[PATCH v2 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 forever,
retrying on the same fault.

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

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 7201e848129a7..fa2b3d2ad3202 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, and reject a bad entry. */
 	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