From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:42328 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932716AbeB1TIX (ORCPT ); Wed, 28 Feb 2018 14:08:23 -0500 Date: Wed, 28 Feb 2018 19:08:21 +0000 From: "Luis R. Rodriguez" Subject: Re: [PATCH] xfs: Correctly invert xfs_buftarg LRU isolation logic Message-ID: <20180228190821.GA14201@wotan.suse.de> References: <20180228154951.31714-1-vbendel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180228154951.31714-1-vbendel@redhat.com> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Vratislav Bendel Cc: linux-xfs@vger.kernel.org, "Darrick J . Wong" , Brian Foster , linux-kernel@vger.kernel.org On Wed, Feb 28, 2018 at 04:49:51PM +0100, Vratislav Bendel wrote: > The function xfs_buftarg_isolate() used by xfs buffer schrinkers > to determine whether a buffer should be isolated and disposed > from LRU list, has inverted logic. > > Excerpt from xfs_buftarg_isolate(): > /* > * Decrement the b_lru_ref count unless the value is already > * zero. If the value is already zero, we need to reclaim the > * buffer, otherwise it gets another trip through the LRU. > */ > if (!atomic_add_unless(&bp->b_lru_ref, -1, 0)) { > spin_unlock(&bp->b_lock); > return LRU_ROTATE; > } > > However, as per documentation, atomic_add_unless() returns _zero_ > if the atomic value was originally equal to the specified *unsless* value. > > Ultimately causing a xfs_buffer with ->b_lru_ref == 0, to take another > trip around LRU, while isolating buffers with non-zero b_lru_ref. > > Signed-off-by: Vratislav Bendel > CC: Brian Foster Can you add a respective Fixes: tag? Also what effects are observed by the user when this happens on the kernel log? Luis