From patchwork Tue Aug 14 03:56:52 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: NeilBrown X-Patchwork-Id: 10565011 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id B96DD1815 for ; Tue, 14 Aug 2018 03:58:33 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id A8F4E29656 for ; Tue, 14 Aug 2018 03:58:33 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 9AA6B29662; Tue, 14 Aug 2018 03:58:33 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 563422965D for ; Tue, 14 Aug 2018 03:58:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731399AbeHNGnl (ORCPT ); Tue, 14 Aug 2018 02:43:41 -0400 Received: from mx2.suse.de ([195.135.220.15]:45090 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725846AbeHNGnk (ORCPT ); Tue, 14 Aug 2018 02:43:40 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 2CB34AF49; Tue, 14 Aug 2018 03:58:23 +0000 (UTC) From: NeilBrown To: Jeff Layton , Alexander Viro Date: Tue, 14 Aug 2018 13:56:52 +1000 Subject: [PATCH 3/5] fs/locks: allow a lock request to block other requests. Cc: "J. Bruce Fields" , Martin Wilck , linux-fsdevel@vger.kernel.org, Frank Filz , linux-kernel@vger.kernel.org Message-ID: <153421901205.24426.3008401633617707303.stgit@noble> In-Reply-To: <153421852728.24426.2111161640156686201.stgit@noble> References: <153421852728.24426.2111161640156686201.stgit@noble> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Currently, a lock can block pending requests, but all pending requests are equal. If lots of pending requests are mutually exclusive, this means they will all be woken up and all but one will fail. This can hurt performance. So we will allow pending requests to block other requests. Only the first request will be woken, and it will wake the others. This patch doesn't implement this fully, but prepares the way. - It acknowledges that a request might be blocking other requests, and when the request is converted to a lock, those blocked requests are moved across. - When a request is requeued or discarded, all blocked requests are woken. - When deadlock-detection looks for the lock which blocks a given request, we follow the chain of ->fl_blocker all the way to the top. Signed-off-by: NeilBrown --- fs/locks.c | 43 +++++++++++++++++++++++++++++++++++-------- 1 file changed, 35 insertions(+), 8 deletions(-) diff --git a/fs/locks.c b/fs/locks.c index de0b9276f23d..9439eebd4eb9 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -408,9 +408,19 @@ void locks_copy_lock(struct file_lock *new, struct file_lock *fl) fl->fl_ops->fl_copy_lock(new, fl); } } - EXPORT_SYMBOL(locks_copy_lock); +static void locks_move_blocks(struct file_lock *new, struct file_lock *fl) +{ + struct file_lock *f; + + spin_lock(&blocked_lock_lock); + list_splice_init(&fl->fl_blocked, &new->fl_blocked); + list_for_each_entry(f, &fl->fl_blocked, fl_block) + f->fl_blocker = new; + spin_unlock(&blocked_lock_lock); +} + static inline int flock_translate_cmd(int cmd) { if (cmd & LOCK_MAND) return cmd & (LOCK_MAND | LOCK_RW); @@ -683,11 +693,15 @@ static void __locks_delete_block(struct file_lock *waiter) static void __locks_wake_up_blocks(struct file_lock *blocker) { + /* Wake up all requests in blocker->fl_blocked, including + * requests blocked by those requests. + */ while (!list_empty(&blocker->fl_blocked)) { struct file_lock *waiter; waiter = list_first_entry(&blocker->fl_blocked, struct file_lock, fl_block); + list_splice_init(&waiter->fl_blocked, &blocker->fl_blocked); __locks_delete_block(waiter); if (waiter->fl_lmops && waiter->fl_lmops->lm_notify) waiter->fl_lmops->lm_notify(waiter); @@ -699,6 +713,7 @@ static void __locks_wake_up_blocks(struct file_lock *blocker) static void locks_delete_block(struct file_lock *waiter) { spin_lock(&blocked_lock_lock); + __locks_wake_up_blocks(waiter); __locks_delete_block(waiter); spin_unlock(&blocked_lock_lock); } @@ -714,13 +729,19 @@ static void locks_delete_block(struct file_lock *waiter) * blocked_lock_lock in some cases when we see that the fl_blocked list is empty. */ static void __locks_insert_block(struct file_lock *blocker, - struct file_lock *waiter) + struct file_lock *waiter) { BUG_ON(!list_empty(&waiter->fl_block)); waiter->fl_blocker = blocker; list_add_tail(&waiter->fl_block, &blocker->fl_blocked); if (IS_POSIX(blocker) && !IS_OFDLCK(blocker)) locks_insert_global_blocked(waiter); + + /* The requests in waiter->fl_blocked are known to conflict with + * waiter, but might not conflict with blocker, or the requests + * and lock which block it. So they all need to be woken. + */ + __locks_wake_up_blocks(waiter); } /* Must be called with flc_lock held. */ @@ -893,8 +914,11 @@ static struct file_lock *what_owner_is_waiting_for(struct file_lock *block_fl) struct file_lock *fl; hash_for_each_possible(blocked_hash, fl, fl_link, posix_owner_key(block_fl)) { - if (posix_same_owner(fl, block_fl)) - return fl->fl_blocker; + if (posix_same_owner(fl, block_fl)) { + while (fl->fl_blocker) + fl = fl->fl_blocker; + return fl; + } } return NULL; } @@ -987,6 +1011,7 @@ static int flock_lock_inode(struct inode *inode, struct file_lock *request) if (request->fl_flags & FL_ACCESS) goto out; locks_copy_lock(new_fl, request); + locks_move_blocks(new_fl, request); locks_insert_lock_ctx(new_fl, &ctx->flc_flock); new_fl = NULL; error = 0; @@ -1179,6 +1204,7 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request, goto out; } locks_copy_lock(new_fl, request); + locks_move_blocks(new_fl, request); locks_insert_lock_ctx(new_fl, &fl->fl_list); fl = new_fl; new_fl = NULL; @@ -2587,13 +2613,14 @@ void locks_remove_file(struct file *filp) int posix_unblock_lock(struct file_lock *waiter) { - int status = 0; + int status = -ENOENT; spin_lock(&blocked_lock_lock); - if (waiter->fl_blocker) + if (waiter->fl_blocker) { + __locks_wake_up_blocks(waiter); __locks_delete_block(waiter); - else - status = -ENOENT; + status = 0; + } spin_unlock(&blocked_lock_lock); return status; }