maple_tree: do not hash pointers on dump in debug mode

Many maple tree values output when an mt_validate() or equivalent hits an
issue utilise tagged pointers, most notably parent nodes. Also some
pivots/slots contain meaningful values, output as pointers, such as the
index of the last entry with data for example.

All pointer values such as this are destroyed by kernel pointer hashing
rendering the debug output obtained from CONFIG_DEBUG_VM_MAPLE_TREE
considerably less usable.

Update this code to output the raw pointers using %px rather than %p when
CONFIG_DEBUG_VM_MAPLE_TREE is defined. This is justified, as the use of
this configuration flag indicates that this is a test environment.

Userland does not understand %px, so use %p there.

In an abundance of caution, if CONFIG_DEBUG_VM_MAPLE_TREE is not set, also
use %p to avoid exposing raw kernel pointers except when we are positive a
testing mode is enabled.

This was inspired by the investigation performed in recent debugging
efforts around a maple tree regression [0] where kernel pointer tagging had
to be disabled in order to obtain truly meaningful and useful data.

[0]:https://lore.kernel.org/all/20241001023402.3374-1-spasswolf@web.de/

Link: https://lkml.kernel.org/r/20241007115335.90104-1-lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

0 files changed, 0 insertions, 0 deletions