Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756533AbZGNUdX (ORCPT ); Tue, 14 Jul 2009 16:33:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756520AbZGNUdV (ORCPT ); Tue, 14 Jul 2009 16:33:21 -0400 Received: from qmta10.westchester.pa.mail.comcast.net ([76.96.62.17]:49640 "EHLO QMTA10.westchester.pa.mail.comcast.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756470AbZGNUdP (ORCPT ); Tue, 14 Jul 2009 16:33:15 -0400 To: Tyler Hicks , Dustin Kirkland Cc: linux-kernel@vger.kernel.org Subject: [PATCH] ecryptfs: Remove unneeded locking that triggers lockdep false positives X-Message-Flag: Warning: May contain useful information X-Priority: 1 X-MSMail-Priority: High From: Roland Dreier Date: Tue, 14 Jul 2009 13:32:56 -0700 Message-ID: <87skgzdmyv.fsf@shaolin.home.digitalvampire.org> User-Agent: Gnus/5.1008 (Gnus v5.10.8) XEmacs/21.4.21 (linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6794 Lines: 153 In ecryptfs_destroy_inode(), inode_info->lower_file_mutex is locked, and just after the mutex is unlocked, the code does: kmem_cache_free(ecryptfs_inode_info_cache, inode_info); This means that if another context could possibly try to take the same mutex as ecryptfs_destroy_inode(), then it could end up getting the mutex just before the data structure containing the mutex is freed. So any such use would be an obvious use-after-free bug (catchable with slab poisoning or mutex debugging), and therefore the locking in ecryptfs_destroy_inode() is not needed and can be dropped. Similarly, in ecryptfs_destroy_crypt_stat(), crypt_stat->keysig_list_mutex is locked, and then the mutex is unlocked just before the code does: memset(crypt_stat, 0, sizeof(struct ecryptfs_crypt_stat)); Therefore taking this mutex is similarly not necessary. Removing this locking fixes false-positive lockdep reports such as the following (and they are false-positives for exactly the same reason that the locking is not needed): ================================= [ INFO: inconsistent lock state ] 2.6.31-2-generic #14~rbd3 --------------------------------- inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} usage. kswapd0/323 [HC0[0]:SC0[0]:HE1:SE1] takes: (&inode_info->lower_file_mutex){+.+.?.}, at: [] ecryptfs_destroy_inode+0x34/0x100 {RECLAIM_FS-ON-W} state was registered at: [] mark_held_locks+0x6c/0xa0 [] lockdep_trace_alloc+0xaf/0xe0 [] kmem_cache_alloc+0x41/0x1a0 [] get_empty_filp+0x7a/0x1a0 [] dentry_open+0x36/0xc0 [] ecryptfs_privileged_open+0x5c/0x2e0 [] ecryptfs_init_persistent_file+0xa3/0xe0 [] ecryptfs_lookup_and_interpose_lower+0x278/0x380 [] ecryptfs_lookup+0x12a/0x250 [] real_lookup+0xea/0x160 [] do_lookup+0xb8/0xf0 [] __link_path_walk+0x518/0x870 [] path_walk+0x5c/0xc0 [] do_path_lookup+0x5b/0xa0 [] user_path_at+0x57/0xa0 [] vfs_fstatat+0x3c/0x80 [] vfs_stat+0x1b/0x20 [] sys_newstat+0x24/0x50 [] system_call_fastpath+0x16/0x1b [] 0xffffffffffffffff irq event stamp: 7811 hardirqs last enabled at (7811): [] call_rcu+0x5f/0x90 hardirqs last disabled at (7810): [] call_rcu+0x33/0x90 softirqs last enabled at (3764): [] __do_softirq+0x14a/0x220 softirqs last disabled at (3751): [] call_softirq+0x1c/0x30 other info that might help us debug this: 2 locks held by kswapd0/323: #0: (shrinker_rwsem){++++..}, at: [] shrink_slab+0x3d/0x190 #1: (&type->s_umount_key#35){.+.+..}, at: [] prune_dcache+0xd1/0x1b0 stack backtrace: Pid: 323, comm: kswapd0 Tainted: G C 2.6.31-2-generic #14~rbd3 Call Trace: [] print_usage_bug+0x18c/0x1a0 [] ? check_usage_forwards+0x0/0xc0 [] mark_lock_irq+0xf2/0x280 [] mark_lock+0x137/0x1d0 [] ? fsnotify_clear_marks_by_inode+0x30/0xf0 [] mark_irqflags+0xc6/0x1a0 [] __lock_acquire+0x287/0x430 [] lock_acquire+0xa5/0x150 [] ? ecryptfs_destroy_inode+0x34/0x100 [] ? __lock_acquire+0x237/0x430 [] __mutex_lock_common+0x4d/0x3d0 [] ? ecryptfs_destroy_inode+0x34/0x100 [] ? fsnotify_clear_marks_by_inode+0x30/0xf0 [] ? ecryptfs_destroy_inode+0x34/0x100 [] ? _raw_spin_unlock+0x5e/0xb0 [] mutex_lock_nested+0x46/0x60 [] ecryptfs_destroy_inode+0x34/0x100 [] destroy_inode+0x87/0xd0 [] generic_delete_inode+0x12c/0x1a0 [] iput+0x62/0x70 [] dentry_iput+0x98/0x110 [] d_kill+0x50/0x80 [] prune_one_dentry+0xa3/0xc0 [] __shrink_dcache_sb+0x271/0x290 [] prune_dcache+0x109/0x1b0 [] shrink_dcache_memory+0x3f/0x50 [] shrink_slab+0x12d/0x190 [] balance_pgdat+0x4d7/0x640 [] ? finish_task_switch+0x40/0x150 [] ? isolate_pages_global+0x0/0x60 [] kswapd+0x117/0x170 [] ? autoremove_wake_function+0x0/0x40 [] ? kswapd+0x0/0x170 [] kthread+0x9e/0xb0 [] child_rip+0xa/0x20 [] ? restore_args+0x0/0x30 [] ? kthread+0x0/0xb0 [] ? child_rip+0x0/0x20 Signed-off-by: Roland Dreier --- fs/ecryptfs/crypto.c | 2 -- fs/ecryptfs/super.c | 2 -- 2 files changed, 0 insertions(+), 4 deletions(-) diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c index b91851f..4610fd6 100644 --- a/fs/ecryptfs/crypto.c +++ b/fs/ecryptfs/crypto.c @@ -245,13 +245,11 @@ void ecryptfs_destroy_crypt_stat(struct ecryptfs_crypt_stat *crypt_stat) crypto_free_blkcipher(crypt_stat->tfm); if (crypt_stat->hash_tfm) crypto_free_hash(crypt_stat->hash_tfm); - mutex_lock(&crypt_stat->keysig_list_mutex); list_for_each_entry_safe(key_sig, key_sig_tmp, &crypt_stat->keysig_list, crypt_stat_list) { list_del(&key_sig->crypt_stat_list); kmem_cache_free(ecryptfs_key_sig_cache, key_sig); } - mutex_unlock(&crypt_stat->keysig_list_mutex); memset(crypt_stat, 0, sizeof(struct ecryptfs_crypt_stat)); } diff --git a/fs/ecryptfs/super.c b/fs/ecryptfs/super.c index 12d6496..b15a43a 100644 --- a/fs/ecryptfs/super.c +++ b/fs/ecryptfs/super.c @@ -77,7 +77,6 @@ static void ecryptfs_destroy_inode(struct inode *inode) struct ecryptfs_inode_info *inode_info; inode_info = ecryptfs_inode_to_private(inode); - mutex_lock(&inode_info->lower_file_mutex); if (inode_info->lower_file) { struct dentry *lower_dentry = inode_info->lower_file->f_dentry; @@ -89,7 +88,6 @@ static void ecryptfs_destroy_inode(struct inode *inode) d_drop(lower_dentry); } } - mutex_unlock(&inode_info->lower_file_mutex); ecryptfs_destroy_crypt_stat(&inode_info->crypt_stat); kmem_cache_free(ecryptfs_inode_info_cache, inode_info); } -- 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/