mm/mmap: clean up validate_mm() calls

Patch series "More strict maple tree lockdep", v2.

Linus asked for more strict maple tree lockdep checking [1] and for them
to resume the normal path through Andrews tree.

This series of patches adds checks to ensure the lock is held in write
mode during the write path of the maple tree instead of checking if it's
held at all.

It also reduces the validate_mm() calls by consolidating into commonly
used functions (patch 0001), and removes the necessity of holding the lock
on the detached tree during munmap() operations.


This patch (of 4):

validate_mm() calls are too spread out and duplicated in numerous
locations.  Also, now that the stack write is done under the write lock,
it is not necessary to validate the mm prior to write operations.

Add a validate_mm() to the stack expansions, and to vma_complete() so
that numerous others may be dropped.

Note that vma_link() (and also insert_vm_struct() by call path) already
call validate_mm().

vma_merge() also had an unnecessary call to vma_iter_free() since the
logic change to abort earlier if no merging is necessary.

Drop extra validate_mm() calls at the start of functions and error paths
which won't write to the tree.

Relocate the validate_mm() call in the do_brk_flags() to avoid
re-running the same test when vma_complete() is used.

The call within the error path of mmap_region() is left intentionally
because of the complexity of the function and the potential of drivers
modifying the tree.

Link: https://lkml.kernel.org/r/20230714195551.894800-1-Liam.Howlett@oracle.com
Link: https://lkml.kernel.org/r/20230714195551.894800-2-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oliver Sang <oliver.sang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>