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SubjectRe: [PATCH] mm: drop hotplug lock from lru_add_drain_all
On Tue 14-11-17 15:23:47, Michal Hocko wrote:
[...]
> +/*
> + * Doesn't need any cpu hotplug locking because we do rely on per-cpu
> + * kworkers being shut down before our page_alloc_cpu_dead callback is
> + * executed on the offlined cpu
> + */
> void lru_add_drain_all(void)
> {
> static DEFINE_MUTEX(lock);

Ble the part of the comment didn't go through

diff --git a/mm/swap.c b/mm/swap.c
index 8bfdcab9f83e..1ab8122d2d0c 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -688,6 +688,13 @@ static void lru_add_drain_per_cpu(struct work_struct *dummy)

static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);

+/*
+ * Doesn't need any cpu hotplug locking because we do rely on per-cpu
+ * kworkers being shut down before our page_alloc_cpu_dead callback is
+ * executed on the offlined cpu.
+ * Calling this function with cpu hotplug locks held can actually lead
+ * to obscure indirect dependencies via WQ context.
+ */
void lru_add_drain_all(void)
{
static DEFINE_MUTEX(lock);
--
Michal Hocko
SUSE Labs
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