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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 1064CC282C3 for ; Tue, 22 Jan 2019 10:02:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DAEE020823 for ; Tue, 22 Jan 2019 10:02:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727817AbfAVKCo (ORCPT ); Tue, 22 Jan 2019 05:02:44 -0500 Received: from www262.sakura.ne.jp ([202.181.97.72]:10647 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727274AbfAVKCo (ORCPT ); Tue, 22 Jan 2019 05:02:44 -0500 Received: from fsav103.sakura.ne.jp (fsav103.sakura.ne.jp [27.133.134.230]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id x0MA2fDh093931; Tue, 22 Jan 2019 19:02:41 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav103.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav103.sakura.ne.jp); Tue, 22 Jan 2019 19:02:41 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav103.sakura.ne.jp) Received: from [192.168.1.8] (softbank126126163036.bbtec.net [126.126.163.36]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id x0MA2a1n093797 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NO); Tue, 22 Jan 2019 19:02:41 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Subject: Re: possible deadlock in __do_page_fault To: Andrew Morton , Joel Fernandes Cc: Todd Kjos , Joel Fernandes , 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, =?UTF-8?Q?Arve_Hj=c3=b8nnev=c3=a5g?= , Todd Kjos , Martijn Coenen , Greg Kroah-Hartman References: <000000000000f7a28e057653dc6e@google.com> <20180920141058.4ed467594761e073606eafe2@linux-foundation.org> <20180921162110.e22d09a9e281d194db3c8359@linux-foundation.org> From: Tetsuo Handa Message-ID: <4b0a5f8c-2be2-db38-a70d-8d497cb67665@I-love.SAKURA.ne.jp> Date: Tue, 22 Jan 2019 19:02:35 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20180921162110.e22d09a9e281d194db3c8359@linux-foundation.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/09/22 8:21, Andrew Morton wrote: > On Thu, 20 Sep 2018 19:33:15 -0400 Joel Fernandes wrote: > >> On Thu, Sep 20, 2018 at 5:12 PM Todd Kjos wrote: >>> >>> +Joel Fernandes >>> >>> On Thu, Sep 20, 2018 at 2:11 PM Andrew Morton wrote: >>>> >>>> >>>> Thanks. Let's cc the ashmem folks. >>>> >> >> This should be fixed by https://patchwork.kernel.org/patch/10572477/ >> >> It has Neil Brown's Reviewed-by but looks like didn't yet appear in >> anyone's tree, could Greg take this patch? > > All is well. That went into mainline yesterday, with a cc:stable. > This problem was not fixed at all. Why do we need to call fallocate() synchronously with ashmem_mutex held? Why can't we call fallocate() asynchronously from WQ_MEM_RECLAIM workqueue context so that we can call fallocate() with ashmem_mutex not held? I don't know how ashmem works, but as far as I can guess, offloading is possible as long as other operations which depend on the completion of fallocate() operation (e.g. read()/mmap(), querying/changing pinned status) wait for completion of asynchronous fallocate() operation (like a draft patch shown below is doing). --- drivers/staging/android/ashmem.c | 50 ++++++++++++++++++++++++++++---- 1 file changed, 45 insertions(+), 5 deletions(-) diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c index 90a8a9f1ac7d..1a890c43a10a 100644 --- a/drivers/staging/android/ashmem.c +++ b/drivers/staging/android/ashmem.c @@ -75,6 +75,17 @@ struct ashmem_range { /* LRU list of unpinned pages, protected by ashmem_mutex */ static LIST_HEAD(ashmem_lru_list); +static struct workqueue_struct *ashmem_wq; +static atomic_t ashmem_shrink_inflight = ATOMIC_INIT(0); +static DECLARE_WAIT_QUEUE_HEAD(ashmem_shrink_wait); + +struct ashmem_shrink_work { + struct work_struct work; + struct file *file; + loff_t start; + loff_t end; +}; + /* * long lru_count - The count of pages on our LRU list. * @@ -292,6 +303,7 @@ static ssize_t ashmem_read_iter(struct kiocb *iocb, struct iov_iter *iter) int ret = 0; mutex_lock(&ashmem_mutex); + wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight)); /* If size is not set, or set to 0, always return EOF. */ if (asma->size == 0) @@ -359,6 +371,7 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma) int ret = 0; mutex_lock(&ashmem_mutex); + wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight)); /* user needs to SET_SIZE before mapping */ if (!asma->size) { @@ -421,6 +434,19 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma) return ret; } +static void ashmem_shrink_worker(struct work_struct *work) +{ + struct ashmem_shrink_work *w = container_of(work, typeof(*w), work); + + w->file->f_op->fallocate(w->file, + FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, + w->start, w->end - w->start); + fput(w->file); + kfree(w); + if (atomic_dec_and_test(&ashmem_shrink_inflight)) + wake_up_all(&ashmem_shrink_wait); +} + /* * ashmem_shrink - our cache shrinker, called from mm/vmscan.c * @@ -449,12 +475,18 @@ ashmem_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) return -1; list_for_each_entry_safe(range, next, &ashmem_lru_list, lru) { - loff_t start = range->pgstart * PAGE_SIZE; - loff_t end = (range->pgend + 1) * PAGE_SIZE; + struct ashmem_shrink_work *w = kzalloc(sizeof(*w), GFP_ATOMIC); + + if (!w) + break; + INIT_WORK(&w->work, ashmem_shrink_worker); + w->file = range->asma->file; + get_file(w->file); + w->start = range->pgstart * PAGE_SIZE; + w->end = (range->pgend + 1) * PAGE_SIZE; + atomic_inc(&ashmem_shrink_inflight); + queue_work(ashmem_wq, &w->work); - range->asma->file->f_op->fallocate(range->asma->file, - FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, - start, end - start); range->purged = ASHMEM_WAS_PURGED; lru_del(range); @@ -713,6 +745,7 @@ static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd, return -EFAULT; mutex_lock(&ashmem_mutex); + wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight)); if (!asma->file) goto out_unlock; @@ -883,8 +916,15 @@ static int __init ashmem_init(void) goto out_free2; } + ashmem_wq = alloc_workqueue("ashmem_wq", WQ_MEM_RECLAIM, 0); + if (!ashmem_wq) { + pr_err("failed to create workqueue\n"); + goto out_demisc; + } + ret = register_shrinker(&ashmem_shrinker); if (ret) { + destroy_workqueue(ashmem_wq); pr_err("failed to register shrinker!\n"); goto out_demisc; } -- 2.17.1