Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755554Ab3HFObX (ORCPT ); Tue, 6 Aug 2013 10:31:23 -0400 Received: from mail-bk0-f46.google.com ([209.85.214.46]:54212 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753106Ab3HFOaW (ORCPT ); Tue, 6 Aug 2013 10:30:22 -0400 From: Miklos Szeredi To: rwheeler@redhat.com, avati@redhat.com, viro@ZenIV.linux.org.uk Cc: bfoster@redhat.com, dhowells@redhat.com, eparis@redhat.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org, Trond.Myklebust@netapp.com, swhiteho@redhat.com, mszeredi@suse.cz Subject: [PATCH 1/4] vfs: check submounts and drop atomically Date: Tue, 6 Aug 2013 16:30:00 +0200 Message-Id: <1375799403-28544-2-git-send-email-miklos@szeredi.hu> X-Mailer: git-send-email 1.8.1.4 In-Reply-To: <1375799403-28544-1-git-send-email-miklos@szeredi.hu> References: <1375799403-28544-1-git-send-email-miklos@szeredi.hu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7258 Lines: 275 From: Miklos Szeredi We check submounts before doing d_drop() on a non-empty directory dentry in NFS (have_submounts()), but we do not exclude a racing mount. Process A: have_submounts() -> returns false Process B: mount() -> success Process A: d_drop() This patch prepares the ground for the fix by doing the following operations all under the same rename lock: have_submounts() shrink_dcache_parent() d_drop() This is actually an optimization since have_submounts() and shrink_dcache_parent() both traverse the same dentry tree separately. Signed-off-by: Miklos Szeredi --- fs/afs/dir.c | 6 +-- fs/dcache.c | 131 +++++++++++++++++++++++++++++++++++++++++++++++++ fs/gfs2/dentry.c | 6 +-- fs/nfs/dir.c | 10 ++-- fs/sysfs/dir.c | 6 +-- include/linux/dcache.h | 1 + 6 files changed, 146 insertions(+), 14 deletions(-) diff --git a/fs/afs/dir.c b/fs/afs/dir.c index 34494fb..968f50d 100644 --- a/fs/afs/dir.c +++ b/fs/afs/dir.c @@ -687,14 +687,14 @@ not_found: out_bad: if (dentry->d_inode) { /* don't unhash if we have submounts */ - if (have_submounts(dentry)) + if (check_submounts_and_drop(dentry) != 0) goto out_skip; + } else { + d_drop(dentry); } _debug("dropping dentry %s/%s", parent->d_name.name, dentry->d_name.name); - shrink_dcache_parent(dentry); - d_drop(dentry); dput(parent); key_put(key); diff --git a/fs/dcache.c b/fs/dcache.c index 87bdb53..ba429d9 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1224,6 +1224,137 @@ void shrink_dcache_parent(struct dentry * parent) } EXPORT_SYMBOL(shrink_dcache_parent); +static int __check_submounts_and_drop(struct dentry *parent, + struct list_head *dispose) +{ + struct dentry *this_parent; + struct list_head *next; + unsigned seq; + int found = 0; + int locked = 0; + + seq = read_seqbegin(&rename_lock); +again: + this_parent = parent; + spin_lock(&this_parent->d_lock); +repeat: + next = this_parent->d_subdirs.next; +resume: + while (next != &this_parent->d_subdirs) { + struct list_head *tmp = next; + struct dentry *dentry; + + dentry = list_entry(tmp, struct dentry, d_u.d_child); + next = tmp->next; + + spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED); + if (d_mountpoint(dentry)) { + spin_unlock(&dentry->d_lock); + found = -EBUSY; + goto out; + } + + /* + * move only zero ref count dentries to the dispose list. + * + * Those which are presently on the shrink list, being processed + * by shrink_dentry_list(), shouldn't be moved. Otherwise the + * loop in shrink_dcache_parent() might not make any progress + * and loop forever. + */ + if (dentry->d_count) { + dentry_lru_del(dentry); + } else if (!(dentry->d_flags & DCACHE_SHRINK_LIST)) { + dentry_lru_move_list(dentry, dispose); + dentry->d_flags |= DCACHE_SHRINK_LIST; + found++; + } + /* + * We can return to the caller if we have found some (this + * ensures forward progress). We'll be coming back to find + * the rest. + */ + if (found && need_resched()) { + spin_unlock(&dentry->d_lock); + goto out; + } + + /* + * Descend a level if the d_subdirs list is non-empty. + */ + if (!list_empty(&dentry->d_subdirs)) { + spin_unlock(&this_parent->d_lock); + spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_); + this_parent = dentry; + spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_); + goto repeat; + } + + spin_unlock(&dentry->d_lock); + } + /* + * All done at this level ... ascend and resume the search. + */ + if (this_parent != parent) { + struct dentry *child = this_parent; + this_parent = try_to_ascend(this_parent, locked, seq); + if (!this_parent) + goto rename_retry; + next = child->d_u.d_child.next; + goto resume; + } +out: + if (!locked && read_seqretry(&rename_lock, seq)) { + spin_unlock(&this_parent->d_lock); + goto rename_retry; + } + __d_drop(this_parent); + spin_unlock(&this_parent->d_lock); + + if (locked) + write_sequnlock(&rename_lock); + return found; + + +rename_retry: + if (found) + return found; + if (locked) + goto again; + locked = 1; + write_seqlock(&rename_lock); + goto again; +} + +/** + * check_submounts_and_drop - prune dcache, check for submounts and drop + * + * All done as a single atomic operation relative to has_unlinked_ancestor(). + * Returns 0 if successfully unhashed @parent. If there were submounts then + * return -EBUSY. + * + * @dentry: dentry to prune and drop + */ +int check_submounts_and_drop(struct dentry *dentry) +{ + int found; + + for (;;) { + LIST_HEAD(dispose); + found = __check_submounts_and_drop(dentry, &dispose); + if (!list_empty(&dispose)) + shrink_dentry_list(&dispose); + + if (found <= 0) + break; + + cond_resched(); + } + + return found; +} +EXPORT_SYMBOL(check_submounts_and_drop); + /** * __d_alloc - allocate a dcache entry * @sb: filesystem it will belong to diff --git a/fs/gfs2/dentry.c b/fs/gfs2/dentry.c index f2448ab..6964725 100644 --- a/fs/gfs2/dentry.c +++ b/fs/gfs2/dentry.c @@ -94,11 +94,11 @@ invalid_gunlock: gfs2_glock_dq_uninit(&d_gh); invalid: if (inode && S_ISDIR(inode->i_mode)) { - if (have_submounts(dentry)) + if (check_submounts_and_drop(dentry) != 0) goto valid; - shrink_dcache_parent(dentry); + } else { + d_drop(dentry); } - d_drop(dentry); dput(parent); return 0; diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c index e474ca2b..a2fd681 100644 --- a/fs/nfs/dir.c +++ b/fs/nfs/dir.c @@ -1135,14 +1135,14 @@ out_zap_parent: if (inode && S_ISDIR(inode->i_mode)) { /* Purge readdir caches. */ nfs_zap_caches(inode); - /* If we have submounts, don't unhash ! */ - if (have_submounts(dentry)) - goto out_valid; if (dentry->d_flags & DCACHE_DISCONNECTED) goto out_valid; - shrink_dcache_parent(dentry); + /* If we have submounts, don't unhash ! */ + if (check_submounts_and_drop(dentry) != 0) + goto out_valid; + } else { + d_drop(dentry); } - d_drop(dentry); dput(parent); dfprintk(LOOKUPCACHE, "NFS: %s(%s/%s) is invalid\n", __func__, dentry->d_parent->d_name.name, diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c index e068e74..1778320 100644 --- a/fs/sysfs/dir.c +++ b/fs/sysfs/dir.c @@ -348,11 +348,11 @@ out_bad: * to lie about the state of the filesystem to prevent * leaks and other nasty things. */ - if (have_submounts(dentry)) + if (check_submounts_and_drop(dentry) != 0) goto out_valid; - shrink_dcache_parent(dentry); + } else { + d_drop(dentry); } - d_drop(dentry); return 0; } diff --git a/include/linux/dcache.h b/include/linux/dcache.h index b90337c..41b21ca 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -251,6 +251,7 @@ extern void d_prune_aliases(struct inode *); /* test whether we have any submounts in a subdir tree */ extern int have_submounts(struct dentry *); +extern int check_submounts_and_drop(struct dentry *); /* * This adds the entry to the hash queues. -- 1.8.1.4 -- 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/