From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754199AbaETTe5 (ORCPT ); Tue, 20 May 2014 15:34:57 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:34140 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750807AbaETTez (ORCPT ); Tue, 20 May 2014 15:34:55 -0400 Date: Tue, 20 May 2014 12:34:53 -0700 From: Andrew Morton To: Mel Gorman Cc: Johannes Weiner , Vlastimil Babka , Jan Kara , Michal Hocko , Hugh Dickins , Peter Zijlstra , Dave Hansen , Linux Kernel , Linux-MM , Linux-FSDevel , Prabhakar Lad Subject: Re: [PATCH] mm: non-atomically mark page accessed during page cache allocation where possible -fix Message-Id: <20140520123453.09a76dd0c8fad40082a16289@linux-foundation.org> In-Reply-To: <20140520154900.GO23991@suse.de> References: <1399974350-11089-1-git-send-email-mgorman@suse.de> <1399974350-11089-19-git-send-email-mgorman@suse.de> <20140520154900.GO23991@suse.de> X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 20 May 2014 16:49:00 +0100 Mel Gorman wrote: > Prabhakar Lad reported the following problem > > I see following issue on DA850 evm, > git bisect points me to > commit id: 975c3a671f11279441006a29a19f55ccc15fb320 > ( mm: non-atomically mark page accessed during page cache allocation > where possible) > > Unable to handle kernel paging request at virtual address 30e03501 > pgd = c68cc000 > [30e03501] *pgd=00000000 > Internal error: Oops: 1 [#1] PREEMPT ARM > Modules linked in: > CPU: 0 PID: 1015 Comm: network.sh Not tainted 3.15.0-rc5-00323-g975c3a6 #9 > task: c70c4e00 ti: c73d0000 task.ti: c73d0000 > PC is at init_page_accessed+0xc/0x24 > LR is at shmem_write_begin+0x54/0x60 > pc : [] lr : [] psr: 20000013 > sp : c73d1d90 ip : c73d1da0 fp : c73d1d9c > r10: c73d1dec r9 : 00000000 r8 : 00000000 > r7 : c73d1e6c r6 : c694d7bc r5 : ffffffe4 r4 : c73d1dec > r3 : c73d0000 r2 : 00000001 r1 : 00000000 r0 : 30e03501 > Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user > Control: 0005317f Table: c68cc000 DAC: 00000015 > Process network.sh (pid: 1015, stack limit = 0xc73d01c0) > > pagep is set but not pointing to anywhere valid as it's an uninitialised > stack variable. This patch is a fix to > mm-non-atomically-mark-page-accessed-during-page-cache-allocation-where-possible.patch > > ... > > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -2459,7 +2459,7 @@ ssize_t generic_perform_write(struct file *file, > flags |= AOP_FLAG_UNINTERRUPTIBLE; > > do { > - struct page *page; > + struct page *page = NULL; > unsigned long offset; /* Offset into pagecache page */ > unsigned long bytes; /* Bytes to write to page */ > size_t copied; /* Bytes copied from user */ Well not really. generic_perform_write() only touches *page if ->write_begin() returned "success", which is reasonable behavior. I'd say you mucked up shmem_write_begin() - it runs init_page_accessed() even if shmem_getpage() returned an error. It shouldn't be doing that. This? From: Andrew Morton Subject: mm/shmem.c: don't run init_page_accessed() against an uninitialised pointer If shmem_getpage() returned an error then it didn't necessarily initialise *pagep. So shmem_write_begin() shouldn't be playing with *pagep in this situation. Fixes an oops when "mm: non-atomically mark page accessed during page cache allocation where possible" (quite reasonably) left *pagep uninitialized. Reported-by: Prabhakar Lad Cc: Johannes Weiner Cc: Vlastimil Babka Cc: Jan Kara Cc: Michal Hocko Cc: Hugh Dickins Cc: Peter Zijlstra Cc: Dave Hansen Cc: Mel Gorman Signed-off-by: Andrew Morton --- mm/shmem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff -puN mm/shmem.c~mm-non-atomically-mark-page-accessed-during-page-cache-allocation-where-possiblefix-2 mm/shmem.c --- a/mm/shmem.c~mm-non-atomically-mark-page-accessed-during-page-cache-allocation-where-possiblefix-2 +++ a/mm/shmem.c @@ -1376,7 +1376,7 @@ shmem_write_begin(struct file *file, str struct inode *inode = mapping->host; pgoff_t index = pos >> PAGE_CACHE_SHIFT; ret = shmem_getpage(inode, index, pagep, SGP_WRITE, NULL); - if (*pagep) + if (ret == 0 && *pagep) init_page_accessed(*pagep); return ret; } _