Return-Path: Received: from mx2.suse.de ([195.135.220.15]:41544 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751775AbbG2D7Y (ORCPT ); Tue, 28 Jul 2015 23:59:24 -0400 Date: Wed, 29 Jul 2015 13:59:14 +1000 From: NeilBrown To: Kinglong Mee , Al Viro Cc: "J. Bruce Fields" , "linux-nfs@vger.kernel.org" , linux-fsdevel@vger.kernel.org, Trond Myklebust Subject: [PATCH] fs-pin: allow pin_remove() to be called other than from ->kill() Message-ID: <20150729135914.13cb0f86@noble> In-Reply-To: <55B5A186.7040004@gmail.com> References: <55B5A012.1030006@gmail.com> <55B5A186.7040004@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-nfs-owner@vger.kernel.org List-ID: fs-pin currently assumes when either the vfsmount or the fs_pin wants to unpin, pin_kill() will be called. This requires that the ->kill() function can wait for any transient references to the fs_pin to be released. If the structure containing the fs_pin doesn't already have the ability to wait for references, this can be a burden. As the fs_pin already has infrastructure for waiting, that can be leveraged to remove the burden. In this alternate scenario, only the vfsmount calls pin_kill() when it wants to unpin. The owner of the fs_pin() instead calls pin_remove(). The ->kill() function removes any long-term references, and then calls pin_kill() (recursively). When the last reference on (the structure containing) the fs_pin is dropped, pin_remove() will be called and the (recursive) pin_kill() call will complete. For this to be safe, the final "put" must *not* free the structure if pin_kill() has already been called, as that could leave ->kill() accessing freed data. So we provide a return value for pin_remove() which reports the old ->done value. When final put calls pin_remove() it checks that value. If it was 0, then pin_kill() has not called ->kill and will not, so final put can free the data structure. If it was -1, then pin_kill() has called ->kill, and ->kill will free the data structure - final put must not touch it. This makes the 'wait' infrastructure of fs_pin available to any pinning client which wants to use it. Signed-Off-By: NeilBrown --- Hi Al, do you see this as a workable solution? I think it will improve the nfsd pining patch a lot. Thanks, NeilBrown diff --git a/fs/fs_pin.c b/fs/fs_pin.c index 611b5408f6ec..b7954a9d17da 100644 --- a/fs/fs_pin.c +++ b/fs/fs_pin.c @@ -6,16 +6,32 @@ static DEFINE_SPINLOCK(pin_lock); -void pin_remove(struct fs_pin *pin) +/** + * pin_remove - disconnect an fs_pin from the pinned structure. + * @pin: The struct fs_pin which is pinning something. + * + * Detach a 'pin' which was added by pin_insert(). A return value + * of -1 implies that pin_kill() has already been called and that the + * ->kill() function now owns the data structure containing @pin. + * The function which called pin_remove() must not touch the data structure + * again (unless it is the ->kill() function itself). + * A return value of 0 implies an uneventful disconnect: pin_kill() has not called, + * and will not call, the ->kill() function on this @pin. + * Any other return value is a usage error - e.g. repeated call to pin_remove(). + */ +int pin_remove(struct fs_pin *pin) { + int ret; spin_lock(&pin_lock); hlist_del_init(&pin->m_list); hlist_del_init(&pin->s_list); spin_unlock(&pin_lock); spin_lock_irq(&pin->wait.lock); + ret = pin->done; pin->done = 1; wake_up_locked(&pin->wait); spin_unlock_irq(&pin->wait.lock); + return ret; } void pin_insert_group(struct fs_pin *pin, struct vfsmount *m, struct hlist_head *p) diff --git a/include/linux/fs_pin.h b/include/linux/fs_pin.h index 3886b3bffd7f..2fe9d3ba09e8 100644 --- a/include/linux/fs_pin.h +++ b/include/linux/fs_pin.h @@ -18,7 +18,7 @@ static inline void init_fs_pin(struct fs_pin *p, void (*kill)(struct fs_pin *)) p->kill = kill; } -void pin_remove(struct fs_pin *); +int pin_remove(struct fs_pin *); void pin_insert_group(struct fs_pin *, struct vfsmount *, struct hlist_head *); void pin_insert(struct fs_pin *, struct vfsmount *); void pin_kill(struct fs_pin *);