Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752307AbaL2BQa (ORCPT ); Sun, 28 Dec 2014 20:16:30 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:33139 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751771AbaL2BMN (ORCPT ); Sun, 28 Dec 2014 20:12:13 -0500 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Al Viro" Date: Mon, 29 Dec 2014 02:11:31 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 14/27] deal with deadlock in d_walk() In-Reply-To: X-SA-Exim-Connect-IP: 46.189.28.191 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.66-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Al Viro commit ca5358ef75fc69fee5322a38a340f5739d997c10 upstream. ... by not hitting rename_retry for reasons other than rename having happened. In other words, do _not_ restart when finding that between unlocking the child and locking the parent the former got into __dentry_kill(). Skip the killed siblings instead... Signed-off-by: Al Viro [bwh: Backported to 3.2: - As we only have try_to_ascend() and not d_walk(), apply this change to all callers of try_to_ascend() - Adjust context to make __dentry_kill() apply to d_kill()] Signed-off-by: Ben Hutchings --- fs/dcache.c | 31 ++++++++++++++++--------------- 1 file changed, 16 insertions(+), 15 deletions(-) --- a/fs/dcache.c +++ b/fs/dcache.c @@ -306,9 +306,9 @@ static struct dentry *d_kill(struct dent __releases(parent->d_lock) __releases(dentry->d_inode->i_lock) { - list_del(&dentry->d_child); + __list_del_entry(&dentry->d_child); /* - * Inform try_to_ascend() that we are no longer attached to the + * Inform ascending readers that we are no longer attached to the * dentry tree */ dentry->d_flags |= DCACHE_DENTRY_KILLED; @@ -949,34 +949,6 @@ void shrink_dcache_for_umount(struct sup } } -/* - * This tries to ascend one level of parenthood, but - * we can race with renaming, so we need to re-check - * the parenthood after dropping the lock and check - * that the sequence number still matches. - */ -static struct dentry *try_to_ascend(struct dentry *old, int locked, unsigned seq) -{ - struct dentry *new = old->d_parent; - - rcu_read_lock(); - spin_unlock(&old->d_lock); - spin_lock(&new->d_lock); - - /* - * might go back up the wrong parent if we have had a rename - * or deletion - */ - if (new != old->d_parent || - (old->d_flags & DCACHE_DENTRY_KILLED) || - (!locked && read_seqretry(&rename_lock, seq))) { - spin_unlock(&new->d_lock); - new = NULL; - } - rcu_read_unlock(); - return new; -} - /* * Search for at least 1 mount point in the dentry's subdirs. @@ -1032,17 +1004,32 @@ resume: /* * All done at this level ... ascend and resume the search. */ + rcu_read_lock(); +ascend: if (this_parent != parent) { struct dentry *child = this_parent; - this_parent = try_to_ascend(this_parent, locked, seq); - if (!this_parent) + this_parent = child->d_parent; + + spin_unlock(&child->d_lock); + spin_lock(&this_parent->d_lock); + + /* might go back up the wrong parent if we have had a rename */ + if (!locked && read_seqretry(&rename_lock, seq)) goto rename_retry; next = child->d_child.next; + while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED)) { + if (next == &this_parent->d_subdirs) + goto ascend; + child = list_entry(next, struct dentry, d_child); + next = next->next; + } + rcu_read_unlock(); goto resume; } - spin_unlock(&this_parent->d_lock); if (!locked && read_seqretry(&rename_lock, seq)) goto rename_retry; + spin_unlock(&this_parent->d_lock); + rcu_read_unlock(); if (locked) write_sequnlock(&rename_lock); return 0; /* No mount points found in tree */ @@ -1054,6 +1041,8 @@ positive: return 1; rename_retry: + spin_unlock(&this_parent->d_lock); + rcu_read_unlock(); if (locked) goto again; locked = 1; @@ -1139,23 +1128,40 @@ resume: /* * All done at this level ... ascend and resume the search. */ + rcu_read_lock(); +ascend: if (this_parent != parent) { struct dentry *child = this_parent; - this_parent = try_to_ascend(this_parent, locked, seq); - if (!this_parent) + this_parent = child->d_parent; + + spin_unlock(&child->d_lock); + spin_lock(&this_parent->d_lock); + + /* might go back up the wrong parent if we have had a rename */ + if (!locked && read_seqretry(&rename_lock, seq)) goto rename_retry; next = child->d_child.next; + while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED)) { + if (next == &this_parent->d_subdirs) + goto ascend; + child = list_entry(next, struct dentry, d_child); + next = next->next; + } + rcu_read_unlock(); goto resume; } out: - spin_unlock(&this_parent->d_lock); if (!locked && read_seqretry(&rename_lock, seq)) goto rename_retry; + spin_unlock(&this_parent->d_lock); + rcu_read_unlock(); if (locked) write_sequnlock(&rename_lock); return found; rename_retry: + spin_unlock(&this_parent->d_lock); + rcu_read_unlock(); if (found) return found; if (locked) @@ -2914,26 +2920,43 @@ resume: } spin_unlock(&dentry->d_lock); } + rcu_read_lock(); +ascend: if (this_parent != root) { struct dentry *child = this_parent; if (!(this_parent->d_flags & DCACHE_GENOCIDE)) { this_parent->d_flags |= DCACHE_GENOCIDE; this_parent->d_count--; } - this_parent = try_to_ascend(this_parent, locked, seq); - if (!this_parent) + this_parent = child->d_parent; + + spin_unlock(&child->d_lock); + spin_lock(&this_parent->d_lock); + + /* might go back up the wrong parent if we have had a rename */ + if (!locked && read_seqretry(&rename_lock, seq)) goto rename_retry; next = child->d_child.next; + while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED)) { + if (next == &this_parent->d_subdirs) + goto ascend; + child = list_entry(next, struct dentry, d_child); + next = next->next; + } + rcu_read_unlock(); goto resume; } - spin_unlock(&this_parent->d_lock); if (!locked && read_seqretry(&rename_lock, seq)) goto rename_retry; + spin_unlock(&this_parent->d_lock); + rcu_read_unlock(); if (locked) write_sequnlock(&rename_lock); return; rename_retry: + spin_unlock(&this_parent->d_lock); + rcu_read_unlock(); if (locked) goto again; locked = 1; -- 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/