From aa6ee4ab69293969867ab09b57546d226ace3d7a Mon Sep 17 00:00:00 2001
From: Brian Foster <bfoster@redhat.com>
Date: Fri, 1 Feb 2019 09:36:36 -0800
Subject: [PATCH] xfs: eof trim writeback mapping as soon as it is cached
Git-commit: aa6ee4ab69293969867ab09b57546d226ace3d7a
Patch-mainline: v5.0-rc6
References: bsc#1138019

The cached writeback mapping is EOF trimmed to try and avoid races
between post-eof block management and writeback that result in
sending cached data to a stale location. The cached mapping is
currently trimmed on the validation check, which leaves a race
window between the time the mapping is cached and when it is trimmed
against the current inode size.

For example, if a new mapping is cached by delalloc conversion on a
blocksize == page size fs, we could cycle various locks, perform
memory allocations, etc.  in the writeback codepath before the
associated mapping is eventually trimmed to i_size. This leaves
enough time for a post-eof truncate and file append before the
cached mapping is trimmed. The former event essentially invalidates
a range of the cached mapping and the latter bumps the inode size
such the trim on the next writepage event won't trim all of the
invalid blocks. fstest generic/464 reproduces this scenario
occasionally and causes a lost writeback and stale delalloc blocks
warning on inode inactivation.

To work around this problem, trim the cached writeback mapping as
soon as it is cached in addition to on subsequent validation checks.
This is a minor tweak to tighten the race window as much as possible
until a proper invalidation mechanism is available.

Fixes: 40214d128e07 ("xfs: trim writepage mapping to within eof")
Cc: <stable@vger.kernel.org> # v4.14+
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Acked-by: Anthony Iliopoulos <ailiopoulos@suse.com>

---
 fs/xfs/xfs_aops.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -495,6 +495,7 @@
 	}
 
 	wpc->imap = imap;
+	xfs_trim_extent_eof(&wpc->imap, ip);
 	trace_xfs_map_blocks_found(ip, offset, count, wpc->io_type, &imap);
 	return 0;
 allocate_blocks:
@@ -502,6 +503,7 @@
 	if (error)
 		return error;
 	wpc->imap = imap;
+	xfs_trim_extent_eof(&wpc->imap, ip);
 	trace_xfs_map_blocks_alloc(ip, offset, count, wpc->io_type, &imap);
 	return 0;
 }