From b4a0215e11dcfe23a48c65c6d6c82c0c2c551a48 Mon Sep 17 00:00:00 2001 From: Kefeng Wang Date: Sat, 27 Aug 2022 19:19:59 +0800 Subject: 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: Kefeng Wang Cc: David Hildenbrand Cc: Muchun Song Signed-off-by: Andrew Morton --- include/linux/memory_hotplug.h | 20 ++++++++++++++++++++ include/linux/mmzone.h | 6 ++++-- 2 files changed, 24 insertions(+), 2 deletions(-) (limited to 'include/linux') diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h index 54675791bc50..51052969dbfe 100644 --- a/include/linux/memory_hotplug.h +++ b/include/linux/memory_hotplug.h @@ -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 */ /* diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index fd61347b4b1f..18cf0fc5ce67 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -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; -- cgit v1.2.3-59-g8ed1b