xfs: make inode flush at ENOSPC synchronous

When we are writing to a single file and hit ENOSPC, we trigger a background
flush of the inode and try again.  Because we hold page locks and the iolock,
the flush won't proceed until after we release these locks. This occurs once
we've given up and ENOSPC has been reported. Hence if this one is the only
dirty inode in the system, we'll get an ENOSPC prematurely.

To fix this, remove the async flush from the allocation routines and move
it to the top of the write path where we can do a synchronous flush
and retry the write again. Only retry once as a second ENOSPC indicates
that we really are ENOSPC.

This avoids a page cache deadlock when trying to do this flush synchronously
in the allocation layer that was identified by Mikulas Patocka.

Signed-off-by: Dave Chinner <david@fromorbit.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

1 files changed, 17 insertions, 1 deletions

diff --git a/fs/xfs/linux-2.6/xfs_lrw.c b/fs/xfs/linux-2.6/xfs_lrw.c
index 7e90daa0d1d1..9142192ccbe6 100644
--- a/fs/xfs/linux-2.6/xfs_lrw.c
+++ b/fs/xfs/linux-2.6/xfs_lrw.c
@@ -751,10 +751,26 @@ start:
 			goto relock;
 		}
 	} else {
+		int enospc = 0;
+		ssize_t ret2 = 0;
+
+write_retry:
 		xfs_rw_enter_trace(XFS_WRITE_ENTER, xip, (void *)iovp, segs,
 				*offset, ioflags);
-		ret = generic_file_buffered_write(iocb, iovp, segs,
+		ret2 = generic_file_buffered_write(iocb, iovp, segs,
 				pos, offset, count, ret);
+		/*
+		 * if we just got an ENOSPC, flush the inode now we
+		 * aren't holding any page locks and retry *once*
+		 */
+		if (ret2 == -ENOSPC && !enospc) {
+			error = xfs_flush_pages(xip, 0, -1, 0, FI_NONE);
+			if (error)
+				goto out_unlock_internal;
+			enospc = 1;
+			goto write_retry;
+		}
+		ret = ret2;
 	}
 
 	current->backing_dev_info = NULL;