From: Josef Bacik <[email protected]>
When the last memory of a zone goes offline, zone_pcp_reset() frees
zone->per_cpu_pageset and zone->per_cpu_zonestats. Nothing waits for those
who found the zone populated and still use the two pointers. They take
neither the memory hotplug lock nor any other lock which offline_pages()
holds, and some of them can sleep:
CPU0 vmstat_update() CPU1 offline_pages()
refresh_cpu_vm_stats()
for_each_populated_zone(zone)
pcp = zone->per_cpu_pageset
cond_resched()
adjust_present_page_count()
zone_pcp_reset(zone)
free_percpu(zone->per_cpu_pageset)
decay_pcp_high(zone, pcp)
__this_cpu_write(pcp->expire, 0)
The same goes for drain_all_pages(NULL), which takes pcp->lock, for
zone_pcp_update(), show_free_areas() and the readers and writers of the
zonestats. If the per-cpu memory has got a new owner in the meantime, it
is corrupted.
The pagesets are only freed because setup_zone_pageset() would otherwise
leak them when the zone gets memory again. Keep them instead and let
setup_zone_pageset() and zone_pcp_init() use them again, like it is done
with pgdat->per_cpu_nodestats. Their lists are empty, and their limits
have been calculated for a zone without memory by the
init_per_zone_wmark_min() of offline_pages(), which is what
setup_zone_pageset() would come up with as well.
Fixes: 340175b7d14d ("mm/hotplug: free zone->pageset when a zone becomes empty")
Cc: <[email protected]>
Assisted-by: LLM
Signed-off-by: Josef Bacik <[email protected]>
Signed-off-by: David Hildenbrand (Arm) <[email protected]>
Reviewed-by: Johannes Weiner <[email protected]>
Signed-off-by: Vlastimil Babka (SUSE) <[email protected]>
Signed-off-by: Gregory Price (Meta) <[email protected]>
---
mm/page_alloc.c | 20 ++++++++++++++------
1 file changed, 14 insertions(+), 6 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f1048168c90c..1850a41f24f7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6308,6 +6308,10 @@ void __meminit setup_zone_pageset(struct zone *zone)
{
int cpu;
+ /* The zone has been populated before, see zone_pcp_reset(). */
+ if (zone->per_cpu_pageset != &boot_pageset)
+ return;
+
/* Size may be 0 on !SMP && !NUMA */
if (sizeof(struct per_cpu_zonestat) > 0)
zone->per_cpu_zonestats = alloc_percpu(struct per_cpu_zonestat);
@@ -6400,6 +6404,10 @@ void __init setup_per_cpu_pageset(void)
__meminit void zone_pcp_init(struct zone *zone)
{
+ /* A node which is added again, see zone_pcp_reset(). */
+ if (zone->per_cpu_pageset && zone->per_cpu_pageset != &boot_pageset)
+ return;
+
/*
* per cpu subsystem is not up at this point. The following code
* relies on the ability of the linker to provide the
@@ -7680,6 +7688,12 @@ void zone_pcp_enable(struct zone *zone)
mutex_unlock(&pcp_batch_high_lock);
}
+/*
+ * The zone has become empty. Its pagesets and zonestats are not freed: nothing
+ * keeps somebody who found the zone populated, such as refresh_cpu_vm_stats()
+ * or drain_all_pages(), from still using them. They are used again when the
+ * zone gets memory again.
+ */
void zone_pcp_reset(struct zone *zone)
{
int cpu;
@@ -7690,12 +7704,6 @@ void zone_pcp_reset(struct zone *zone)
pzstats = per_cpu_ptr(zone->per_cpu_zonestats, cpu);
drain_zonestat(zone, pzstats);
}
- free_percpu(zone->per_cpu_pageset);
- zone->per_cpu_pageset = &boot_pageset;
- if (zone->per_cpu_zonestats != &boot_zonestats) {
- free_percpu(zone->per_cpu_zonestats);
- zone->per_cpu_zonestats = &boot_zonestats;
- }
}
}
--
2.56.0
