gfs2: Prevent recursive memory reclaim

In the Linux kernel, the following vulnerability has been resolved:

gfs2: Prevent recursive memory reclaim

Function new_inode() returns a new inode with inode->i_mapping->gfp_mask
set to GFP_HIGHUSER_MOVABLE. This value includes the __GFP_FS flag, so
allocations in that address space can recurse into filesystem memory
reclaim. We don't want that to happen because it can consume a
significant amount of stack memory.

Worse than that is that it can also deadlock: for example, in several
places, gfs2_unstuff_dinode() is called inside filesystem transactions.
This calls filemap_grab_folio(), which can allocate a new folio, which
can trigger memory reclaim. If memory reclaim recurses into the
filesystem and starts another transaction, a deadlock will ensue.

To fix these kinds of problems, prevent memory reclaim from recursing
into filesystem code by making sure that the gfp_mask of inode address
spaces doesn't include __GFP_FS.

The "meta" and resource group address spaces were already using GFP_NOFS
as their gfp_mask (which doesn't include __GFP_FS). The default value
of GFP_HIGHUSER_MOVABLE is less restrictive than GFP_NOFS, though. To
avoid being overly limiting, use the default value and only knock off
the __GFP_FS flag. I'm not sure if this will actually make a
difference, but it also shouldn't hurt.

This patch is loosely based on commit ad22c7a043c2 ("xfs: prevent stack
overflows from page cache allocation").

Fixes xfstest generic/273.