From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from aserp2130.oracle.com ([141.146.126.79]:35650 "EHLO aserp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935004AbeFGOqg (ORCPT ); Thu, 7 Jun 2018 10:46:36 -0400 Date: Thu, 7 Jun 2018 07:46:31 -0700 From: "Darrick J. Wong" Subject: Re: [PATCH 2/2] xfs: xfs_reflink_convert_cow() memory allocation deadlock Message-ID: <20180607144631.GC25007@magnolia> References: <20180607052132.6207-1-david@fromorbit.com> <20180607052132.6207-3-david@fromorbit.com> <77a374f5-3d05-5d53-0253-265c801eb2f8@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <77a374f5-3d05-5d53-0253-265c801eb2f8@oracle.com> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Allison Henderson Cc: Dave Chinner , linux-xfs@vger.kernel.org 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... Reviewed-by: Darrick J. Wong --D > > Reviewed-by: Allison Henderson > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html