| Message ID | 20220824071909.192535-1-wangkefeng.wang@huawei.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] mm: fix null-ptr-deref in kswapd_is_running() | expand |
On 24.08.22 09:19, Kefeng Wang 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() > if (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 race between kswapd_run() and kcompactd(), adding a temporary value > when create a kthread, and only set it to pgdat->kswapd if kthread_run() > return successful task_struct to fix the issue. > > For race between kswapd_stop() and kcompactd(), let's call kcompactd_stop() > before kswapd_stop() to fix the issue. > > Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com> > --- > mm/memory_hotplug.c | 2 +- > mm/vmscan.c | 8 +++++--- > 2 files changed, 6 insertions(+), 4 deletions(-) > > 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); > } This looks just fragile to randomly break again in the future when people work on this code without being aware of this condition. Or once with other (future?) kswapd_is_running() users. We at least need some comment explaining that the order here matters and why. But I do wonder if we can't handle it in a cleaner, more obvious, way. kswapd_start()/kswapd_stop() should have a proper way to synchronize with kswapd_is_running(). Just the matter of finding a suitable locking primitive :)
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/vmscan.c b/mm/vmscan.c index b2b1431352dc..08c6497f76c3 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -4642,16 +4642,18 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim) void kswapd_run(int nid) { pg_data_t *pgdat = NODE_DATA(nid); + struct task_struct *t; if (pgdat->kswapd) return; - pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid); - if (IS_ERR(pgdat->kswapd)) { + t = kthread_run(kswapd, pgdat, "kswapd%d", nid); + if (IS_ERR(t)) { /* 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; + } else { + pgdat->kswapd = t; } }
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() if (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 race between kswapd_run() and kcompactd(), adding a temporary value when create a kthread, and only set it to pgdat->kswapd if kthread_run() return successful task_struct to fix the issue. For race between kswapd_stop() and kcompactd(), let's call kcompactd_stop() before kswapd_stop() to fix the issue. Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com> --- mm/memory_hotplug.c | 2 +- mm/vmscan.c | 8 +++++--- 2 files changed, 6 insertions(+), 4 deletions(-)