[176/200] NFS: Fix another nfs_wb_page() deadlock

Greg KH
2010-07-01T21:31:39Z

2.6.34-stable review patch. If anyone has any objections, please let me know.

------------------

From: Trond Myklebust <Trond.Myklebust@netapp.com>

commit 0522f6adedd2736cbca3c0e16ca51df668993eee upstream.

J.R. Okajima reports that the call to sync_inode() in nfs_wb_page() can
deadlock with other writeback flush calls. It boils down to the fact
that we cannot ever call writeback_single_inode() while holding a page
lock (even if we do set nr_to_write to zero) since another process may
already be waiting in the call to do_writepages(), and so will deny us
the I_SYNC lock.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/nfs/write.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1518,14 +1518,17 @@ int nfs_wb_page(struct inode *inode, str
};
int ret;

- while(PagePrivate(page)) {
+ for (;;) {
wait_on_page_writeback(page);
if (clear_page_dirty_for_io(page)) {
ret = nfs_writepage_locked(page, &wbc);
if (ret < 0)
goto out_error;
+ continue;
}
- ret = sync_inode(inode, &wbc);
+ if (!PagePrivate(page))
+ break;
+ ret = nfs_commit_inode(inode, FLUSH_SYNC);
if (ret < 0)
goto out_error;
}