From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ipmail07.adl2.internode.on.net ([150.101.137.131]:27871 "EHLO ipmail07.adl2.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751739AbeFGWIx (ORCPT ); Thu, 7 Jun 2018 18:08:53 -0400 Date: Fri, 8 Jun 2018 08:08:50 +1000 From: Dave Chinner Subject: Re: [PATCH 2/2] xfs: xfs_reflink_convert_cow() memory allocation deadlock Message-ID: <20180607220850.GS10363@dastard> References: <20180607052132.6207-1-david@fromorbit.com> <20180607052132.6207-3-david@fromorbit.com> <77a374f5-3d05-5d53-0253-265c801eb2f8@oracle.com> <20180607144631.GC25007@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180607144631.GC25007@magnolia> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: "Darrick J. Wong" Cc: Allison Henderson , linux-xfs@vger.kernel.org On Thu, Jun 07, 2018 at 07:46:31AM -0700, Darrick J. Wong wrote: > On Wed, Jun 06, 2018 at 10:56:50PM -0700, Allison Henderson wrote: > > On 06/06/2018 10:21 PM, Dave Chinner wrote: > > > From: Dave Chinner > > > > > > xfs_reflink_convert_cow() manipulates the incore extent list > > > in GFP_KERNEL context in the IO submission path whilst holding > > > locked pages under writeback. This is a memory reclaim deadlock > > > vector. This code is not in a transaction, so any memory allocations > > > it makes aren't protected via the memalloc_nofs_save() context that > > > transactions carry. > > > > > > Hence we need to run this call under memalloc_nofs_save() context to > > > prevent potential memory allocations from being run as GFP_KERNEL > > > and deadlocking. > > > > > > Signed-Off-By: Dave Chinner > > > --- > > > fs/xfs/xfs_aops.c | 11 +++++++++++ > > > fs/xfs/xfs_buf.c | 1 - > > > fs/xfs/xfs_linux.h | 1 + > > > 3 files changed, 12 insertions(+), 1 deletion(-) > > > > > > diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c > > > index 767d53222f31..1eb625fdcb1e 100644 > > > --- a/fs/xfs/xfs_aops.c > > > +++ b/fs/xfs/xfs_aops.c > > > @@ -531,8 +531,19 @@ xfs_submit_ioend( > > > { > > > /* Convert CoW extents to regular */ > > > if (!status && ioend->io_type == XFS_IO_COW) { > > > + /* > > > + * Yuk. This can do memory allocation, but is not a > > > + * transactional operation so everything is done in GFP_KERNEL > > > + * context. That can deadlock, because we hold pages in > > > + * writeback state and GFP_KERNEL allocations can block on them. > > > + * Hence we must operate in nofs conditions here. > > > + */ > > > + unsigned nofs_flag; > > > + > > > + nofs_flag = memalloc_nofs_save(); > > > status = xfs_reflink_convert_cow(XFS_I(ioend->io_inode), > > > ioend->io_offset, ioend->io_size); > > > + memalloc_nofs_restore(nofs_flag); > > DOH. :) > > > > } > > > /* Reserve log space if we might write beyond the on-disk inode size. */ > > > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c > > > index 980bc48979e9..e9c058e3761c 100644 > > > --- a/fs/xfs/xfs_buf.c > > > +++ b/fs/xfs/xfs_buf.c > > > @@ -21,7 +21,6 @@ > > > #include > > > #include > > > #include > > > -#include > > > #include "xfs_format.h" > > > #include "xfs_log_format.h" > > > diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h > > > index ae1e66fa3f61..1631cf4546f2 100644 > > > --- a/fs/xfs/xfs_linux.h > > > +++ b/fs/xfs/xfs_linux.h > > > @@ -26,6 +26,7 @@ typedef __u32 xfs_nlink_t; > > > #include > > > #include > > > +#include > > > #include > > > #include > > > #include > > > > > Looks, ok. Was moving the header include intentional? Just clean up maybe? > > Other than that, looks good. > > I can't speak for Dave, but I'll point out that memalloc_nofs_restore is > declared in linux/sched/mm.h, so the #include hoist makes the symbol > available to the aops code in such a manner that now it's available to > all the xfs code so that we don't have to remember this... *nod* That's historically how we've handled OS level includes - it keeps the XFS files to including XFS headers only and that makes things like userspace code syncs a lot easier. Cheers, Dave. -- Dave Chinner david@fromorbit.com