[PATCH 3/3] mm: fail the fault on a malformed swap entry instead of retrying it

[Breno Leitao <leitao@debian.org>]

do_swap_page() returns 0 when get_swap_device() fails, which the fault
handler reads as "handled". For an entry that can never become valid
the retry takes the same fault again, so the thread spins until it is
killed.

Return VM_FAULT_SIGBUS for a malformed entry, as the sibling arm
already does for an unrecognised non-swap entry. A NULL return still
means swapoff, which is still worth retrying.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 mm/memory.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index 4238778b66c42..2842cd976f1d3 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4957,6 +4957,9 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	/* Prevent swapoff from happening to us. */
 	si = get_swap_device(entry);
 	if (IS_ERR_OR_NULL(si)) {
+		/* A malformed entry never becomes valid, so don't retry it. */
+		if (IS_ERR(si))
+			ret = VM_FAULT_SIGBUS;
 		si = NULL;
 		goto out;
 	}

-- 
2.53.0-Meta