From 572043c90db65b45a4efd959db7458edcf6411ad Mon Sep 17 00:00:00 2001 From: Jiri Kosina Date: Fri, 11 Jan 2013 14:31:59 -0800 Subject: [PATCH] mm: mmap: annotate vm_lock_anon_vma locking properly for lockdep Commit 5a505085f043 ("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 lock_acquire+0x121/0x190 down_write+0x3f/0x70 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 sys_ioctl+0x91/0xb0 system_call_fastpath+0x16/0x1b Signed-off-by: Jiri Kosina Cc: Rik van Riel Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Mel Gorman Tested-by: Sedat Dilek Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/mmap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/mmap.c b/mm/mmap.c index f54b235f29a9..35730ee9d515 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