From patchwork Wed Jan 31 16:10:06 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Wysochanski X-Patchwork-Id: 13539598 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8145612A169 for ; Wed, 31 Jan 2024 16:10:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706717416; cv=none; b=IUj6onOq+9mhjxi4pMZEBfmdB8PFzCWNIcL39mS0S/5c+hPZmRBkqyW0AS8nWPFrTEj01hk2Ux/UUdqddW9p+PL7PhTQ2EtnTzkNW8M3TkXbXejgpj/NxmoNQl5SL8wDvj8OaTHz5QC648yyMw4W3zmUThcNMzP23rQAfH9QR5E= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706717416; c=relaxed/simple; bh=KIwu6QR8r5b8azkpBjVzwHeOJhLwEzV3M5sqyYZeugI=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=l2qHENpgek6XHaOcczOxXVd8eULlZ3IdDEu3tcnPsDMYpxxx2OiWsAyC5JVIXX7EOnhfn4JqlPmuORgGD4NW2uYOjrhPcIEVB3IyXZH/kJuosvXqU01Qaa/649/B9bQdXrwFwKHynRy2eWZryHdW3Sn6VeuISyCcQdgGMKTdcEk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=PQZjHeFG; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="PQZjHeFG" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1706717413; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=Lt3sHrhpNk4V3mKbYLYm+tjlUNv9hVfDfiEkd/fQy0w=; b=PQZjHeFGLLuL/5MFj18ON1pKZpM5i47F1vD2QXw+mI0wDz6aKkz5SAIIPSuRYzJuoE7GZy F5bhg9e4r2KqC4nUGtStG7Ygj08o2JQdC4OxmDVdE8fTuSl0NPn1mrIvjNNd7BAibszaiq Fwr663B9Lik8n5s0aF6aHXfYmX30x/k= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-519-R1GsC0IPMiuIwTcM94QHZg-1; Wed, 31 Jan 2024 11:10:08 -0500 X-MC-Unique: R1GsC0IPMiuIwTcM94QHZg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 35E733C29A71; Wed, 31 Jan 2024 16:10:08 +0000 (UTC) Received: from dwysocha.rdu.csb (unknown [10.22.9.52]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BD6A63C2E; Wed, 31 Jan 2024 16:10:07 +0000 (UTC) From: Dave Wysochanski To: Anna Schumaker , Trond Myklebust Cc: David Howells , Jeff Layton , linux-nfs@vger.kernel.org, linux-cachefs@redhat.com Subject: [PATCH v2] NFS: Fix nfs_netfs_issue_read() xarray locking for writeback interrupt Date: Wed, 31 Jan 2024 11:10:06 -0500 Message-Id: <20240131161006.1475094-1-dwysocha@redhat.com> Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.1 The loop inside nfs_netfs_issue_read() currently does not disable interrupts while iterating through pages in the xarray to submit for NFS read. This is not safe though since after taking xa_lock, another page in the mapping could be processed for writeback inside an interrupt, and deadlock can occur. The fix is simple and clean if we use xa_for_each_range(), which handles the iteration with RCU while reducing code complexity. The problem is easily reproduced with the following test: mount -o vers=3,fsc 127.0.0.1:/export /mnt/nfs dd if=/dev/zero of=/mnt/nfs/file1.bin bs=4096 count=1 echo 3 > /proc/sys/vm/drop_caches dd if=/mnt/nfs/file1.bin of=/dev/null umount /mnt/nfs On the console with a lockdep-enabled kernel a message similar to the following will be seen: ================================ WARNING: inconsistent lock state 6.7.0-lockdbg+ #10 Not tainted -------------------------------- inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage. test5/1708 [HC0[0]:SC0[0]:HE1:SE1] takes: ffff888127baa598 (&xa->xa_lock#4){+.?.}-{3:3}, at: nfs_netfs_issue_read+0x1b2/0x4b0 [nfs] {IN-SOFTIRQ-W} state was registered at: lock_acquire+0x144/0x380 _raw_spin_lock_irqsave+0x4e/0xa0 __folio_end_writeback+0x17e/0x5c0 folio_end_writeback+0x93/0x1b0 iomap_finish_ioend+0xeb/0x6a0 blk_update_request+0x204/0x7f0 blk_mq_end_request+0x30/0x1c0 blk_complete_reqs+0x7e/0xa0 __do_softirq+0x113/0x544 __irq_exit_rcu+0xfe/0x120 irq_exit_rcu+0xe/0x20 sysvec_call_function_single+0x6f/0x90 asm_sysvec_call_function_single+0x1a/0x20 pv_native_safe_halt+0xf/0x20 default_idle+0x9/0x20 default_idle_call+0x67/0xa0 do_idle+0x2b5/0x300 cpu_startup_entry+0x34/0x40 start_secondary+0x19d/0x1c0 secondary_startup_64_no_verify+0x18f/0x19b irq event stamp: 176891 hardirqs last enabled at (176891): [] _raw_spin_unlock_irqrestore+0x44/0x60 hardirqs last disabled at (176890): [] _raw_spin_lock_irqsave+0x79/0xa0 softirqs last enabled at (176646): [] __irq_exit_rcu+0xfe/0x120 softirqs last disabled at (176633): [] __irq_exit_rcu+0xfe/0x120 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(&xa->xa_lock#4); lock(&xa->xa_lock#4); *** DEADLOCK *** 2 locks held by test5/1708: #0: ffff888127baa498 (&sb->s_type->i_mutex_key#22){++++}-{4:4}, at: nfs_start_io_read+0x28/0x90 [nfs] #1: ffff888127baa650 (mapping.invalidate_lock#3){.+.+}-{4:4}, at: page_cache_ra_unbounded+0xa4/0x280 stack backtrace: CPU: 6 PID: 1708 Comm: test5 Kdump: loaded Not tainted 6.7.0-lockdbg+ Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-1.fc39 04/01/2014 Call Trace: dump_stack_lvl+0x5b/0x90 mark_lock+0xb3f/0xd20 __lock_acquire+0x77b/0x3360 _raw_spin_lock+0x34/0x80 nfs_netfs_issue_read+0x1b2/0x4b0 [nfs] netfs_begin_read+0x77f/0x980 [netfs] nfs_netfs_readahead+0x45/0x60 [nfs] nfs_readahead+0x323/0x5a0 [nfs] read_pages+0xf3/0x5c0 page_cache_ra_unbounded+0x1c8/0x280 filemap_get_pages+0x38c/0xae0 filemap_read+0x206/0x5e0 nfs_file_read+0xb7/0x140 [nfs] vfs_read+0x2a9/0x460 ksys_read+0xb7/0x140 Fixes: 000dbe0bec05 ("NFS: Convert buffered read paths to use netfs when fscache is enabled") Suggested-by: Jeff Layton Signed-off-by: Dave Wysochanski Reviewed-by: Jeff Layton Reviewed-by: David Howells --- fs/nfs/fscache.c | 9 ++------- 1 file changed, 2 insertions(+), 7 deletions(-) diff --git a/fs/nfs/fscache.c b/fs/nfs/fscache.c index b05717fe0d4e..60a3c28784e0 100644 --- a/fs/nfs/fscache.c +++ b/fs/nfs/fscache.c @@ -307,11 +307,11 @@ static void nfs_netfs_issue_read(struct netfs_io_subrequest *sreq) struct inode *inode = sreq->rreq->inode; struct nfs_open_context *ctx = sreq->rreq->netfs_priv; struct page *page; + unsigned long idx; int err; pgoff_t start = (sreq->start + sreq->transferred) >> PAGE_SHIFT; pgoff_t last = ((sreq->start + sreq->len - sreq->transferred - 1) >> PAGE_SHIFT); - XA_STATE(xas, &sreq->rreq->mapping->i_pages, start); nfs_pageio_init_read(&pgio, inode, false, &nfs_async_read_completion_ops); @@ -322,19 +322,14 @@ static void nfs_netfs_issue_read(struct netfs_io_subrequest *sreq) pgio.pg_netfs = netfs; /* used in completion */ - xas_lock(&xas); - xas_for_each(&xas, page, last) { + xa_for_each_range(&sreq->rreq->mapping->i_pages, idx, page, start, last) { /* nfs_read_add_folio() may schedule() due to pNFS layout and other RPCs */ - xas_pause(&xas); - xas_unlock(&xas); err = nfs_read_add_folio(&pgio, ctx, page_folio(page)); if (err < 0) { netfs->error = err; goto out; } - xas_lock(&xas); } - xas_unlock(&xas); out: nfs_pageio_complete_read(&pgio); nfs_netfs_put(netfs);