fuse: disable FOPEN_PARALLEL_DIRECT_WRITES with FUSE_DIRECT_IO_ALLOW_…

…MMAP

The new fuse init flag FUSE_DIRECT_IO_ALLOW_MMAP breaks assumptions made by
FOPEN_PARALLEL_DIRECT_WRITES and causes test generic/095 to hit
BUG_ON(fi->writectr < 0) assertions in fuse_set_nowrite():

generic/095 5s ...
  kernel BUG at fs/fuse/dir.c:1756!
...
  ? fuse_set_nowrite+0x3d/0xdd
  ? do_raw_spin_unlock+0x88/0x8f
  ? _raw_spin_unlock+0x2d/0x43
  ? fuse_range_is_writeback+0x71/0x84
  fuse_sync_writes+0xf/0x19
  fuse_direct_io+0x167/0x5bd
  fuse_direct_write_iter+0xf0/0x146

Auto disable FOPEN_PARALLEL_DIRECT_WRITES when server negotiated
FUSE_DIRECT_IO_ALLOW_MMAP.

Fixes: e78662e ("fuse: add a new fuse init flag to relax restrictions in no cache mode")
Cc: <[email protected]> # v6.6
Signed-off-by: Amir Goldstein <[email protected]>
Signed-off-by: Miklos Szeredi <[email protected]>

fs/fuse/file.c

@@ -1574,13 +1574,15 @@ static ssize_t fuse_direct_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	ssize_t res;
 	bool exclusive_lock =
 		!(ff->open_flags & FOPEN_PARALLEL_DIRECT_WRITES) ||
+		get_fuse_conn(inode)->direct_io_allow_mmap ||
 		iocb->ki_flags & IOCB_APPEND ||
 		fuse_direct_write_extending_i_size(iocb, from);
 
 	/*
 	 * Take exclusive lock if
 	 * - Parallel direct writes are disabled - a user space decision
 	 * - Parallel direct writes are enabled and i_size is being extended.
+	 * - Shared mmap on direct_io file is supported (FUSE_DIRECT_IO_ALLOW_MMAP).
 	 *   This might not be needed at all, but needs further investigation.
 	 */
 	if (exclusive_lock)