From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CE4CFC433E2 for ; Mon, 14 Sep 2020 14:08:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7E3AA2074B for ; Mon, 14 Sep 2020 14:08:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="AWvk9o8h" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726790AbgINOIU (ORCPT ); Mon, 14 Sep 2020 10:08:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34422 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726402AbgINOHh (ORCPT ); Mon, 14 Sep 2020 10:07:37 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0C008C06174A for ; Mon, 14 Sep 2020 07:07:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=LcdoEWDjr+1vruLTp3pTqHW/nKPn+9jvg4METqBqsKc=; b=AWvk9o8hEfhwm/nYAfgLut2hu6 N/ABDGWAA1v3pKbgAqWUmHrQzGvBIuvEg6u1r8k/UidGlEv1vw1hvXf0S+4y1xNbtNEHlPBqcwbW/ Qh76c1QxCrXNhWeBA2O/rtrCuyAd0fuVK1pQT8M0Fj9OHhvSZCXkxGahvBCR7o1g1ymHILXXKbT3d X8ZBQXZtx+/QPH0psg8UTqprFLVUd3gP/mKqjG3yJ36c9UirP+yRXvln6XRShd5tXGnCDvOnLh3+l rzNdp7bYrHRuTD0j+isD7W94lt6bo29u/SrexppuND9rlG+iVJo2B/yqMY2eIYV+srcYKCOJhCwvv CNeRfExA==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kHp8n-00074z-AC; Mon, 14 Sep 2020 14:07:34 +0000 Date: Mon, 14 Sep 2020 15:07:33 +0100 From: Matthew Wilcox To: Pradeep P V K Cc: miklos@szeredi.hu, linux-fsdevel@vger.kernel.org, stummala@codeaurora.org, sayalil@codeaurora.org Subject: Re: [PATCH V1] fuse: Remove __GFP_FS flag to avoid allocator recursing Message-ID: <20200914140733.GP6583@casper.infradead.org> References: <1600091775-10639-1-git-send-email-ppvk@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1600091775-10639-1-git-send-email-ppvk@codeaurora.org> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon, Sep 14, 2020 at 07:26:15PM +0530, Pradeep P V K wrote: > Process#1(kswapd) held an inode lock and initaited a writeback to free > the pages, as the inode superblock is fuse, process#2 forms a fuse > request. Process#3 (Fuse daemon threads) while serving process#2 request, > it requires memory(pages) and as the system is already running in low > memory it ends up in calling try_to_ free_pages(), which might now call > kswapd again, which is already stuck with an inode lock held. Thus forms > a deadlock. > > So, remove __GFP_FS flag to avoid allocator recursing into the > filesystem that might already held locks. This is the wrong way to fix the problem. The fuse daemon threads should have called memalloc_nofs_save() as this prevents them from inadvertently tripping over other places where they forgot to use GFP_NOFS (or have no way to pass a GFP_NOFS flags argument).