From patchwork Tue Sep 27 08:45:36 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vlastimil Babka X-Patchwork-Id: 9351609 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 5F920600CB for ; Tue, 27 Sep 2016 08:45:59 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 4FC2C28FED for ; Tue, 27 Sep 2016 08:45:59 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 4396F290F5; Tue, 27 Sep 2016 08:45:59 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id A8F0228FED for ; Tue, 27 Sep 2016 08:45:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754122AbcI0Ipz (ORCPT ); Tue, 27 Sep 2016 04:45:55 -0400 Received: from mx2.suse.de ([195.135.220.15]:36739 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753121AbcI0Ipx (ORCPT ); Tue, 27 Sep 2016 04:45:53 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 86810AAD1; Tue, 27 Sep 2016 08:45:51 +0000 (UTC) From: Vlastimil Babka To: Alexander Viro , Andrew Morton Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Michal Hocko , netdev@vger.kernel.org, Eric Dumazet , David Laight , Hillf Danton , Nicholas Piggin , Jason Baron , Vlastimil Babka Subject: [PATCH v3] fs/select: add vmalloc fallback for select(2) Date: Tue, 27 Sep 2016 10:45:36 +0200 Message-Id: <20160927084536.5923-1-vbabka@suse.cz> X-Mailer: git-send-email 2.10.0 In-Reply-To: <20160922164359.9035-1-vbabka@suse.cz> References: <20160922164359.9035-1-vbabka@suse.cz> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP The select(2) syscall performs a kmalloc(size, GFP_KERNEL) where size grows with the number of fds passed. We had a customer report page allocation failures of order-4 for this allocation. This is a costly order, so it might easily fail, as the VM expects such allocation to have a lower-order fallback. Such trivial fallback is vmalloc(), as the memory doesn't have to be physically contiguous and the allocation is temporary for the duration of the syscall only. There were some concerns, whether this would have negative impact on the system by exposing vmalloc() to userspace. Although an excessive use of vmalloc can cause some system wide performance issues - TLB flushes etc. - a large order allocation is not for free either and an excessive reclaim/compaction can have a similar effect. Also note that the size is effectively limited by RLIMIT_NOFILE which defaults to 1024 on the systems I checked. That means the bitmaps will fit well within single page and thus the vmalloc() fallback could be only excercised for processes where root allows a higher limit. Note that the poll(2) syscall seems to use a linked list of order-0 pages, so it doesn't need this kind of fallback. [eric.dumazet@gmail.com: fix failure path logic] [akpm@linux-foundation.org: use proper type for size] Signed-off-by: Vlastimil Babka Acked-by: Michal Hocko --- fs/select.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/fs/select.c b/fs/select.c index 8ed9da50896a..3d4f85defeab 100644 --- a/fs/select.c +++ b/fs/select.c @@ -29,6 +29,7 @@ #include #include #include +#include #include @@ -554,7 +555,7 @@ int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp, fd_set_bits fds; void *bits; int ret, max_fds; - unsigned int size; + size_t size, alloc_size; struct fdtable *fdt; /* Allocate small arguments on the stack to save memory and be faster */ long stack_fds[SELECT_STACK_ALLOC/sizeof(long)]; @@ -581,7 +582,14 @@ int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp, if (size > sizeof(stack_fds) / 6) { /* Not enough space in on-stack array; must use kmalloc */ ret = -ENOMEM; - bits = kmalloc(6 * size, GFP_KERNEL); + if (size > (SIZE_MAX / 6)) + goto out_nofds; + + alloc_size = 6 * size; + bits = kmalloc(alloc_size, GFP_KERNEL|__GFP_NOWARN); + if (!bits && alloc_size > PAGE_SIZE) + bits = vmalloc(alloc_size); + if (!bits) goto out_nofds; } @@ -618,7 +626,7 @@ int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp, out: if (bits != stack_fds) - kfree(bits); + kvfree(bits); out_nofds: return ret; }