| Message ID | 20240723064428.1179519-1-lizhijian@fujitsu.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v3] mm/page_alloc: Fix pcp->count race between drain_pages_zone() vs __rmqueue_pcplist() | expand |
On 7/23/24 8:44 AM, Li Zhijian wrote: > It's expected that no page should be left in pcp_list after calling > zone_pcp_disable() in offline_pages(). Previously, it's observed that > offline_pages() gets stuck [1] due to some pages remaining in pcp_list. > > Cause: > There is a race condition between drain_pages_zone() and __rmqueue_pcplist() > involving the pcp->count variable. See below scenario: > > CPU0 CPU1 > ---------------- --------------- > spin_lock(&pcp->lock); > __rmqueue_pcplist() { > zone_pcp_disable() { > /* list is empty */ > if (list_empty(list)) { > /* add pages to pcp_list */ > alloced = rmqueue_bulk() > mutex_lock(&pcp_batch_high_lock) > ... > __drain_all_pages() { > drain_pages_zone() { > /* read pcp->count, it's 0 here */ > count = READ_ONCE(pcp->count) > /* 0 means nothing to drain */ > /* update pcp->count */ > pcp->count += alloced << order; > ... > ... > spin_unlock(&pcp->lock); > > In this case, after calling zone_pcp_disable() though, there are still some > pages in pcp_list. And these pages in pcp_list are neither movable nor > isolated, offline_pages() gets stuck as a result. > > Solution: > Expand the scope of the pcp->lock to also protect pcp->count in > drain_pages_zone(), to ensure no pages are left in the pcp list after > zone_pcp_disable() > > [1] https://lore.kernel.org/linux-mm/6a07125f-e720-404c-b2f9-e55f3f166e85@fujitsu.com/ > > Cc: David Hildenbrand <david@redhat.com> > Cc: Vlastimil Babka (SUSE) <vbabka@kernel.org> > Reported-by: Yao Xingtao <yaoxt.fnst@fujitsu.com> > Signed-off-by: Li Zhijian <lizhijian@fujitsu.com> Fixes: 4b23a68f9536 ("mm/page_alloc: protect PCP lists with a spinlock") I'd also add a Cc: stable in this case Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Thanks! > --- > V3: > Read pcp->count in the loop with lock held to prevent unnecessary spin_lock() wasteful > V2: > - Narrow down the scope of the spin_lock() to limit the draining latency. # Vlastimil and David > - In above scenario, it's sufficient to read pcp->count once with lock held, and it fully fixed > my issue[1] in thounds runs(It happened in more than 5% before). > RFC: > https://lore.kernel.org/linux-mm/20240716073929.843277-1-lizhijian@fujitsu.com/ > Signed-off-by: Li Zhijian <lizhijian@fujitsu.com> > --- > mm/page_alloc.c | 18 +++++++++++------- > 1 file changed, 11 insertions(+), 7 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 9ecf99190ea2..a32289ec4768 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -2323,16 +2323,20 @@ void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp) > static void drain_pages_zone(unsigned int cpu, struct zone *zone) > { > struct per_cpu_pages *pcp = per_cpu_ptr(zone->per_cpu_pageset, cpu); > - int count = READ_ONCE(pcp->count); > - > - while (count) { > - int to_drain = min(count, pcp->batch << CONFIG_PCP_BATCH_SCALE_MAX); > - count -= to_drain; > + int count; > > + do { > spin_lock(&pcp->lock); > - free_pcppages_bulk(zone, to_drain, pcp, 0); > + count = pcp->count; > + if (count) { > + int to_drain = min(count, > + pcp->batch << CONFIG_PCP_BATCH_SCALE_MAX); > + > + free_pcppages_bulk(zone, to_drain, pcp, 0); > + count -= to_drain; > + } > spin_unlock(&pcp->lock); > - } > + } while (count); > } > > /*
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 9ecf99190ea2..a32289ec4768 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2323,16 +2323,20 @@ void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp) static void drain_pages_zone(unsigned int cpu, struct zone *zone) { struct per_cpu_pages *pcp = per_cpu_ptr(zone->per_cpu_pageset, cpu); - int count = READ_ONCE(pcp->count); - - while (count) { - int to_drain = min(count, pcp->batch << CONFIG_PCP_BATCH_SCALE_MAX); - count -= to_drain; + int count; + do { spin_lock(&pcp->lock); - free_pcppages_bulk(zone, to_drain, pcp, 0); + count = pcp->count; + if (count) { + int to_drain = min(count, + pcp->batch << CONFIG_PCP_BATCH_SCALE_MAX); + + free_pcppages_bulk(zone, to_drain, pcp, 0); + count -= to_drain; + } spin_unlock(&pcp->lock); - } + } while (count); } /*
It's expected that no page should be left in pcp_list after calling zone_pcp_disable() in offline_pages(). Previously, it's observed that offline_pages() gets stuck [1] due to some pages remaining in pcp_list. Cause: There is a race condition between drain_pages_zone() and __rmqueue_pcplist() involving the pcp->count variable. See below scenario: CPU0 CPU1 ---------------- --------------- spin_lock(&pcp->lock); __rmqueue_pcplist() { zone_pcp_disable() { /* list is empty */ if (list_empty(list)) { /* add pages to pcp_list */ alloced = rmqueue_bulk() mutex_lock(&pcp_batch_high_lock) ... __drain_all_pages() { drain_pages_zone() { /* read pcp->count, it's 0 here */ count = READ_ONCE(pcp->count) /* 0 means nothing to drain */ /* update pcp->count */ pcp->count += alloced << order; ... ... spin_unlock(&pcp->lock); In this case, after calling zone_pcp_disable() though, there are still some pages in pcp_list. And these pages in pcp_list are neither movable nor isolated, offline_pages() gets stuck as a result. Solution: Expand the scope of the pcp->lock to also protect pcp->count in drain_pages_zone(), to ensure no pages are left in the pcp list after zone_pcp_disable() [1] https://lore.kernel.org/linux-mm/6a07125f-e720-404c-b2f9-e55f3f166e85@fujitsu.com/ Cc: David Hildenbrand <david@redhat.com> Cc: Vlastimil Babka (SUSE) <vbabka@kernel.org> Reported-by: Yao Xingtao <yaoxt.fnst@fujitsu.com> Signed-off-by: Li Zhijian <lizhijian@fujitsu.com> --- V3: Read pcp->count in the loop with lock held to prevent unnecessary spin_lock() wasteful V2: - Narrow down the scope of the spin_lock() to limit the draining latency. # Vlastimil and David - In above scenario, it's sufficient to read pcp->count once with lock held, and it fully fixed my issue[1] in thounds runs(It happened in more than 5% before). RFC: https://lore.kernel.org/linux-mm/20240716073929.843277-1-lizhijian@fujitsu.com/ Signed-off-by: Li Zhijian <lizhijian@fujitsu.com> --- mm/page_alloc.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-)