Return-Path: linux-nfs-owner@vger.kernel.org Received: from cantor2.suse.de ([195.135.220.15]:38819 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751554AbaDPESy (ORCPT ); Wed, 16 Apr 2014 00:18:54 -0400 From: NeilBrown To: linux-mm@kvack.org, linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Date: Wed, 16 Apr 2014 14:03:36 +1000 Subject: [PATCH 09/19] XFS: ensure xfs_file_*_read cannot deadlock in memory allocation. Cc: xfs@oss.sgi.com Message-ID: <20140416040336.10604.90380.stgit@notabene.brown> In-Reply-To: <20140416033623.10604.69237.stgit@notabene.brown> References: <20140416033623.10604.69237.stgit@notabene.brown> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Sender: linux-nfs-owner@vger.kernel.org List-ID: xfs_file_*_read holds an inode lock while calling a generic 'read' function. These functions perform read-ahead and are quite likely to allocate memory. So set PF_FSTRANS to ensure they avoid __GFP_FS and so don't recurse into a filesystem to free memory. This can be a problem with loop-back NFS mounts, if free_pages ends up wating in nfs_release_page(), and nfsd is blocked waiting for the lock that this code holds. This was found both by lockdep and as a real deadlock during testing. Signed-off-by: NeilBrown --- fs/xfs/xfs_file.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c index 64b48eade91d..88b33ef64668 100644 --- a/fs/xfs/xfs_file.c +++ b/fs/xfs/xfs_file.c @@ -243,6 +243,7 @@ xfs_file_aio_read( ssize_t ret = 0; int ioflags = 0; xfs_fsize_t n; + unsigned int pflags; XFS_STATS_INC(xs_read_calls); @@ -290,6 +291,10 @@ xfs_file_aio_read( * proceeed concurrently without serialisation. */ xfs_rw_ilock(ip, XFS_IOLOCK_SHARED); + /* As we hold a lock, we must ensure that any allocation + * in generic_file_aio_read avoid __GFP_FS + */ + current_set_flags_nested(&pflags, PF_FSTRANS); if ((ioflags & IO_ISDIRECT) && inode->i_mapping->nrpages) { xfs_rw_iunlock(ip, XFS_IOLOCK_SHARED); xfs_rw_ilock(ip, XFS_IOLOCK_EXCL); @@ -313,6 +318,7 @@ xfs_file_aio_read( if (ret > 0) XFS_STATS_ADD(xs_read_bytes, ret); + current_restore_flags_nested(&pflags, PF_FSTRANS); xfs_rw_iunlock(ip, XFS_IOLOCK_SHARED); return ret; } @@ -328,6 +334,7 @@ xfs_file_splice_read( struct xfs_inode *ip = XFS_I(infilp->f_mapping->host); int ioflags = 0; ssize_t ret; + unsigned int pflags; XFS_STATS_INC(xs_read_calls); @@ -338,6 +345,10 @@ xfs_file_splice_read( return -EIO; xfs_rw_ilock(ip, XFS_IOLOCK_SHARED); + /* As we hold a lock, we must ensure that any allocation + * in generic_file_splice_read avoid __GFP_FS + */ + current_set_flags_nested(&pflags, PF_FSTRANS); trace_xfs_file_splice_read(ip, count, *ppos, ioflags); @@ -345,6 +356,7 @@ xfs_file_splice_read( if (ret > 0) XFS_STATS_ADD(xs_read_bytes, ret); + current_restore_flags_nested(&pflags, PF_FSTRANS); xfs_rw_iunlock(ip, XFS_IOLOCK_SHARED); return ret; }