From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx199.postini.com [74.125.245.199]) by kanga.kvack.org (Postfix) with SMTP id 4D4416B0071 for ; Fri, 4 Jan 2013 19:35:50 -0500 (EST) Date: Sat, 5 Jan 2013 01:35:45 +0100 (CET) From: Jiri Kosina Subject: [PATCH 2/2] mm: mmap: annotate vm_lock_anon_vma locking properly for lockdep In-Reply-To: Message-ID: References: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Rik van Riel , Ingo Molnar , Peter Zijlstra , Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org Commit 5a505085f04 ("mm/rmap: Convert the struct anon_vma::mutex to an rwsem") turned anon_vma mutex to rwsem. However, the properly annotated nested locking in mm_take_all_locks() has been converted from mutex_lock_nest_lock(&anon_vma->root->mutex, &mm->mmap_sem); to down_write(&anon_vma->root->rwsem); which is incomplete, and causes the false positive report from lockdep below. Annotate the fact that mmap_sem is used as an outter lock to serialize taking of all the anon_vma rwsems at once no matter the order, using the down_write_nest_lock() primitive. This patch fixes this lockdep report: ============================================= [ INFO: possible recursive locking detected ] 3.8.0-rc2-00036-g5f73896 #171 Not tainted --------------------------------------------- qemu-kvm/2315 is trying to acquire lock: (&anon_vma->rwsem){+.+...}, at: [] mm_take_all_locks+0x149/0x1b0 but task is already holding lock: (&anon_vma->rwsem){+.+...}, at: [] mm_take_all_locks+0x149/0x1b0 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(&anon_vma->rwsem); lock(&anon_vma->rwsem); *** DEADLOCK *** May be due to missing lock nesting notation 4 locks held by qemu-kvm/2315: #0: (&mm->mmap_sem){++++++}, at: [] do_mmu_notifier_register+0xfc/0x170 #1: (mm_all_locks_mutex){+.+...}, at: [] mm_take_all_locks+0x36/0x1b0 #2: (&mapping->i_mmap_mutex){+.+...}, at: [] mm_take_all_locks+0xc9/0x1b0 #3: (&anon_vma->rwsem){+.+...}, at: [] mm_take_all_locks+0x149/0x1b0 stack backtrace: Pid: 2315, comm: qemu-kvm Not tainted 3.8.0-rc2-00036-g5f73896 #171 Call Trace: [] print_deadlock_bug+0xf2/0x100 [] validate_chain+0x4f6/0x720 [] __lock_acquire+0x359/0x580 [] ? trace_hardirqs_on_caller+0x12d/0x1b0 [] lock_acquire+0x121/0x190 [] ? mm_take_all_locks+0x149/0x1b0 [] down_write+0x3f/0x70 [] ? mm_take_all_locks+0x149/0x1b0 [] mm_take_all_locks+0x149/0x1b0 [] do_mmu_notifier_register+0x68/0x170 [] mmu_notifier_register+0xe/0x10 [] kvm_create_vm+0x22b/0x330 [kvm] [] kvm_dev_ioctl+0xf8/0x1a0 [kvm] [] do_vfs_ioctl+0x9d/0x350 [] ? sysret_check+0x22/0x5d [] sys_ioctl+0x91/0xb0 [] system_call_fastpath+0x16/0x1b Signed-off-by: Jiri Kosina --- mm/mmap.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index f54b235..35730ee 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2886,7 +2886,7 @@ static void vm_lock_anon_vma(struct mm_struct *mm, struct anon_vma *anon_vma) * The LSB of head.next can't change from under us * because we hold the mm_all_locks_mutex. */ - down_write(&anon_vma->root->rwsem); + down_write_nest_lock(&anon_vma->root->rwsem, &mm->mmap_sem); /* * We can safely modify head.next after taking the * anon_vma->root->rwsem. If some other vma in this mm shares -- Jiri Kosina SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org