From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759050Ab3E1ESA (ORCPT ); Tue, 28 May 2013 00:18:00 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:52467 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758762Ab3E1Dy2 (ORCPT ); Mon, 27 May 2013 23:54:28 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Alasdair G Kergon" , "Mikulas Patocka" Date: Tue, 28 May 2013 04:49:53 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [25/94] dm bufio: avoid a possible __vmalloc deadlock In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.101 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.46-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Mikulas Patocka commit 502624bdad3dba45dfaacaf36b7d83e39e74b2d2 upstream. This patch uses memalloc_noio_save to avoid a possible deadlock in dm-bufio. (it could happen only with large block size, at most PAGE_SIZE << MAX_ORDER (typically 8MiB). __vmalloc doesn't fully respect gfp flags. The specified gfp flags are used for allocation of requested pages, structures vmap_area, vmap_block and vm_struct and the radix tree nodes. However, the kernel pagetables are allocated always with GFP_KERNEL. Thus the allocation of pagetables can recurse back to the I/O layer and cause a deadlock. This patch uses the function memalloc_noio_save to set per-process PF_MEMALLOC_NOIO flag and the function memalloc_noio_restore to restore it. When this flag is set, all allocations in the process are done with implied GFP_NOIO flag, thus the deadlock can't happen. This should be backported to stable kernels, but they don't have the PF_MEMALLOC_NOIO flag and memalloc_noio_save/memalloc_noio_restore functions. So, PF_MEMALLOC should be set and restored instead. Signed-off-by: Mikulas Patocka Signed-off-by: Alasdair G Kergon [bwh: Backported to 3.2 as recommended] Signed-off-by: Ben Hutchings --- drivers/md/dm-bufio.c | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-) --- a/drivers/md/dm-bufio.c +++ b/drivers/md/dm-bufio.c @@ -322,6 +322,9 @@ static void __cache_size_refresh(void) static void *alloc_buffer_data(struct dm_bufio_client *c, gfp_t gfp_mask, enum data_mode *data_mode) { + unsigned noio_flag; + void *ptr; + if (c->block_size <= DM_BUFIO_BLOCK_SIZE_SLAB_LIMIT) { *data_mode = DATA_MODE_SLAB; return kmem_cache_alloc(DM_BUFIO_CACHE(c), gfp_mask); @@ -335,7 +338,28 @@ static void *alloc_buffer_data(struct dm } *data_mode = DATA_MODE_VMALLOC; - return __vmalloc(c->block_size, gfp_mask, PAGE_KERNEL); + + /* + * __vmalloc allocates the data pages and auxiliary structures with + * gfp_flags that were specified, but pagetables are always allocated + * with GFP_KERNEL, no matter what was specified as gfp_mask. + * + * Consequently, we must set per-process flag PF_MEMALLOC_NOIO so that + * all allocations done by this process (including pagetables) are done + * as if GFP_NOIO was specified. + */ + + if (gfp_mask & __GFP_NORETRY) { + noio_flag = current->flags & PF_MEMALLOC; + current->flags |= PF_MEMALLOC; + } + + ptr = __vmalloc(c->block_size, gfp_mask, PAGE_KERNEL); + + if (gfp_mask & __GFP_NORETRY) + current->flags = (current->flags & ~PF_MEMALLOC) | noio_flag; + + return ptr; } /*