From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex Elder Subject: Re: [PATCH 1/2] bdi: mark the bdi flusher busy when being forked Date: Wed, 13 Apr 2011 14:29:23 -0500 Message-ID: <1302722963.2023.66.camel@doink> References: <1302157196-1988-1-git-send-email-david@fromorbit.com> <1302157196-1988-2-git-send-email-david@fromorbit.com> Reply-To: aelder@sgi.com Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: xfs@oss.sgi.com, linux-fsdevel@vger.kernel.org To: Dave Chinner Return-path: Received: from relay2.sgi.com ([192.48.179.30]:40712 "HELO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with SMTP id S1758066Ab1DMTaC (ORCPT ); Wed, 13 Apr 2011 15:30:02 -0400 In-Reply-To: <1302157196-1988-2-git-send-email-david@fromorbit.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Thu, 2011-04-07 at 16:19 +1000, Dave Chinner wrote: > From: Dave Chinner > > Recetn attempts to use writeback_inode_sb_nr_if_idle() in XFs from > memory reclaim context have caused deadlocks because memory reclaim > call be called from a failed allocation during forking a flusher > thread. The shrinker then attempts to trigger writeback and the bdi > is considered idle because writeback is not in progress yet and then > deadlocks because bdi_queue_work() blocks waiting for the > BDI_Pending bit to clear which will never happen because it needs > the fork to complete. > > To avoid this deadlock, consider writeback to be in progress if the > flusher thread is being created. This prevents reclaim from blocking > waiting for it be forked and hence avoids the deadlock. I don't believe it matters, but BDI_pending is also set while a writeback flusher thread is being shut down. In any case, a handy use of that flag bit. Reviewed-by: Alex Elder > Signed-off-by: Dave Chinner