From: NeilBrown <neilb@suse.de>
Date: Fri, 29 Oct 2021 13:35:56 +1100
Subject: [PATCH] MM: reclaim mustn't enter FS for swap-over-NFS
Patch-mainline: Not yet - undergoing review
References: bsc#1191876

If swap-out is using filesystem operations (SWP_FS_OPS), then it is not
safe to enter the FS for reclaim.
So only down-grade the requirement for swap pages to __GFP_IO after
checking that SWP_FS_OPS are not being used.

Signed-off-by: NeilBrown <neilb@suse.de>
Acked-by: NeilBrown <neilb@suse.com>
Signed-off-by: Bogdan Lezhepekov <blezhepekov@suse.de>

---
 mm/vmscan.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1439,7 +1439,11 @@ static unsigned int shrink_page_list(str
 			goto keep_locked;
 
 		may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
-			(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
+			(PageSwapCache(page) &&
+#ifdef CONFIG_SWAP
+			 !(page_swap_info(page)->flags & SWP_FS_OPS) &&
+#endif
+			 (sc->gfp_mask & __GFP_IO));
 
 		/*
 		 * The number of dirty pages determines if a node is marked
@@ -1596,7 +1600,12 @@ static unsigned int shrink_page_list(str
 						goto activate_locked_split;
 				}
 
-				may_enter_fs = true;
+				if ((sc->gfp_mask & __GFP_FS) 
+#ifdef CONFIG_SWAP
+				    || !(page_swap_info(page)->flags & SWP_FS_OPS)
+#endif
+				    )
+					may_enter_fs = true;
 
 				/* Adding to swap updated mapping */
 				mapping = page_mapping(page);