[PATCH 4.19 37/89] mm/swapfile: add cond_resched() in get_swap_pages()

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From: Longlong Xia <xialonglong1@xxxxxxxxxx>

commit 7717fc1a12f88701573f9ed897cc4f6699c661e3 upstream.

The softlockup still occurs in get_swap_pages() under memory pressure.  64
CPU cores, 64GB memory, and 28 zram devices, the disksize of each zram
device is 50MB with same priority as si.  Use the stress-ng tool to
increase memory pressure, causing the system to oom frequently.

The plist_for_each_entry_safe() loops in get_swap_pages() could reach tens
of thousands of times to find available space (extreme case:
cond_resched() is not called in scan_swap_map_slots()).  Let's add
cond_resched() into get_swap_pages() when failed to find available space
to avoid softlockup.

Link: https://lkml.kernel.org/r/20230128094757.1060525-1-xialonglong1@xxxxxxxxxx
Signed-off-by: Longlong Xia <xialonglong1@xxxxxxxxxx>
Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Chen Wandun <chenwandun@xxxxxxxxxx>
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Nanyong Sun <sunnanyong@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 mm/swapfile.c |    1 +
 1 file changed, 1 insertion(+)

--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1008,6 +1008,7 @@ start_over:
 			goto check_out;
 		pr_debug("scan_swap_map of si %d failed to find offset\n",
 			si->type);
+		cond_resched();
 
 		spin_lock(&swap_avail_lock);
 nextsi:





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