4.9-stable review patch. If anyone has any objections, please let me know.
------------------ From: Jan Kara <[email protected]> [ Upstream commit e3fce68cdbed297d927e993b3ea7b8b1cee545da ] Currently dax_iomap_rw() takes care of invalidating page tables and evicting hole pages from the radix tree when write(2) to the file happens. This invalidation is only necessary when there is some block allocation resulting from write(2). Furthermore in current place the invalidation is racy wrt page fault instantiating a hole page just after we have invalidated it. So perform the page invalidation inside dax_iomap_actor() where we can do it only when really necessary and after blocks have been allocated so nobody will be instantiating new hole pages anymore. Reviewed-by: Christoph Hellwig <[email protected]> Reviewed-by: Ross Zwisler <[email protected]> Signed-off-by: Jan Kara <[email protected]> Signed-off-by: Dan Williams <[email protected]> Signed-off-by: Sasha Levin <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- fs/dax.c | 28 +++++++++++----------------- 1 file changed, 11 insertions(+), 17 deletions(-) --- a/fs/dax.c +++ b/fs/dax.c @@ -1265,6 +1265,17 @@ iomap_dax_actor(struct inode *inode, lof if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED)) return -EIO; + /* + * Write can allocate block for an area which has a hole page mapped + * into page tables. We have to tear down these mappings so that data + * written by write(2) is visible in mmap. + */ + if ((iomap->flags & IOMAP_F_NEW) && inode->i_mapping->nrpages) { + invalidate_inode_pages2_range(inode->i_mapping, + pos >> PAGE_SHIFT, + (end - 1) >> PAGE_SHIFT); + } + while (pos < end) { unsigned offset = pos & (PAGE_SIZE - 1); struct blk_dax_ctl dax = { 0 }; @@ -1329,23 +1340,6 @@ iomap_dax_rw(struct kiocb *iocb, struct if (iov_iter_rw(iter) == WRITE) flags |= IOMAP_WRITE; - /* - * Yes, even DAX files can have page cache attached to them: A zeroed - * page is inserted into the pagecache when we have to serve a write - * fault on a hole. It should never be dirtied and can simply be - * dropped from the pagecache once we get real data for the page. - * - * XXX: This is racy against mmap, and there's nothing we can do about - * it. We'll eventually need to shift this down even further so that - * we can check if we allocated blocks over a hole first. - */ - if (mapping->nrpages) { - ret = invalidate_inode_pages2_range(mapping, - pos >> PAGE_SHIFT, - (pos + iov_iter_count(iter) - 1) >> PAGE_SHIFT); - WARN_ON_ONCE(ret); - } - while (iov_iter_count(iter)) { ret = iomap_apply(inode, pos, iov_iter_count(iter), flags, ops, iter, iomap_dax_actor);
