tree 05378e180b27949a8939eb89adf5423ee66718b0
parent e22a6754abda4ab563fce3f3241e71a8c917c979
author Trond Myklebust <trond.myklebust@primarydata.com> 1493672816 -0400
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> 1521885621 +0100

pNFS: Fix a deadlock when coalescing writes and returning the layout


[ Upstream commit 61f454e30c18a28924e96be12592c0d5e24bcc81 ]

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 <trond.myklebust@primarydata.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>