mm: fix unkillable fault loop on MAP_DROPPABLE memory

handle_mm_fault() suppresses VM_FAULT_OOM for VM_DROPPABLE mappings.

For user-mode faults, pending signals are processed before retrying the
access. Kernel-mode faults on user buffers instead return directly to
the faulting instruction.

With persistent allocation failures (esp. memcg limits), a syscall,
such as write(), can therefore loop while not dropping locks.

Only suppress VM_FAULT_OOM when FAULT_FLAG_USER is set, allowing
kernel-mode faults and GUP to fail and signal allocation errors.

Fix generated by an LLM and sent by Chris Mason in private.

Fixes: 9651fcedf7b9 ("mm: add MAP_DROPPABLE for designating always lazily freeable mappings")
Cc: stable@vger.kernel.org
Signed-off-by: Chris Mason <mason@kernel.org>
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
[ david: simplify description ]
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Link: https://patch.msgid.link/20261031-fixes_core-v3-37-d6437171ecc3@kernel.org
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>

0 files changed, 0 insertions, 0 deletions