The kswapd_run/stop() will set pgdat->kswapd to NULL, which
could race with kswapd_is_running() in kcompactd(),
kswapd_run/stop() kcompactd()
kswapd_is_running()
pgdat->kswapd // error or nomal ptr
verify pgdat->kswapd
// load non-NULL
pgdat->kswapd
pgdat->kswapd = NULL
task_is_running(pgdat->kswapd)
// Null pointer derefence
The KASAN report the null-ptr-deref shown below,
vmscan: Failed to start kswapd on node 0
...
BUG: KASAN: null-ptr-deref in kcompactd+0x440/0x504
Read of size 8 at addr 0000000000000024 by task kcompactd0/37
CPU: 0 PID: 37 Comm: kcompactd0 Kdump: loaded Tainted: G OE 5.10.60 #1
Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
Call trace:
dump_backtrace+0x0/0x394
show_stack+0x34/0x4c
dump_stack+0x158/0x1e4
__kasan_report+0x138/0x140
kasan_report+0x44/0xdc
__asan_load8+0x94/0xd0
kcompactd+0x440/0x504
kthread+0x1a4/0x1f0
ret_from_fork+0x10/0x18
For now, kswapd/kcompactd_run() and kswapd/kcompactd_stop() protected
by mem_hotplug_begin/done(), but without kcompactd(). It is no need to
involve memory hotplug lock in kcompactd(), so let's add new mutex to
protect pgdat->kswapd accessed concurrently, also because kcompactd task
will check the state of kswapd task, it's better to call kcompactd_stop()
before kswapd_stop() to reduce lock conflicts.
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
---
v2: add new lock to protect pgdat->kswapd, suggested by David Hildenbrand
include/linux/memory_hotplug.h | 19 +++++++++++++++++++
include/linux/mmzone.h | 6 ++++--
mm/compaction.c | 8 +++++++-
mm/memory_hotplug.c | 2 +-
mm/page_alloc.c | 1 +
mm/vmscan.c | 27 ++++++++++++++++-----------
6 files changed, 48 insertions(+), 15 deletions(-)
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index e0b2209ab71c..409196ef8038 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -216,6 +216,21 @@ void put_online_mems(void);
void mem_hotplug_begin(void);
void mem_hotplug_done(void);
+static inline void pgdat_kswapd_lock(pg_data_t *pgdat)
+{
+ mutex_lock(&pgdat->kswapd_lock);
+}
+
+static inline void pgdat_kswapd_unlock(pg_data_t *pgdat)
+{
+ mutex_unlock(&pgdat->kswapd_lock);
+}
+
+static inline void pgdat_kswapd_lock_init(pg_data_t *pgdat)
+{
+ mutex_init(&pgdat->kswapd_lock);
+}
+
#else /* ! CONFIG_MEMORY_HOTPLUG */
#define pfn_to_online_page(pfn) \
({ \
@@ -252,6 +267,10 @@ static inline bool movable_node_is_enabled(void)
{
return false;
}
+
+static inline void pgdat_kswapd_lock(pg_data_t *pgdat) {}
+static inline void pgdat_kswapd_unlock(pg_data_t *pgdat) {}
+static inline void pgdat_kswapd_lock_init(pg_data_t *pgdat) {}
#endif /* ! CONFIG_MEMORY_HOTPLUG */
/*
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 14919b2fb5f5..9e2317659520 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1165,8 +1165,10 @@ typedef struct pglist_data {
atomic_t nr_writeback_throttled;/* nr of writeback-throttled tasks */
unsigned long nr_reclaim_start; /* nr pages written while throttled
* when throttling started. */
- struct task_struct *kswapd; /* Protected by
- mem_hotplug_begin/done() */
+#ifdef CONFIG_MEMORY_HOTPLUG
+ struct mutex kswapd_lock;
+#endif
+ struct task_struct *kswapd; /* Protected by kswapd_lock */
int kswapd_order;
enum zone_type kswapd_highest_zoneidx;
diff --git a/mm/compaction.c b/mm/compaction.c
index eb2de3c06ce0..6e9dd600ba4e 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1982,7 +1982,13 @@ 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);
+ bool running;
+
+ pgdat_kswapd_lock(pgdat);
+ running = pgdat->kswapd && task_is_running(pgdat->kswapd);
+ pgdat_kswapd_unlock(pgdat);
+
+ return running;
}
/*
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index fad6d1f2262a..2fd45ccbce45 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1940,8 +1940,8 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
node_states_clear_node(node, &arg);
if (arg.status_change_nid >= 0) {
- kswapd_stop(node);
kcompactd_stop(node);
+ kswapd_stop(node);
}
writeback_set_ratelimit();
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 045543fa310e..4e91b1753f00 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7619,6 +7619,7 @@ static void __meminit pgdat_init_internals(struct pglist_data *pgdat)
int i;
pgdat_resize_init(pgdat);
+ pgdat_kswapd_lock_init(pgdat);
pgdat_init_split_queue(pgdat);
pgdat_init_kcompactd(pgdat);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 27a3f29c0181..f30ab03df2ba 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -7425,16 +7425,17 @@ void kswapd_run(int nid)
{
pg_data_t *pgdat = NODE_DATA(nid);
- if (pgdat->kswapd)
- return;
-
- pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
- if (IS_ERR(pgdat->kswapd)) {
- /* failure at boot is fatal */
- BUG_ON(system_state < SYSTEM_RUNNING);
- pr_err("Failed to start kswapd on node %d\n", nid);
- pgdat->kswapd = NULL;
+ pgdat_kswapd_lock(pgdat);
+ if (!pgdat->kswapd) {
+ pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
+ if (IS_ERR(pgdat->kswapd)) {
+ /* failure at boot is fatal */
+ BUG_ON(system_state < SYSTEM_RUNNING);
+ pr_err("Failed to start kswapd on node %d\n", nid);
+ pgdat->kswapd = NULL;
+ }
}
+ pgdat_kswapd_unlock(pgdat);
}
/*
@@ -7443,12 +7444,16 @@ void kswapd_run(int nid)
*/
void kswapd_stop(int nid)
{
- struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
+ pg_data_t *pgdat = NODE_DATA(nid);
+ struct task_struct *kswapd;
+ pgdat_kswapd_lock(pgdat);
+ kswapd = pgdat->kswapd;
if (kswapd) {
kthread_stop(kswapd);
- NODE_DATA(nid)->kswapd = NULL;
+ pgdat->kswapd = NULL;
}
+ pgdat_kswapd_unlock(pgdat);
}
static int __init kswapd_init(void)
--
2.35.3
