[PATCH] mm: swap: Avoid infinite loop if no valid swap entry found during do_swap_page

[Wupeng Ma <mawupeng1@xxxxxxxxxx>]

From: Ma Wupeng <mawupeng1@xxxxxxxxxx>

During our test, infinite loop is produced during #PF will lead to infinite
error log as follow:

   get_swap_device: Bad swap file entry 114000000

Digging into the source, we found that the swap entry is invalid due to
unknown reason, and this lead to invalid swap_info_struct. Excessive log
printing can fill up the prioritized log space, leading to the purging of
originally valid logs and hindering problem troubleshooting. To make this
more robust, kill this task.

Signed-off-by: Ma Wupeng <mawupeng1@xxxxxxxxxx>
---
 include/linux/swap.h | 1 +
 mm/memory.c          | 9 ++++++++-
 mm/swapfile.c        | 2 +-
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index b13b72645db3..0fa39cf66bc4 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -508,6 +508,7 @@ struct backing_dev_info;
 extern int init_swap_address_space(unsigned int type, unsigned long nr_pages);
 extern void exit_swap_address_space(unsigned int type);
 extern struct swap_info_struct *get_swap_device(swp_entry_t entry);
+struct swap_info_struct *_swap_info_get(swp_entry_t entry);
 sector_t swap_folio_sector(struct folio *folio);
 
 static inline void put_swap_device(struct swap_info_struct *si)
diff --git a/mm/memory.c b/mm/memory.c
index b4d3d4893267..2d36e5a644d1 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4365,8 +4365,15 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 
 	/* Prevent swapoff from happening to us. */
 	si = get_swap_device(entry);
-	if (unlikely(!si))
+	if (unlikely(!si)) {
+		if (unlikely(!_swap_info_get(entry)))
+			/*
+			 * return VM_FAULT_SIGBUS for invalid swap entry to
+			 * avoid infinite #PF.
+			 */
+			ret = VM_FAULT_SIGBUS;
 		goto out;
+	}
 
 	folio = swap_cache_get_folio(entry, vma, vmf->address);
 	if (folio)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index ba19430dd4ea..8f580eff0ecb 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1287,7 +1287,7 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
 	return n_ret;
 }
 
-static struct swap_info_struct *_swap_info_get(swp_entry_t entry)
+struct swap_info_struct *_swap_info_get(swp_entry_t entry)
 {
 	struct swap_info_struct *si;
 	unsigned long offset;
-- 
2.43.0