 From: Joel Fernandes To: Tetsuo Handa Cc: Andrew Morton , Todd Kjos , syzbot+a76129f18c89f3e2ddd4@syzkaller.appspotmail.com, ak@linux.intel.com, Johannes Weiner , jack@suse.cz, jrdr.linux@gmail.com, LKML , linux-mm@kvack.org, mawilcox@microsoft.com, mgorman@techsingularity.net, syzkaller-bugs@googlegroups.com, Arve =?iso-8859-1?B?SGr4bm5lduVn?= , Todd Kjos , Martijn Coenen , Greg Kroah-Hartman Subject: Re: possible deadlock in __do_page_fault Message-ID: <20190128164502.GA260885@google.com> References: <201901230201.x0N214eq043832@www262.sakura.ne.jp> <20190123155751.GA168927@google.com> <201901240152.x0O1qUUU069046@www262.sakura.ne.jp> <20190124134646.GA53008@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 26, 2019 at 01:02:06AM +0900, Tetsuo Handa wrote: > On 2019/01/24 22:46, Joel Fernandes wrote: > > On Thu, Jan 24, 2019 at 10:52:30AM +0900, Tetsuo Handa wrote: > >> Joel Fernandes wrote: > >>>> Anyway, I need your checks regarding whether this approach is waiting for > >>>> completion at all locations which need to wait for completion. > >>> > >>> I think you are waiting in unwanted locations. The only location you need to > >>> wait in is ashmem_pin_unpin. > >>> > >>> So, to my eyes all that is needed to fix this bug is: > >>> > >>> 1. Delete the range from the ashmem_lru_list > >>> 2. Release the ashmem_mutex > >>> 3. fallocate the range. > >>> 4. Do the completion so that any waiting pin/unpin can proceed. > >>> > >>> Could you clarify why you feel you need to wait for completion at those other > >>> locations? > > OK. Here is an updated patch. > Passed syzbot's best-effort testing using reproducers on all three reports. > > From f192176dbee54075d41249e9f22918c32cb4d4fc Mon Sep 17 00:00:00 2001 > From: Tetsuo Handa > Date: Fri, 25 Jan 2019 23:43:01 +0900 > Subject: [PATCH] staging: android: ashmem: Don't call fallocate() with ashmem_mutex held. > > syzbot is hitting lockdep warnings [1][2][3]. This patch tries to fix > the warning by eliminating ashmem_shrink_scan() => {shmem|vfs}_fallocate() > sequence. > > [1] https://syzkaller.appspot.com/bug?id=87c399f6fa6955006080b24142e2ce7680295ad4 > [2] https://syzkaller.appspot.com/bug?id=7ebea492de7521048355fc84210220e1038a7908 > [3] https://syzkaller.appspot.com/bug?id=e02419c12131c24e2a957ea050c2ab6dcbbc3270 > > Reported-by: syzbot > Reported-by: syzbot > Reported-by: syzbot > Signed-off-by: Tetsuo Handa > --- > drivers/staging/android/ashmem.c | 23 ++++++++++++++++++----- > 1 file changed, 18 insertions(+), 5 deletions(-) > > diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c > index 90a8a9f..d40c1d2 100644 > --- a/drivers/staging/android/ashmem.c > +++ b/drivers/staging/android/ashmem.c > @@ -75,6 +75,9 @@ struct ashmem_range { > /* LRU list of unpinned pages, protected by ashmem_mutex */ > static LIST_HEAD(ashmem_lru_list); > > +static atomic_t ashmem_shrink_inflight = ATOMIC_INIT(0); > +static DECLARE_WAIT_QUEUE_HEAD(ashmem_shrink_wait); > + > /* > * long lru_count - The count of pages on our LRU list. > * > @@ -438,7 +441,6 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma) > static unsigned long > ashmem_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) > { > - struct ashmem_range *range, *next; > unsigned long freed = 0; > > /* We might recurse into filesystem code, so bail out if necessary */ > @@ -448,17 +450,27 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma) > if (!mutex_trylock(&ashmem_mutex)) > return -1; > > - list_for_each_entry_safe(range, next, &ashmem_lru_list, lru) { > + while (!list_empty(&ashmem_lru_list)) { > + struct ashmem_range *range = > + list_first_entry(&ashmem_lru_list, typeof(*range), lru); > loff_t start = range->pgstart * PAGE_SIZE; > loff_t end = (range->pgend + 1) * PAGE_SIZE; > + struct file *f = range->asma->file; > > - range->asma->file->f_op->fallocate(range->asma->file, > - FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, > - start, end - start); > + get_file(f); > + atomic_inc(&ashmem_shrink_inflight); > range->purged = ASHMEM_WAS_PURGED; > lru_del(range); > > freed += range_size(range); > + mutex_unlock(&ashmem_mutex); > + f->f_op->fallocate(f, > + FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, > + start, end - start); > + fput(f); > + if (atomic_dec_and_test(&ashmem_shrink_inflight)) > + wake_up_all(&ashmem_shrink_wait); > + mutex_lock(&ashmem_mutex); Let us replace mutex_lock with mutex_trylock, as done before the loop? Here is there is an opportunity to not block other ashmem operations. Otherwise LGTM. Also, CC stable. thanks, - Joel