| Message ID | 20220827111959.186838-1-wangkefeng.wang@huawei.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] mm: fix null-ptr-deref in kswapd_is_running() | expand |
On Sat, 27 Aug 2022 19:19:59 +0800 Kefeng Wang <wangkefeng.wang@huawei.com> wrote: > 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. > Looks right to me. I think the below will make the code a little more maintainable? --- a/include/linux/memory_hotplug.h~mm-fix-null-ptr-deref-in-kswapd_is_running-fix +++ a/include/linux/memory_hotplug.h @@ -215,6 +215,7 @@ 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); --- a/mm/compaction.c~mm-fix-null-ptr-deref-in-kswapd_is_running-fix +++ a/mm/compaction.c @@ -1980,6 +1980,12 @@ static inline bool is_via_compact_memory 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) { bool running;
On 2022/8/28 6:08, Andrew Morton wrote: > On Sat, 27 Aug 2022 19:19:59 +0800 Kefeng Wang <wangkefeng.wang@huawei.com> wrote: > >> 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. >> > Looks right to me. > > I think the below will make the code a little more maintainable? Thanks Andrew, it's better. > > --- a/include/linux/memory_hotplug.h~mm-fix-null-ptr-deref-in-kswapd_is_running-fix > +++ a/include/linux/memory_hotplug.h > @@ -215,6 +215,7 @@ 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); > --- a/mm/compaction.c~mm-fix-null-ptr-deref-in-kswapd_is_running-fix > +++ a/mm/compaction.c > @@ -1980,6 +1980,12 @@ static inline bool is_via_compact_memory > 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) > { > bool running; > _ > > .
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)
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@redhat.com> Cc: Muchun Song <muchun.song@linux.dev> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com> --- 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(-)