From: Minchan Kim Subject: Re: [BUG?] memory hotplug: include/linux/radix-tree.h:145 invoked rcu_dereference_check() without protection! Date: Fri, 17 Dec 2010 09:04:13 +0900 Message-ID: References: <20101121112611.GB4267@deepthought.bhanu.net> <20101121133024.GF23423@thunk.org> <20101121153949.GD20947@barrios-desktop> <20101121173726.GG23423@thunk.org> <20101122061619.GA2764@linux.vnet.ibm.com> <1291748509.19276.62.camel@thinkpad> <20101208101947.b0646226.kamezawa.hiroyu@jp.fujitsu.com> <1292507421.4885.19.camel@thinkpad> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: KAMEZAWA Hiroyuki , paulmck@linux.vnet.ibm.com, Milton Miller , linux-kernel@vger.kernel.org, linux-mm@vger.kernel.org, linux-ext4@vger.kernel.org, "Ted Ts'o" , Arun Bhanu , Mel Gorman , Andrew Morton , Heiko Carstens , Martin Schwidefsky To: gerald.schaefer@de.ibm.com Return-path: Received: from mail-iy0-f174.google.com ([209.85.210.174]:37617 "EHLO mail-iy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753180Ab0LQAEO convert rfc822-to-8bit (ORCPT ); Thu, 16 Dec 2010 19:04:14 -0500 In-Reply-To: <1292507421.4885.19.camel@thinkpad> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Thu, Dec 16, 2010 at 10:50 PM, Gerald Schaefer wrote: > I got the same warning now after increasing /proc/sys/vm/nr_hugepages= , see > below. Both cases are easily reproducible: memory unplug with big pag= e cache, > or adding large pages during run-time. > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D > [ INFO: suspicious rcu_dereference_check() usage. ] > --------------------------------------------------- > include/linux/radix-tree.h:145 invoked rcu_dereference_check() withou= t protection! > > other info that might help us debug this: > > > rcu_scheduler_active =3D 1, debug_locks =3D 0 > 1 lock held by bash/761: > =A0#0: =A0(&(&inode->i_data.tree_lock)->rlock){..-.-.}, at: [<0000000= 0002263ae>] migrate_page_move_mapping+0x4a/0x2d8 > > stack backtrace: > CPU: 1 Not tainted 2.6.37-rc6 #4 > Process bash (pid: 761, task: 00000000181b5540, ksp: 00000000181bb7f8= ) > 00000000181bb818 00000000181bb798 0000000000000002 0000000000000000 > =A0 =A0 =A0 00000000181bb838 00000000181bb7b0 00000000181bb7b0 000000= 000056bafa > =A0 =A0 =A0 0000000000000000 000000003f42bdf0 0000000000000002 000000= 001c43be30 > =A0 =A0 =A0 000003e00000000d 000003e00000000c 00000000181bb800 000000= 0000000000 > =A0 =A0 =A0 0000000000000000 0000000000100bfa 00000000181bb798 000000= 00181bb7d8 > Call Trace: > ([<0000000000100b02>] show_trace+0xee/0x144) > =A0[<000000000022654e>] migrate_page_move_mapping+0x1ea/0x2d8 > =A0[<0000000000226c80>] migrate_page+0x38/0x68 > =A0[<0000000000226d9a>] move_to_new_page+0xea/0x2bc > =A0[<000000000022785a>] migrate_pages+0x496/0x568 > =A0[<000000000021e24e>] compact_zone+0x432/0x7d8 > =A0[<000000000021e772>] compact_zone_order+0x9e/0xbc > =A0[<000000000021ed52>] try_to_compact_pages+0x1ba/0x24c > =A0[<00000000001e1afa>] __alloc_pages_nodemask+0x86a/0xa64 > =A0[<000000000021c80c>] alloc_fresh_huge_page.clone.2+0x68/0x18c > =A0[<000000000021cc4c>] set_max_huge_pages.clone.0+0xa4/0x1ac > =A0[<000000000021ce06>] hugetlb_sysctl_handler+0xb2/0xcc > =A0[<00000000002a6572>] proc_sys_call_handler+0xe6/0x10c > =A0[<00000000002a65be>] proc_sys_write+0x26/0x34 > =A0[<00000000002336e0>] vfs_write+0xac/0x18c > =A0[<00000000002338bc>] SyS_write+0x58/0xa8 > =A0[<0000000000113976>] sysc_noemu+0x16/0x1c > =A0[<0000020000162edc>] 0x20000162edc > INFO: lockdep is turned off. > > I honestly do not understand 100% why this is a false positive, seein= g that > e.g. find_get_page() will also use radix_tree_deref_slot(), holding o= nly the > rcu_read_lock, while migrate_page_move_mapping() has no rcu_read_lock= () but > the &mapping->tree_lock instead. So I'm not quite sure how to fix thi= s > properly, but simply adding rcu_read_lock/unlock() to the affected co= de paths, > even if it is not necessary for synchronization, would get rid of the= warning, > like in the following patch. Any ideas? In case of anon page, we hold rcu_read_lock in unmap_and_move. The problem is file-backed page. In case of that, we hold lock_page and mapping->tree_lock as update-side lock. So we don't need rcu_read_lock. > > --- > =A0fs/hugetlbfs/inode.c | =A0 =A02 ++ > =A0mm/migrate.c =A0 =A0 =A0 =A0 | =A0 =A04 ++++ > =A02 files changed, 6 insertions(+) > > --- a/fs/hugetlbfs/inode.c > +++ b/fs/hugetlbfs/inode.c > @@ -580,7 +580,9 @@ static int hugetlbfs_migrate_page(struct > =A0{ > =A0 =A0 =A0 =A0int rc; > > + =A0 =A0 =A0 rcu_read_lock(); > =A0 =A0 =A0 =A0rc =3D migrate_huge_page_move_mapping(mapping, newpage= , page); > + =A0 =A0 =A0 rcu_read_unlock(); > =A0 =A0 =A0 =A0if (rc) > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0return rc; > =A0 =A0 =A0 =A0migrate_page_copy(newpage, page); > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -417,7 +417,9 @@ int migrate_page(struct address_space *m > > =A0 =A0 =A0 =A0BUG_ON(PageWriteback(page)); =A0 =A0/* Writeback must = be complete */ > > + =A0 =A0 =A0 rcu_read_lock(); > =A0 =A0 =A0 =A0rc =3D migrate_page_move_mapping(mapping, newpage, pag= e); > + =A0 =A0 =A0 rcu_read_unlock(); > > =A0 =A0 =A0 =A0if (rc) > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0return rc; > @@ -444,7 +446,9 @@ int buffer_migrate_page(struct address_s > > =A0 =A0 =A0 =A0head =3D page_buffers(page); > > + =A0 =A0 =A0 rcu_read_lock(); > =A0 =A0 =A0 =A0rc =3D migrate_page_move_mapping(mapping, newpage, pag= e); > + =A0 =A0 =A0 rcu_read_unlock(); > > =A0 =A0 =A0 =A0if (rc) > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0return rc; > > > How about this? Maybe Paul have better idea. (It's apparently be word-wrapped.) diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h index ab2baa5..135af1e 100644 --- a/include/linux/radix-tree.h +++ b/include/linux/radix-tree.h @@ -146,6 +146,20 @@ static inline void *radix_tree_deref_slot(void **p= slot) } /** + * radix_tree_deref_slot_nocheck - dereference a slot without RC= U check + * @pslot: pointer to slot, returned by radix_tree_lookup_slot + * Returns: item that was stored in that slot with any direct point= er flag + * removed. + * + * This functions works like radix_tree_deref_slot except it doesn't c= heck + * RCU rule. Normally this funcion is used with update-side lock. + * You should use this function very carefully. + */ +static inline void *radix_tree_deref_slot_nocheck(void **pslot) +{ + return rcu_dereference_protected(*pslot, 1); +} +/** * radix_tree_deref_retry - check radix_tree_deref_slot * @arg: pointer returned by radix_tree_deref_slot * Returns: 0 if retry is not required, otherwise retry is required diff --git a/mm/migrate.c b/mm/migrate.c index 2eb2243..5be2841 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -244,7 +244,8 @@ static int migrate_page_move_mapping(struct address_space *mappin expected_count =3D 2 + page_has_private(page); if (page_count(page) !=3D expected_count || - (struct page *)radix_tree_deref_slot(pslot) !=3D= page) { + (struct page *)radix_tree_deref_slot_nocheck(ps= lot) + !=3D page) { spin_unlock_irq(&mapping->tree_lock); return -EAGAIN; } @@ -316,7 +317,8 @@ int migrate_huge_page_move_mapping(struct address_space *mapping, expected_count =3D 2 + page_has_private(page); if (page_count(page) !=3D expected_count || - (struct page *)radix_tree_deref_slot(pslot) !=3D page) { + (struct page *)radix_tree_deref_slot_nocheck(pslot) + !=3D page) { spin_unlock_irq(&mapping->tree_lock); return -EAGAIN; } --=20 Kind regards, Minchan Kim -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html