From patchwork Thu Apr 27 22:49:43 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Darrick J. Wong" X-Patchwork-Id: 13225804 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0E1B9C77B61 for ; Thu, 27 Apr 2023 22:49:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344327AbjD0Wtq (ORCPT ); Thu, 27 Apr 2023 18:49:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53204 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343716AbjD0Wtp (ORCPT ); Thu, 27 Apr 2023 18:49:45 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8E4B02123 for ; Thu, 27 Apr 2023 15:49:44 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 2DAAA64038 for ; Thu, 27 Apr 2023 22:49:44 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 86F86C433D2; Thu, 27 Apr 2023 22:49:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1682635783; bh=C+404QwoGCrmWIxxo6DINbpm6sBY5bXsU3IvKpS6dVg=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=Y/ptOypDkPAXpEIP2G9Z4RBrL5672BYAiG6E1fJmw7Na7aRfQqh8YI0UyTea+sJBD hQg/uVQiuKcz7phMS7c03I97KeQ6Q7rIoVmT/4oWGbujx9pdFNyV74a8Xeg3/ZLEl+ h6wwRaM8Tl6kNU0pJ7fT2k6OSYh7ObSPXCc3kFaVmQz28VFecveUjDl/kwckanAW9E BoSujyvPanweuOusidKPWNghFsZmU8g8KYu10VEHeF2Mij7OINwJfTC4FkX3qNxy7S iFle33ng7i8bw74AYg6Ars06YSIIuCvJiQt1fDjVKc3bf6rRJcLVwwrobrcjgEmS3q cx+uEJs5rRPqg== Subject: [PATCH 4/4] xfs: fix xfs_inodegc_stop racing with mod_delayed_work From: "Darrick J. Wong" To: david@fromorbit.com, djwong@kernel.org Cc: linux-xfs@vger.kernel.org Date: Thu, 27 Apr 2023 15:49:43 -0700 Message-ID: <168263578315.1719564.9753279529602110442.stgit@frogsfrogsfrogs> In-Reply-To: <168263576040.1719564.2454266085026973056.stgit@frogsfrogsfrogs> References: <168263576040.1719564.2454266085026973056.stgit@frogsfrogsfrogs> User-Agent: StGit/0.19 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org From: Darrick J. Wong syzbot reported this warning from the faux inodegc shrinker that tries to kick off inodegc work: ------------[ cut here ]------------ WARNING: CPU: 1 PID: 102 at kernel/workqueue.c:1445 __queue_work+0xd44/0x1120 kernel/workqueue.c:1444 RIP: 0010:__queue_work+0xd44/0x1120 kernel/workqueue.c:1444 Call Trace: __queue_delayed_work+0x1c8/0x270 kernel/workqueue.c:1672 mod_delayed_work_on+0xe1/0x220 kernel/workqueue.c:1746 xfs_inodegc_shrinker_scan fs/xfs/xfs_icache.c:2212 [inline] xfs_inodegc_shrinker_scan+0x250/0x4f0 fs/xfs/xfs_icache.c:2191 do_shrink_slab+0x428/0xaa0 mm/vmscan.c:853 shrink_slab+0x175/0x660 mm/vmscan.c:1013 shrink_one+0x502/0x810 mm/vmscan.c:5343 shrink_many mm/vmscan.c:5394 [inline] lru_gen_shrink_node mm/vmscan.c:5511 [inline] shrink_node+0x2064/0x35f0 mm/vmscan.c:6459 kswapd_shrink_node mm/vmscan.c:7262 [inline] balance_pgdat+0xa02/0x1ac0 mm/vmscan.c:7452 kswapd+0x677/0xd60 mm/vmscan.c:7712 kthread+0x2e8/0x3a0 kernel/kthread.c:376 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308 This warning corresponds to this code in __queue_work: /* * For a draining wq, only works from the same workqueue are * allowed. The __WQ_DESTROYING helps to spot the issue that * queues a new work item to a wq after destroy_workqueue(wq). */ if (unlikely(wq->flags & (__WQ_DESTROYING | __WQ_DRAINING) && WARN_ON_ONCE(!is_chained_work(wq)))) return; For this to trip, we must have a thread draining the inodedgc workqueue and a second thread trying to queue inodegc work to that workqueue. This can happen if freezing or a ro remount race with reclaim poking our faux inodegc shrinker and another thread dropping an unlinked O_RDONLY file: Thread 0 Thread 1 Thread 2 xfs_inodegc_stop xfs_inodegc_shrinker_scan xfs_is_inodegc_enabled xfs_clear_inodegc_enabled xfs_inodegc_queue_all xfs_inodegc_queue xfs_is_inodegc_enabled drain_workqueue llist_empty mod_delayed_work_on(..., 0) __queue_work In other words, everything between the access to inodegc_enabled state and the decision to poke the inodegc workqueue requires some kind of coordination to avoid the WQ_DRAINING state. We could perhaps introduce a lock here, but we could also try to eliminate WQ_DRAINING from the picture. We could replace the drain_workqueue call with a loop that flushes the workqueue and queues workers as long as there is at least one inode present in the per-cpu inodegc llists. We've disabled inodegc at this point, so we know that the number of queued inodes will eventually hit zero as long as xfs_inodegc_start cannot reactivate the workers. There are four callers of xfs_inodegc_start. Three of them come from the VFS with s_umount held: filesystem thawing, failed filesystem freezing, and the rw remount transition. The fourth caller is mounting rw (no remount or freezing possible). There are three callers ofs xfs_inodegc_stop. One is unmounting (no remount or thaw possible). Two of them come from the VFS with s_umount held: fs freezing and ro remount transition. Hence, it is correct to replace the drain_workqueue call with a loop that drains the inodegc llists. Fixes: 6191cf3ad59f ("xfs: flush inodegc workqueue tasks before cancel") Signed-off-by: Darrick J. Wong --- fs/xfs/xfs_icache.c | 30 +++++++++++++++++++++++++----- 1 file changed, 25 insertions(+), 5 deletions(-) diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c index 4b63c065ef19..14cb660d7f55 100644 --- a/fs/xfs/xfs_icache.c +++ b/fs/xfs/xfs_icache.c @@ -435,18 +435,23 @@ xfs_iget_check_free_state( } /* Make all pending inactivation work start immediately. */ -static void +static bool xfs_inodegc_queue_all( struct xfs_mount *mp) { struct xfs_inodegc *gc; int cpu; + bool ret = false; for_each_online_cpu(cpu) { gc = per_cpu_ptr(mp->m_inodegc, cpu); - if (!llist_empty(&gc->list)) + if (!llist_empty(&gc->list)) { mod_delayed_work_on(cpu, mp->m_inodegc_wq, &gc->work, 0); + ret = true; + } } + + return ret; } /* @@ -1911,24 +1916,39 @@ xfs_inodegc_flush( /* * Flush all the pending work and then disable the inode inactivation background - * workers and wait for them to stop. + * workers and wait for them to stop. Do not call xfs_inodegc_start until this + * finishes. */ void xfs_inodegc_stop( struct xfs_mount *mp) { + bool rerun; + if (!xfs_clear_inodegc_enabled(mp)) return; + /* + * Drain all pending inodegc work, including inodes that could be + * queued by racing xfs_inodegc_queue or xfs_inodegc_shrinker_scan + * threads that sample the inodegc state just prior to us clearing it. + * The inodegc flag state prevents new threads from queuing more + * inodes, so we queue pending work items and flush the workqueue until + * all inodegc lists are empty. + */ xfs_inodegc_queue_all(mp); - drain_workqueue(mp->m_inodegc_wq); + do { + flush_workqueue(mp->m_inodegc_wq); + rerun = xfs_inodegc_queue_all(mp); + } while (rerun); trace_xfs_inodegc_stop(mp, __return_address); } /* * Enable the inode inactivation background workers and schedule deferred inode - * inactivation work if there is any. + * inactivation work if there is any. Do not call this while xfs_inodegc_stop + * is running. */ void xfs_inodegc_start(