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[198.145.29.99]) by mx.google.com with ESMTPS id b40si978438pla.49.2019.06.12.17.04.30 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 12 Jun 2019 17:04:30 -0700 (PDT) Received-SPF: pass (google.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) client-ip=198.145.29.99; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=PwhK9KDI; spf=pass (google.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org Received: from localhost.localdomain (c-73-223-200-170.hsd1.ca.comcast.net [73.223.200.170]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8381A215EA; Thu, 13 Jun 2019 00:04:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1560384270; bh=NTkyzDj/QTOLghrPG/JLDkCzWtcmWPclnCXZ6csi8dA=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=PwhK9KDIoVeC2KXyMTN6hRechTgZcxmHUKfC6o0xKoyJM52N4EE9Tk90KuatIgf9i 3X905okdRCZm9quqBHQxd1WrrwOO1YuXMgfgt3pkNwWDgP6kbVmVhXk3xT+PbA37ho 198aMxiCu+sXlojynnQhbEz6gXddsNXhRzs7LkF4= Date: Wed, 12 Jun 2019 17:04:29 -0700 From: Andrew Morton To: Andrei Vagin Cc: Konstantin Khlebnikov , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Oleg Nesterov , Matthew Wilcox , Michal Hocko , Cyrill Gorcunov , Kirill Tkhai , Michal =?ISO-8859-1?Q?Koutn=FD?= , Al Viro , Roman Gushchin , Dmitry Safonov Subject: Re: [PATCH v2 5/6] proc: use down_read_killable mmap_sem for /proc/pid/map_files Message-Id: <20190612170429.baaae5fe6d84b864508a3ec5@linux-foundation.org> In-Reply-To: <20190612231426.GA3639@gmail.com> References: <156007465229.3335.10259979070641486905.stgit@buzz> <156007493995.3335.9595044802115356911.stgit@buzz> <20190612231426.GA3639@gmail.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, 12 Jun 2019 16:14:28 -0700 Andrei Vagin wrote: > On Sun, Jun 09, 2019 at 01:09:00PM +0300, Konstantin Khlebnikov wrote: > > Do not stuck forever if something wrong. > > Killable lock allows to cleanup stuck tasks and simplifies investigation. > > This patch breaks the CRIU project, because stat() returns EINTR instead > of ENOENT: > > [root@fc24 criu]# stat /proc/self/map_files/0-0 > stat: cannot stat '/proc/self/map_files/0-0': Interrupted system call > > Here is one inline comment with the fix for this issue. > > > @@ -2107,7 +2113,10 @@ static struct dentry *proc_map_files_lookup(struct inode *dir, > > if (!mm) > > goto out_put_task; > > > > - down_read(&mm->mmap_sem); > > + result = ERR_PTR(-EINTR); > > + if (down_read_killable(&mm->mmap_sem)) > > + goto out_put_mm; > > + > > result = ERR_PTR(-ENOENT); > yes, thanks. --- a/fs/proc/base.c~proc-use-down_read_killable-mmap_sem-for-proc-pid-map_files-fix +++ a/fs/proc/base.c @@ -2117,6 +2117,7 @@ static struct dentry *proc_map_files_loo if (down_read_killable(&mm->mmap_sem)) goto out_put_mm; + result = ERR_PTR(-ENOENT); vma = find_exact_vma(mm, vm_start, vm_end); if (!vma) goto out_no_vma; We started doing this trick of using ret = -EFOO; if (something) goto out; decades ago because it generated slightly better code. I rather doubt whether that's still the case. In fact this: --- a/fs/proc/base.c~a +++ a/fs/proc/base.c @@ -2096,35 +2096,45 @@ static struct dentry *proc_map_files_loo struct dentry *result; struct mm_struct *mm; - result = ERR_PTR(-ENOENT); task = get_proc_task(dir); - if (!task) + if (!task) { + result = ERR_PTR(-ENOENT); goto out; + } - result = ERR_PTR(-EACCES); - if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS)) + if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS)) { + result = ERR_PTR(-EACCES); goto out_put_task; + } - result = ERR_PTR(-ENOENT); - if (dname_to_vma_addr(dentry, &vm_start, &vm_end)) + if (dname_to_vma_addr(dentry, &vm_start, &vm_end)) { + result = ERR_PTR(-ENOENT); goto out_put_task; + } mm = get_task_mm(task); - if (!mm) + if (!mm) { + result = ERR_PTR(-ENOENT); goto out_put_task; + } - result = ERR_PTR(-EINTR); - if (down_read_killable(&mm->mmap_sem)) + if (down_read_killable(&mm->mmap_sem)) { + result = ERR_PTR(-EINTR); goto out_put_mm; + } - result = ERR_PTR(-ENOENT); vma = find_exact_vma(mm, vm_start, vm_end); - if (!vma) + if (!vma) { + result = ERR_PTR(-ENOENT); goto out_no_vma; + } - if (vma->vm_file) + if (vma->vm_file) { result = proc_map_files_instantiate(dentry, task, (void *)(unsigned long)vma->vm_file->f_mode); + } else { + result = ERR_PTR(-ENOENT); + } out_no_vma: up_read(&mm->mmap_sem); makes no change to the generated assembly with gcc-7.2.0. And I do think that the above style is clearer and more reliable, as this bug demonstrates.