From patchwork Mon Mar 9 05:58:20 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric Biggers X-Patchwork-Id: 11426067 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 5BB2114BC for ; Mon, 9 Mar 2020 05:59:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3359E20727 for ; Mon, 9 Mar 2020 05:59:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1583733593; bh=S4XLLB0u7ZrovlJVWMX+h/jJbJG8MDh37MbRley/rR4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=IoIDRwV6HqgtZQt6F5y3M6nMdE6+iTiy6kxenJ+c8WxlZr7kuxtcRYGA9S1hHXEVV MQa+0y45hpWdmVquM4RYkuFNFYZZESOTxSnUkGRtolxSD4rdmgRVKbklyDR0jOWNb8 2xK8hlADV22lftZJeRqcWwGfWPmmW2dzNGmMO2JE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726368AbgCIF7w (ORCPT ); Mon, 9 Mar 2020 01:59:52 -0400 Received: from mail.kernel.org ([198.145.29.99]:57372 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725796AbgCIF7w (ORCPT ); Mon, 9 Mar 2020 01:59:52 -0400 Received: from sol.hsd1.ca.comcast.net (c-107-3-166-239.hsd1.ca.comcast.net [107.3.166.239]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EC9DF20727; Mon, 9 Mar 2020 05:59:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1583733592; bh=S4XLLB0u7ZrovlJVWMX+h/jJbJG8MDh37MbRley/rR4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=pmPSswZ2vGgU8If1BI7OFSZ6GWcpwVvgwiBSM+aK21bouP1Ych0a9sf7i1j+FRvAU 5iP1oGe48nvls1HTGErJ6MsWwTemo1jRjq1NIhPSXtC5ClszMwGFXS+M8PTiPOdOYk Fjdaw/PH2e7uQI8lXzLGshTFnTxphXb4m7YjHQwg= From: Eric Biggers To: linux-cifs@vger.kernel.org Cc: linux-ext4@vger.kernel.org, syzkaller-bugs@googlegroups.com, linux-kernel@vger.kernel.org Subject: [PATCH v3] cifs: clear PF_MEMALLOC before exiting demultiplex thread Date: Sun, 8 Mar 2020 22:58:20 -0700 Message-Id: <20200309055820.272703-1-ebiggers@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200309055621.GA272474@sol.localdomain> References: <20200309055621.GA272474@sol.localdomain> MIME-Version: 1.0 Sender: linux-cifs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-cifs@vger.kernel.org From: Eric Biggers Leaving PF_MEMALLOC set when exiting a kthread causes it to remain set during do_exit(). That can confuse things. For example, if BSD process accounting is enabled and the accounting file has FS_SYNC_FL set and is located on an ext4 filesystem without a journal, then do_exit() can end up calling ext4_write_inode(). That triggers the WARN_ON_ONCE(current->flags & PF_MEMALLOC) there, as it assumes (appropriately) that inodes aren't written when allocating memory. This was originally reported for another kernel thread, xfsaild() [1]. cifs_demultiplex_thread() also exits with PF_MEMALLOC set, so it's potentially subject to this same class of issue -- though I haven't been able to reproduce the WARN_ON_ONCE() via CIFS, since unlike xfsaild(), cifs_demultiplex_thread() is sent SIGKILL before exiting, and that interrupts the write to the BSD process accounting file. Either way, leaving PF_MEMALLOC set is potentially problematic. Let's clean this up by properly saving and restoring PF_MEMALLOC. [1] https://lore.kernel.org/r/0000000000000e7156059f751d7b@google.com Signed-off-by: Eric Biggers --- v3: improved commit message v2: added missing include fs/cifs/connect.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c index 4804d1df8c1cf..97b8eb585cf9d 100644 --- a/fs/cifs/connect.c +++ b/fs/cifs/connect.c @@ -21,6 +21,7 @@ #include #include #include +#include #include #include #include @@ -1164,8 +1165,9 @@ cifs_demultiplex_thread(void *p) struct task_struct *task_to_wake = NULL; struct mid_q_entry *mids[MAX_COMPOUND]; char *bufs[MAX_COMPOUND]; + unsigned int noreclaim_flag; - current->flags |= PF_MEMALLOC; + noreclaim_flag = memalloc_noreclaim_save(); cifs_dbg(FYI, "Demultiplex PID: %d\n", task_pid_nr(current)); length = atomic_inc_return(&tcpSesAllocCount); @@ -1320,6 +1322,7 @@ cifs_demultiplex_thread(void *p) set_current_state(TASK_RUNNING); } + memalloc_noreclaim_restore(noreclaim_flag); module_put_and_exit(0); }