This is a note to let you know that I've just added the patch titled
pNFS: Fix a deadlock when coalescing writes and returning the layout
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
pnfs-fix-a-deadlock-when-coalescing-writes-and-returning-the-layout.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Thu Mar 22 14:40:24 CET 2018
From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Date: Mon, 1 May 2017 17:06:56 -0400
Subject: pNFS: Fix a deadlock when coalescing writes and returning the layout
From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
[ 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@xxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/nfs/pnfs.c | 2 --
1 file changed, 2 deletions(-)
--- a/fs/nfs/pnfs.c
+++ b/fs/nfs/pnfs.c
@@ -1953,8 +1953,6 @@ void pnfs_error_mark_layout_for_return(s
spin_lock(&inode->i_lock);
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()
Patches currently in stable-queue which might be from trond.myklebust@xxxxxxxxxxxxxxx are
queue-4.9/pnfs-fix-use-after-free-issues-in-pnfs_do_read.patch
queue-4.9/pnfs-fix-a-deadlock-when-coalescing-writes-and-returning-the-layout.patch
queue-4.9/nfs-fix-missing-pg_cleanup-after-nfs_pageio_cond_complete.patch