From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2CB73C11F65 for ; Wed, 30 Jun 2021 10:10:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 142A961D0C for ; Wed, 30 Jun 2021 10:10:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233977AbhF3KNG (ORCPT ); Wed, 30 Jun 2021 06:13:06 -0400 Received: from outbound-smtp15.blacknight.com ([46.22.139.232]:57145 "EHLO outbound-smtp15.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233959AbhF3KNG (ORCPT ); Wed, 30 Jun 2021 06:13:06 -0400 X-Greylist: delayed 340 seconds by postgrey-1.27 at vger.kernel.org; Wed, 30 Jun 2021 06:13:06 EDT Received: from mail.blacknight.com (pemlinmail01.blacknight.ie [81.17.254.10]) by outbound-smtp15.blacknight.com (Postfix) with ESMTPS id 0BA9F1C4450 for ; Wed, 30 Jun 2021 11:04:57 +0100 (IST) Received: (qmail 14405 invoked from network); 30 Jun 2021 10:04:56 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.17.255]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 30 Jun 2021 10:04:56 -0000 Date: Wed, 30 Jun 2021 11:04:55 +0100 From: Mel Gorman To: Dave Chinner Cc: linux-xfs@vger.kernel.org, linux-mm@kvack.org, Michal Hocko Subject: Re: [PATCH 1/3] mm: Add kvrealloc() Message-ID: <20210630100455.GI3840@techsingularity.net> References: <20210630061431.1750745-1-david@fromorbit.com> <20210630061431.1750745-2-david@fromorbit.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20210630061431.1750745-2-david@fromorbit.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Wed, Jun 30, 2021 at 04:14:29PM +1000, Dave Chinner wrote: > From: Dave Chinner > > During log recovery of an XFS filesystem with 64kB directory > buffers, rebuilding a buffer split across two log records results > in a memory allocation warning from krealloc like this: > > xfs filesystem being mounted at /mnt/scratch supports timestamps until 2038 (0x7fffffff) > XFS (dm-0): Unmounting Filesystem > XFS (dm-0): Mounting V5 Filesystem > XFS (dm-0): Starting recovery (logdev: internal) > ------------[ cut here ]------------ > WARNING: CPU: 5 PID: 3435170 at mm/page_alloc.c:3539 get_page_from_freelist+0xdee/0xe40 > ..... > RIP: 0010:get_page_from_freelist+0xdee/0xe40 > Call Trace: > ? complete+0x3f/0x50 > __alloc_pages+0x16f/0x300 > alloc_pages+0x87/0x110 > kmalloc_order+0x2c/0x90 > kmalloc_order_trace+0x1d/0x90 > __kmalloc_track_caller+0x215/0x270 > ? xlog_recover_add_to_cont_trans+0x63/0x1f0 > krealloc+0x54/0xb0 > xlog_recover_add_to_cont_trans+0x63/0x1f0 > xlog_recovery_process_trans+0xc1/0xd0 > xlog_recover_process_ophdr+0x86/0x130 > xlog_recover_process_data+0x9f/0x160 > xlog_recover_process+0xa2/0x120 > xlog_do_recovery_pass+0x40b/0x7d0 > ? __irq_work_queue_local+0x4f/0x60 > ? irq_work_queue+0x3a/0x50 > xlog_do_log_recovery+0x70/0x150 > xlog_do_recover+0x38/0x1d0 > xlog_recover+0xd8/0x170 > xfs_log_mount+0x181/0x300 > xfs_mountfs+0x4a1/0x9b0 > xfs_fs_fill_super+0x3c0/0x7b0 > get_tree_bdev+0x171/0x270 > ? suffix_kstrtoint.constprop.0+0xf0/0xf0 > xfs_fs_get_tree+0x15/0x20 > vfs_get_tree+0x24/0xc0 > path_mount+0x2f5/0xaf0 > __x64_sys_mount+0x108/0x140 > do_syscall_64+0x3a/0x70 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > Essentially, we are taking a multi-order allocation from kmem_alloc() > (which has an open coded no fail, no warn loop) and then > reallocating it out to 64kB using krealloc(__GFP_NOFAIL) and that is > then triggering the above warning. > > This is a regression caused by converting this code from an open > coded no fail/no warn reallocation loop to using __GFP_NOFAIL. > > What we actually need here is kvrealloc(), so that if contiguous > page allocation fails we fall back to vmalloc() and we don't > get nasty warnings happening in XFS. > > Fixes: 771915c4f688 ("xfs: remove kmem_realloc()") > Signed-off-by: Dave Chinner > --- > fs/xfs/xfs_log_recover.c | 2 +- > include/linux/mm.h | 2 ++ > mm/util.c | 15 +++++++++++++++ > 3 files changed, 18 insertions(+), 1 deletion(-) > > diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c > index 1721fce2ec94..fee4fbadea0a 100644 > --- a/fs/xfs/xfs_log_recover.c > +++ b/fs/xfs/xfs_log_recover.c > @@ -2062,7 +2062,7 @@ xlog_recover_add_to_cont_trans( > old_ptr = item->ri_buf[item->ri_cnt-1].i_addr; > old_len = item->ri_buf[item->ri_cnt-1].i_len; > > - ptr = krealloc(old_ptr, len + old_len, GFP_KERNEL | __GFP_NOFAIL); > + ptr = kvrealloc(old_ptr, old_len, len + old_len, GFP_KERNEL); > memcpy(&ptr[old_len], dp, len); > item->ri_buf[item->ri_cnt-1].i_len += len; > item->ri_buf[item->ri_cnt-1].i_addr = ptr; While this is an improvement, note that this still potentially fail if, for example, a vm_struct cannot be allocated for the vmalloc area, a virtual range is not available, or the pages cannot be allocated to back the vmalloc range. The last one is potentially problematic if you look at __vmalloc_node_range and __vmalloc_area_node. vmalloc has changed a lot since I last familiar with the code but I think it should not attempt a high-order allocation for 64K but __vmalloc_area_node will call alloc_pages_node with a GFP mask without __GFP_NOFAIL. In most cases, it may still succeed but it could fail if the system is OOM. Did I miss something? I didn't do a full audit to determine what fallout, if any, there is to ultimately passing __GFP_NOFAIL to kvmalloc although kvmalloc_node explicitly notes that __GFP_NOFAIL is not supported. Adding Michal Hocko to the cc to see if he remembers why __GFP_NOFAIL was problematic. Absent being able to pass in __GFP_NOFAIL to kvmalloc_node, the new helper kvrealloc may need to understand __GFP_NOFAIL, avoid passing it to kvmalloc and indefintiely retry instead to avoid an XFS log recovery hitting a NULL pointer exception when the memcpy is tried :( -- Mel Gorman SUSE Labs