[PATCH v3 2/2] mm: fail the fault on a malformed swap entry instead of retrying it

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 forever,
retrying on the same fault.

Return VM_FAULT_SIGBUS (Bad access) for a malformed entry (pr_err() was
called at get_swap_device()).

Acked-by: Kairui Song <[email protected]>
Reviewed-by: Barry Song <[email protected]>
Signed-off-by: Breno Leitao <[email protected]>
---
 mm/memory.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index 03d8cf111d0be..d9db4f1ae6f8a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4956,8 +4956,11 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 
 	/* Prevent swapoff from happening to us, and reject a bad entry. */
 	si = get_swap_device(entry);
-	if (IS_ERR_OR_NULL(si))
+	if (IS_ERR_OR_NULL(si)) {
+		if (IS_ERR(si))
+			ret = VM_FAULT_SIGBUS;
 		goto out;
+	}
 
 	folio = swap_cache_get_folio(entry);
 	if (folio)

-- 
2.53.0-Meta