From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f69.google.com (mail-pg0-f69.google.com [74.125.83.69]) by kanga.kvack.org (Postfix) with ESMTP id 79BEB6B0005 for ; Tue, 27 Feb 2018 11:59:18 -0500 (EST) Received: by mail-pg0-f69.google.com with SMTP id a26so5355747pgn.18 for ; Tue, 27 Feb 2018 08:59:18 -0800 (PST) Received: from out30-133.freemail.mail.aliyun.com (out30-133.freemail.mail.aliyun.com. [115.124.30.133]) by mx.google.com with ESMTPS id o64si8812565pfb.346.2018.02.27.08.59.16 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 27 Feb 2018 08:59:17 -0800 (PST) Subject: Re: [PATCH 3/4 v2] fs: proc: use down_read_killable() in environ_read() 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 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: owner-linux-mm@kvack.org List-ID: To: Alexey Dobriyan Cc: akpm@linux-foundation.org, mingo@kernel.org, linux-mm@kvack.org, 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); -- 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