mm, memory_hotplug: get rid of zonelists_mutex

zonelists_mutex was introduced by commit 4eaf3f64397c ("mem-hotplug: fix
potential race while building zonelist for new populated zone") to
protect zonelist building from races.  This is no longer needed though
because both memory online and offline are fully serialized.  New users
have grown since then.

Notably setup_per_zone_wmarks wants to prevent from races between memory
hotplug, khugepaged setup and manual min_free_kbytes update via sysctl
(see cfd3da1e49bb ("mm: Serialize access to min_free_kbytes").  Let's
add a private lock for that purpose.  This will not prevent from seeing
halfway through memory hotplug operation but that shouldn't be a big
deal becuse memory hotplug will update watermarks explicitly so we will
eventually get a full picture.  The lock just makes sure we won't race
when updating watermarks leading to weird results.

Also __build_all_zonelists manipulates global data so add a private lock
for it as well.  This doesn't seem to be necessary today but it is more
robust to have a lock there.

While we are at it make sure we document that memory online/offline
depends on a full serialization either via mem_hotplug_begin() or
device_lock.

Link: http://lkml.kernel.org/r/20170721143915.14161-9-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Shaohua Li <shaohua.li@intel.com>
Cc: Toshi Kani <toshi.kani@hpe.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Haicheng Li <haicheng.li@linux.intel.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 9 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e3086d0fd945..0bea94af0423 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5131,17 +5131,14 @@ static void setup_pageset(struct per_cpu_pageset *p, unsigned long batch);
 static DEFINE_PER_CPU(struct per_cpu_pageset, boot_pageset);
 static DEFINE_PER_CPU(struct per_cpu_nodestat, boot_nodestats);
 
-/*
- * Global mutex to protect against size modification of zonelists
- * as well as to serialize pageset setup for the new populated zone.
- */
-DEFINE_MUTEX(zonelists_mutex);
-
 static void __build_all_zonelists(void *data)
 {
 	int nid;
 	int __maybe_unused cpu;
 	pg_data_t *self = data;
+	static DEFINE_SPINLOCK(lock);
+
+	spin_lock(&lock);
 
 #ifdef CONFIG_NUMA
 	memset(node_load, 0, sizeof(node_load));
@@ -5173,6 +5170,8 @@ static void __build_all_zonelists(void *data)
 			set_cpu_numa_mem(cpu, local_memory_node(cpu_to_node(cpu)));
 #endif
 	}
+
+	spin_unlock(&lock);
 }
 
 static noinline void __init
@@ -5203,7 +5202,6 @@ build_all_zonelists_init(void)
 }
 
 /*
- * Called with zonelists_mutex held always
  * unless system_state == SYSTEM_BOOTING.
  *
  * __ref due to call of __init annotated helper build_all_zonelists_init
@@ -6939,9 +6937,11 @@ static void __setup_per_zone_wmarks(void)
  */
 void setup_per_zone_wmarks(void)
 {
-	mutex_lock(&zonelists_mutex);
+	static DEFINE_SPINLOCK(lock);
+
+	spin_lock(&lock);
 	__setup_per_zone_wmarks();
-	mutex_unlock(&zonelists_mutex);
+	spin_unlock(&lock);
 }
 
 /*