mm: add cond_resched() in swapin_walk_pmd_entry()

When handling MADV_WILLNEED in madvise(), a soflockup may occurr in
swapin_walk_pmd_entry() if swapping in lots of memory on a slow device. 
Add a cond_resched() to avoid the possible softlockup.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 1998cc048901 ("mm: make madvise(MADV_WILLNEED) support swap file prefetch")
Signed-off-by: Kefeng Wang <[email protected]>
Cc: Shaohua Li <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Rik van Riel <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 1 insertions, 0 deletions

diff --git a/mm/madvise.c b/mm/madvise.c
index 2573ea3ed684..b7d9b1a1c135 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -223,6 +223,7 @@ static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,
 			put_page(page);
 	}
 	swap_read_unplug(splug);
+	cond_resched();
 
 	return 0;
 }