Messages in this thread | | | Date | Wed, 24 Aug 2022 17:51:49 +0800 | Subject | Re: [PATCH 2/2] mm: slince possible data races about pgdat->kswapd | From | Kefeng Wang <> |
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On 2022/8/24 16:24, David Hildenbrand wrote: > On 24.08.22 09:19, Kefeng Wang wrote: >> The pgdat->kswapd could be accessed concurrently by kswapd_run() and >> kcompactd(), it don't be protected by any lock, which could leads to >> data races, adding READ/WRITE_ONCE() to slince it. > Okay, I think this patch here makes it clearer that we really just want > proper synchronization instead of hacking around it. > > What speaks against protecting pgdat->kswapd this using some proper > locking primitive?
So add a new lock into struct pglist_data to protect pgdat->kswapd,other
option, thanks.
>> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com> >> --- >> mm/compaction.c | 4 +++- >> mm/vmscan.c | 8 ++++---- >> 2 files changed, 7 insertions(+), 5 deletions(-) >> >> diff --git a/mm/compaction.c b/mm/compaction.c >> index 640fa76228dd..aa1cfe47f046 100644 >> --- a/mm/compaction.c >> +++ b/mm/compaction.c >> @@ -1983,7 +1983,9 @@ static inline bool is_via_compact_memory(int order) >> >> static bool kswapd_is_running(pg_data_t *pgdat) >> { >> - return pgdat->kswapd && task_is_running(pgdat->kswapd); >> + struct task_struct *t = READ_ONCE(pgdat->kswapd); >> + >> + return t && task_is_running(t); >> } >> >> /* >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index 08c6497f76c3..65b19ca8c8ee 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -4644,7 +4644,7 @@ void kswapd_run(int nid) >> pg_data_t *pgdat = NODE_DATA(nid); >> struct task_struct *t; >> >> - if (pgdat->kswapd) >> + if (READ_ONCE(pgdat->kswapd)) >> return; >> >> t = kthread_run(kswapd, pgdat, "kswapd%d", nid); >> @@ -4653,7 +4653,7 @@ void kswapd_run(int nid) >> BUG_ON(system_state < SYSTEM_RUNNING); >> pr_err("Failed to start kswapd on node %d\n", nid); >> } else { >> - pgdat->kswapd = t; >> + WRITE_ONCE(pgdat->kswapd, t); >> } >> } >> >> @@ -4663,11 +4663,11 @@ void kswapd_run(int nid) >> */ >> void kswapd_stop(int nid) >> { >> - struct task_struct *kswapd = NODE_DATA(nid)->kswapd; >> + struct task_struct *kswapd = READ_ONCE(NODE_DATA(nid)->kswapd); >> >> if (kswapd) { >> kthread_stop(kswapd); >> - NODE_DATA(nid)->kswapd = NULL; >> + WRITE_ONCE(NODE_DATA(nid)->kswapd, NULL); >> } >> } >> >
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