[PATCH v4 26/33] mm: prevent do_swap_page from handling page faults under VMA lock

[Suren Baghdasaryan]

Due to the possibility of do_swap_page dropping mmap_lock, abort fault
handling under VMA lock and retry holding mmap_lock. This can be handled
more gracefully in the future.

Signed-off-by: Suren Baghdasaryan <surenb at google.com>
Reviewed-by: Laurent Dufour <laurent.dufour at fr.ibm.com>
---
 mm/memory.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index 8855846a361b..af3c2c59cd11 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3689,6 +3689,11 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	if (!pte_unmap_same(vmf))
 		goto out;
 
+	if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
+		ret = VM_FAULT_RETRY;
+		goto out;
+	}
+
 	entry = pte_to_swp_entry(vmf->orig_pte);
 	if (unlikely(non_swap_entry(entry))) {
 		if (is_migration_entry(entry)) {
-- 
2.39.2.722.g9855ee24e9-goog