Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753803Ab0LQAEQ (ORCPT ); Thu, 16 Dec 2010 19:04:16 -0500 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 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=mGnJpdb8FpoDU6uhHDj74zlGse/qhggQR/j7DzkYj4im3bvfe6qys66JDs1IMD6Rb3 h5eR28C7Zgifojs3hhzrnvHf+3lLh4zn18vltfilS3Z4i/i8qT7OIaopY3x61ss/1wxn /xrr9TycARU2kHdGlBx2Wp8mt7rb7SVO9Ij6E= MIME-Version: 1.0 In-Reply-To: <1292507421.4885.19.camel@thinkpad> 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> Date: Fri, 17 Dec 2010 09:04:13 +0900 Message-ID: Subject: Re: [BUG?] memory hotplug: include/linux/radix-tree.h:145 invoked rcu_dereference_check() without protection! From: Minchan Kim To: gerald.schaefer@de.ibm.com 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 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6521 Lines: 172 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 page cache, > or adding large pages during run-time. > > =================================================== > [ INFO: suspicious rcu_dereference_check() usage. ] > --------------------------------------------------- > include/linux/radix-tree.h:145 invoked rcu_dereference_check() without protection! > > other info that might help us debug this: > > > rcu_scheduler_active = 1, debug_locks = 0 > 1 lock held by bash/761: > ?#0: ?(&(&inode->i_data.tree_lock)->rlock){..-.-.}, at: [<00000000002263ae>] 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 > ? ? ? 00000000181bb838 00000000181bb7b0 00000000181bb7b0 000000000056bafa > ? ? ? 0000000000000000 000000003f42bdf0 0000000000000002 000000001c43be30 > ? ? ? 000003e00000000d 000003e00000000c 00000000181bb800 0000000000000000 > ? ? ? 0000000000000000 0000000000100bfa 00000000181bb798 00000000181bb7d8 > Call Trace: > ([<0000000000100b02>] show_trace+0xee/0x144) > ?[<000000000022654e>] migrate_page_move_mapping+0x1ea/0x2d8 > ?[<0000000000226c80>] migrate_page+0x38/0x68 > ?[<0000000000226d9a>] move_to_new_page+0xea/0x2bc > ?[<000000000022785a>] migrate_pages+0x496/0x568 > ?[<000000000021e24e>] compact_zone+0x432/0x7d8 > ?[<000000000021e772>] compact_zone_order+0x9e/0xbc > ?[<000000000021ed52>] try_to_compact_pages+0x1ba/0x24c > ?[<00000000001e1afa>] __alloc_pages_nodemask+0x86a/0xa64 > ?[<000000000021c80c>] alloc_fresh_huge_page.clone.2+0x68/0x18c > ?[<000000000021cc4c>] set_max_huge_pages.clone.0+0xa4/0x1ac > ?[<000000000021ce06>] hugetlb_sysctl_handler+0xb2/0xcc > ?[<00000000002a6572>] proc_sys_call_handler+0xe6/0x10c > ?[<00000000002a65be>] proc_sys_write+0x26/0x34 > ?[<00000000002336e0>] vfs_write+0xac/0x18c > ?[<00000000002338bc>] SyS_write+0x58/0xa8 > ?[<0000000000113976>] sysc_noemu+0x16/0x1c > ?[<0000020000162edc>] 0x20000162edc > INFO: lockdep is turned off. > > I honestly do not understand 100% why this is a false positive, seeing that > e.g. find_get_page() will also use radix_tree_deref_slot(), holding only 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 this > properly, but simply adding rcu_read_lock/unlock() to the affected code 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. > > --- > ?fs/hugetlbfs/inode.c | ? ?2 ++ > ?mm/migrate.c ? ? ? ? | ? ?4 ++++ > ?2 files changed, 6 insertions(+) > > --- a/fs/hugetlbfs/inode.c > +++ b/fs/hugetlbfs/inode.c > @@ -580,7 +580,9 @@ static int hugetlbfs_migrate_page(struct > ?{ > ? ? ? ?int rc; > > + ? ? ? rcu_read_lock(); > ? ? ? ?rc = migrate_huge_page_move_mapping(mapping, newpage, page); > + ? ? ? rcu_read_unlock(); > ? ? ? ?if (rc) > ? ? ? ? ? ? ? ?return rc; > ? ? ? ?migrate_page_copy(newpage, page); > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -417,7 +417,9 @@ int migrate_page(struct address_space *m > > ? ? ? ?BUG_ON(PageWriteback(page)); ? ?/* Writeback must be complete */ > > + ? ? ? rcu_read_lock(); > ? ? ? ?rc = migrate_page_move_mapping(mapping, newpage, page); > + ? ? ? rcu_read_unlock(); > > ? ? ? ?if (rc) > ? ? ? ? ? ? ? ?return rc; > @@ -444,7 +446,9 @@ int buffer_migrate_page(struct address_s > > ? ? ? ?head = page_buffers(page); > > + ? ? ? rcu_read_lock(); > ? ? ? ?rc = migrate_page_move_mapping(mapping, newpage, page); > + ? ? ? rcu_read_unlock(); > > ? ? ? ?if (rc) > ? ? ? ? ? ? ? ?return 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 **pslot) } /** + * radix_tree_deref_slot_nocheck - dereference a slot without RCU check + * @pslot: pointer to slot, returned by radix_tree_lookup_slot + * Returns: item that was stored in that slot with any direct pointer flag + * removed. + * + * This functions works like radix_tree_deref_slot except it doesn't check + * 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 = 2 + page_has_private(page); if (page_count(page) != expected_count || - (struct page *)radix_tree_deref_slot(pslot) != page) { + (struct page *)radix_tree_deref_slot_nocheck(pslot) + != 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 = 2 + page_has_private(page); if (page_count(page) != expected_count || - (struct page *)radix_tree_deref_slot(pslot) != page) { + (struct page *)radix_tree_deref_slot_nocheck(pslot) + != page) { spin_unlock_irq(&mapping->tree_lock); return -EAGAIN; } -- Kind regards, Minchan Kim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/