From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752023AbeB0Q7Z (ORCPT ); Tue, 27 Feb 2018 11:59:25 -0500 Received: from out30-131.freemail.mail.aliyun.com ([115.124.30.131]:53717 "EHLO out30-131.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751907AbeB0Q7W (ORCPT ); Tue, 27 Feb 2018 11:59:22 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R121e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04421;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=5;SR=0;TI=SMTPD_---0SybBtBx_1519750750; Subject: Re: [PATCH 3/4 v2] fs: proc: use down_read_killable() in environ_read() To: Alexey Dobriyan Cc: akpm@linux-foundation.org, mingo@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1519691151-101999-1-git-send-email-yang.shi@linux.alibaba.com> <1519691151-101999-4-git-send-email-yang.shi@linux.alibaba.com> <20180227071536.GA5234@avx2> From: Yang Shi Message-ID: <140f613b-0214-97bb-9823-0abac394e331@linux.alibaba.com> Date: Tue, 27 Feb 2018 08:59:06 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <20180227071536.GA5234@avx2> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/26/18 11:15 PM, Alexey Dobriyan wrote: > On Tue, Feb 27, 2018 at 08:25:50AM +0800, Yang Shi wrote: >> Like reading /proc/*/cmdline, it is possible to be blocked for long time >> when reading /proc/*/environ when manipulating large mapping at the mean >> time. The environ reading process will be waiting for mmap_sem become >> available for a long time then it may cause the reading task hung. >> >> Convert down_read() and access_remote_vm() to killable version. >> >> Signed-off-by: Yang Shi >> Suggested-by: Alexey Dobriyan > Ehh, bloody tags. I mean fix reading /proc/*/environ part. > I didn't suggest _killable() variants, they're quite ugly because API > multiplies. access_remote_vm() could be converted to down_read_killable(). There might be other places that need non-killable access_remote_vm(), like patch 4/4. And, it sounds keeping access_remote_vm() semantic intact may prevent from confusion. The most people may get used to assume access_remote_vm() behaves like access_process_vm() except not inc mm reference count. Thanks, Yang > >> --- a/fs/proc/base.c >> +++ b/fs/proc/base.c >> @@ -933,7 +933,9 @@ static ssize_t environ_read(struct file *file, char __user *buf, >> if (!mmget_not_zero(mm)) >> goto free; >> >> - down_read(&mm->mmap_sem); >> + ret = down_read_killable(&mm->mmap_sem); >> + if (ret) >> + goto out_mmput; >> env_start = mm->env_start; >> env_end = mm->env_end; >> up_read(&mm->mmap_sem); >> @@ -950,7 +952,8 @@ static ssize_t environ_read(struct file *file, char __user *buf, >> max_len = min_t(size_t, PAGE_SIZE, count); >> this_len = min(max_len, this_len); >> >> - retval = access_remote_vm(mm, (env_start + src), page, this_len, 0); >> + retval = access_remote_vm_killable(mm, (env_start + src), >> + page, this_len, 0);