Commit b4a0215e authored by Kefeng Wang's avatar Kefeng Wang Committed by Andrew Morton
Browse files

mm: fix null-ptr-deref in kswapd_is_running() 

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

KASAN reports 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

At present kswapd/kcompactd_run() and kswapd/kcompactd_stop() are protected
by mem_hotplug_begin/done(), but without kcompactd(). There is no need to
involve memory hotplug lock in kcompactd(), so let's add a new mutex to
protect pgdat->kswapd accesses.

Also, because the kcompactd task will check the state of kswapd task, it's
better to call kcompactd_stop() before kswapd_stop() to reduce lock
conflicts.

[akpm@linux-foundation.org: add comments]
Link: https://lkml.kernel.org/r/20220827111959.186838-1-wangkefeng.wang@huawei.com


Signed-off-by: default avatarKefeng Wang <wangkefeng.wang@huawei.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 639118d1

include/linux/memory_hotplug.h

+20 −0
Original line number Diff line number Diff line
@@ -215,6 +215,22 @@ void put_online_mems(void); 
void mem_hotplug_begin(void);

void mem_hotplug_done(void);



/* See kswapd_is_running() */

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)			\

({						\
@@ -251,6 +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 */



/*

include/linux/mmzone.h

+4 −2
Original line number Diff line number Diff line
@@ -956,8 +956,10 @@ 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;

mm/compaction.c

+13 −1
Original line number Diff line number Diff line
@@ -1981,9 +1981,21 @@ static inline bool is_via_compact_memory(int order) 
	return order == -1;

}



/*

 * Determine whether kswapd is (or recently was!) running on this node.

 *

 * pgdat_kswapd_lock() pins pgdat->kswapd, so a concurrent kswapd_stop() can't

 * zero it.

 */

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;

}



/*

mm/memory_hotplug.c

+1 −1
Original line number Diff line number Diff line
@@ -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();

mm/page_alloc.c

+1 −0
Original line number Diff line number Diff line
@@ -7616,6 +7616,7 @@ 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);