We've met softlockup with "CONFIG_PREEMPT_NONE=y", when
the target memcg doesn't have any reclaimable memory.
It can be easily reproduced as below:
watchdog: BUG: soft lockup - CPU#0 stuck for 111s![memcg_test:2204]
CPU: 0 PID: 2204 Comm: memcg_test Not tainted 5.9.0-rc2+ #12
Call Trace:
shrink_lruvec+0x49f/0x640
shrink_node+0x2a6/0x6f0
do_try_to_free_pages+0xe9/0x3e0
try_to_free_mem_cgroup_pages+0xef/0x1f0
try_charge+0x2c1/0x750
mem_cgroup_charge+0xd7/0x240
__add_to_page_cache_locked+0x2fd/0x370
add_to_page_cache_lru+0x4a/0xc0
pagecache_get_page+0x10b/0x2f0
filemap_fault+0x661/0xad0
ext4_filemap_fault+0x2c/0x40
__do_fault+0x4d/0xf9
handle_mm_fault+0x1080/0x1790
It only happens on our 1-vcpu instances, because there's no chance
for oom reaper to run to reclaim the to-be-killed process.
Add cond_resched() in such cases at the beginning of shrink_lruvec()
to give up the cpu to others.
Signed-off-by: Xunlei Pang <xlpang@xxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 99e1796..349a88e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2449,6 +2449,12 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
scan_adjusted = (!cgroup_reclaim(sc) && !current_is_kswapd() &&
sc->priority == DEF_PRIORITY);
+ /* memcg reclaim may run into no reclaimable lru pages */
+ if (nr[LRU_ACTIVE_FILE] == 0 &&
+ nr[LRU_INACTIVE_FILE] == 0 &&
+ nr[LRU_INACTIVE_ANON] == 0)
+ cond_resched();
+
blk_start_plug(&plug);
while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
nr[LRU_INACTIVE_FILE]) {
--
1.8.3.1
