Return-Path: Received: from mail-io0-f194.google.com ([209.85.223.194]:33210 "EHLO mail-io0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750803AbdEBQiT (ORCPT ); Tue, 2 May 2017 12:38:19 -0400 Received: by mail-io0-f194.google.com with SMTP id o22so7015626iod.0 for ; Tue, 02 May 2017 09:38:19 -0700 (PDT) From: Trond Myklebust To: linux-nfs@vger.kernel.org Subject: [PATCH 2/3] pNFS: Fix a deadlock when coalescing writes and returning the layout Date: Tue, 2 May 2017 12:38:08 -0400 Message-Id: <20170502163812.6211-5-trond.myklebust@primarydata.com> In-Reply-To: <20170502163812.6211-4-trond.myklebust@primarydata.com> References: <20170502163812.6211-1-trond.myklebust@primarydata.com> <20170502163812.6211-2-trond.myklebust@primarydata.com> <20170502163812.6211-3-trond.myklebust@primarydata.com> <20170502163812.6211-4-trond.myklebust@primarydata.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: Consider the following deadlock: Process P1 Process P2 Process P3 ========== ========== ========== lock_page(page) lseg = pnfs_update_layout(inode) lo = NFS_I(inode)->layout pnfs_error_mark_layout_for_return(lo) lock_page(page) lseg = pnfs_update_layout(inode) In this scenario, - P1 has declared the layout to be in error, but P2 holds a reference to a layout segment on that inode, so the layoutreturn is deferred. - P2 is waiting for a page lock held by P3. - P3 is asking for a new layout segment, but is blocked waiting for the layoutreturn. The fix is to ensure that pnfs_error_mark_layout_for_return() does not set the NFS_LAYOUT_RETURN flag, which blocks P3. Instead, we allow the latter to call LAYOUTGET so that it can make progress and unblock P2. Signed-off-by: Trond Myklebust --- fs/nfs/pnfs.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c index cea1e838efae..adc6ec28d4b5 100644 --- a/fs/nfs/pnfs.c +++ b/fs/nfs/pnfs.c @@ -2063,8 +2063,6 @@ void pnfs_error_mark_layout_for_return(struct inode *inode, return; } pnfs_set_plh_return_info(lo, range.iomode, 0); - /* Block LAYOUTGET */ - set_bit(NFS_LAYOUT_RETURN, &lo->plh_flags); /* * mark all matching lsegs so that we are sure to have no live * segments at hand when sending layoutreturn. See pnfs_put_lseg() -- 2.9.3