zonefs: Always invalidate last cached page on append write

When a direct append write is executed, the append offset may correspond
to the last page of a sequential file inode which might have been cached
already by buffered reads, page faults with mmap-read or non-direct
readahead. To ensure that the on-disk and cached data is consistant for
such last cached page, make sure to always invalidate it in
zonefs_file_dio_append(). If the invalidation fails, return -EBUSY to
userspace to differentiate from IO errors.

This invalidation will always be a no-op when the FS block size (device
zone write granularity) is equal to the page size (e.g. 4K).
Reported-by: Hans Holmberg <Hans.Holmberg@wdc.com>
Fixes: 02ef12a6 ("zonefs: use REQ_OP_ZONE_APPEND for sync DIO")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Tested-by: Hans Holmberg <hans.holmberg@wdc.com>

fs/zonefs/file.c

@@ -382,6 +382,7 @@ static ssize_t zonefs_file_dio_append(struct kiocb *iocb, struct iov_iter *from)
 	struct zonefs_zone *z = zonefs_inode_zone(inode);
 	struct block_device *bdev = inode->i_sb->s_bdev;
 	unsigned int max = bdev_max_zone_append_sectors(bdev);
+	pgoff_t start, end;
 	struct bio *bio;
 	ssize_t size = 0;
 	int nr_pages;
@@ -390,6 +391,19 @@ static ssize_t zonefs_file_dio_append(struct kiocb *iocb, struct iov_iter *from)
 	max = ALIGN_DOWN(max << SECTOR_SHIFT, inode->i_sb->s_blocksize);
 	iov_iter_truncate(from, max);
 
+	/*
+	 * If the inode block size (zone write granularity) is smaller than the
+	 * page size, we may be appending data belonging to the last page of the
+	 * inode straddling inode->i_size, with that page already cached due to
+	 * a buffered read or readahead. So make sure to invalidate that page.
+	 * This will always be a no-op for the case where the block size is
+	 * equal to the page size.
+	 */
+	start = iocb->ki_pos >> PAGE_SHIFT;
+	end = (iocb->ki_pos + iov_iter_count(from) - 1) >> PAGE_SHIFT;
+	if (invalidate_inode_pages2_range(inode->i_mapping, start, end))
+		return -EBUSY;
+
 	nr_pages = iov_iter_npages(from, BIO_MAX_VECS);
 	if (!nr_pages)
 		return 0;