Hello, BPF developers. Alexey Kardashevskiy is reporting that system_wq gets stuck due to flooding of unbounded bpf_map_free_deferred work. Use of WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_UNBOUND workqueue did not solve this problem. Is it possible that a refcount leak somewhere preventing bpf_map_free_deferred from completing? Please see https://lkml.kernel.org/r/CACT4Y+Z+kwPM=WUzJ-e359PWeLLqmF0w4Yxp1spzZ=+J0ekrag@xxxxxxxxxxxxxx . On 2021/01/23 7:53, Alexey Kardashevskiy wrote: > > > On 23/01/2021 02:30, Tetsuo Handa wrote: >> On 2021/01/22 22:28, Tetsuo Handa wrote: >>> On 2021/01/22 21:10, Dmitry Vyukov wrote: >>>> On Fri, Jan 22, 2021 at 1:03 PM Alexey Kardashevskiy <aik@xxxxxxxxx> wrote: >>>>> >>>>> >>>>> >>>>> On 22/01/2021 21:30, Tetsuo Handa wrote: >>>>>> On 2021/01/22 18:16, Dmitry Vyukov wrote: >>>>>>> The reproducer only does 2 bpf syscalls, so something is slowly leaking in bpf. >>>>>>> My first suspect would be one of these. Since workqueue is async, it >>>>>>> may cause such slow drain that happens only when tasks are spawned >>>>>>> fast. I don't know if there is a procfs/debugfs introspection file to >>>>>>> monitor workqueue lengths to verify this hypothesis. >>>>>> >>>>>> If you can reproduce locally, you can call show_workqueue_state() >>>>>> (part of SysRq-t) when hitting the limit. >>>>>> >>>>>> --- a/kernel/locking/lockdep.c >>>>>> +++ b/kernel/locking/lockdep.c >>>>>> @@ -1277,6 +1277,7 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force) >>>>>> >>>>>> print_lockdep_off("BUG: MAX_LOCKDEP_KEYS too low!"); >>>>>> dump_stack(); >>>>>> + show_workqueue_state(); >>>>>> return NULL; >>>>>> } >>>>>> nr_lock_classes++; >>>>>> >>>>> >>>>> >>>>> >>>>> Here is the result: >>>>> https://pastebin.com/rPn0Cytu >>>> >>>> Do you mind posting this publicly? >>>> Yes, it seems that bpf_map_free_deferred is the problem (11138 >>>> outstanding callbacks). >>>> >>> >>> Wow. Horribly stuck queue. I guess BPF wants to try WQ created by >>> >>> alloc_workqueue("bpf_free_wq", WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_UNBOUND, 0); >>> >>> rather than system_wq . You can add Tejun Heo <tj@xxxxxxxxxx> for WQ. >>> >>> Anyway, please post your result to ML. > > > > https://pastebin.com/JfrmzguK is with the patch below applied. Seems less output. Interestingly when I almost hit "send", OOM kicked in and tried killing a bunch of "maxlockdep" processes (my test case): > > [ 891.037315] [ 31007] 0 31007 281 5 49152 0 1000 maxlockdep > [ 891.037540] [ 31009] 0 31009 281 5 49152 0 1000 maxlockdep > [ 891.037760] [ 31012] 0 31012 281 5 49152 0 1000 maxlockdep > [ 891.037980] [ 31013] 0 31013 281 5 47104 0 0 maxlockdep > [ 891.038210] [ 31014] 0 31014 281 5 49152 0 1000 maxlockdep > [ 891.038429] [ 31018] 0 31018 281 5 47104 0 0 maxlockdep > [ 891.038652] [ 31019] 0 31019 281 5 49152 0 1000 maxlockdep > [ 891.038874] [ 31020] 0 31020 281 5 49152 0 1000 maxlockdep > [ 891.039095] [ 31021] 0 31021 281 5 49152 0 1000 maxlockdep > [ 891.039317] [ 31022] 0 31022 281 5 47104 0 0 maxlockdep > > > > > And (re)adding LKML and Tejun as suggested. Thanks, > > >>> >> >> Does this patch (which is only compile tested) reduce number of pending works >> when hitting "BUG: MAX_LOCKDEP_KEYS too low!" ? >> >> diff --git a/include/linux/bpf.h b/include/linux/bpf.h >> index 07cb5d15e743..c6c6902090f0 100644 >> --- a/include/linux/bpf.h >> +++ b/include/linux/bpf.h >> @@ -41,6 +41,7 @@ struct bpf_local_storage_map; >> struct kobject; >> struct mem_cgroup; >> +extern struct workqueue_struct *bpf_free_wq; >> extern struct idr btf_idr; >> extern spinlock_t btf_idr_lock; >> extern struct kobject *btf_kobj; >> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c >> index 1f8453343bf2..8b1cf6aab089 100644 >> --- a/kernel/bpf/arraymap.c >> +++ b/kernel/bpf/arraymap.c >> @@ -994,7 +994,7 @@ static void prog_array_map_clear(struct bpf_map *map) >> struct bpf_array_aux *aux = container_of(map, struct bpf_array, >> map)->aux; >> bpf_map_inc(map); >> - schedule_work(&aux->work); >> + queue_work(bpf_free_wq, &aux->work); >> } >> static struct bpf_map *prog_array_map_alloc(union bpf_attr *attr) >> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c >> index 96555a8a2c54..f272844163df 100644 >> --- a/kernel/bpf/cgroup.c >> +++ b/kernel/bpf/cgroup.c >> @@ -160,7 +160,7 @@ static void cgroup_bpf_release_fn(struct percpu_ref *ref) >> struct cgroup *cgrp = container_of(ref, struct cgroup, bpf.refcnt); >> INIT_WORK(&cgrp->bpf.release_work, cgroup_bpf_release); >> - queue_work(system_wq, &cgrp->bpf.release_work); >> + queue_work(bpf_free_wq, &cgrp->bpf.release_work); >> } >> /* Get underlying bpf_prog of bpf_prog_list entry, regardless if it's through >> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c >> index 261f8692d0d2..9d76c0d77687 100644 >> --- a/kernel/bpf/core.c >> +++ b/kernel/bpf/core.c >> @@ -34,6 +34,15 @@ >> #include <linux/log2.h> >> #include <asm/unaligned.h> >> +struct workqueue_struct *bpf_free_wq; >> + >> +static int __init bpf_free_wq_init(void) >> +{ >> + bpf_free_wq = alloc_workqueue("bpf_free_wq", WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_UNBOUND, 0); >> + return 0; >> +} >> +subsys_initcall(bpf_free_wq_init); >> + >> /* Registers */ >> #define BPF_R0 regs[BPF_REG_0] >> #define BPF_R1 regs[BPF_REG_1] >> @@ -2152,7 +2161,7 @@ void bpf_prog_free(struct bpf_prog *fp) >> if (aux->dst_prog) >> bpf_prog_put(aux->dst_prog); >> INIT_WORK(&aux->work, bpf_prog_free_deferred); >> - schedule_work(&aux->work); >> + queue_work(bpf_free_wq, &aux->work); >> } >> EXPORT_SYMBOL_GPL(bpf_prog_free); >> diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c >> index 747313698178..6507cc8263fc 100644 >> --- a/kernel/bpf/cpumap.c >> +++ b/kernel/bpf/cpumap.c >> @@ -515,7 +515,7 @@ static void __cpu_map_entry_replace(struct bpf_cpu_map *cmap, >> if (old_rcpu) { >> call_rcu(&old_rcpu->rcu, __cpu_map_entry_free); >> INIT_WORK(&old_rcpu->kthread_stop_wq, cpu_map_kthread_stop); >> - schedule_work(&old_rcpu->kthread_stop_wq); >> + queue_work(bpf_free_wq, &old_rcpu->kthread_stop_wq); >> } >> } >> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c >> index e5999d86c76e..084b903b4ee6 100644 >> --- a/kernel/bpf/syscall.c >> +++ b/kernel/bpf/syscall.c >> @@ -477,7 +477,7 @@ static void __bpf_map_put(struct bpf_map *map, bool do_idr_lock) >> bpf_map_free_id(map, do_idr_lock); >> btf_put(map->btf); >> INIT_WORK(&map->work, bpf_map_free_deferred); >> - schedule_work(&map->work); >> + queue_work(bpf_free_wq, &map->work); >> } >> } >> @@ -2343,7 +2343,7 @@ void bpf_link_put(struct bpf_link *link) >> if (in_atomic()) { >> INIT_WORK(&link->work, bpf_link_put_deferred); >> - schedule_work(&link->work); >> + queue_work(bpf_free_wq, &link->work); >> } else { >> bpf_link_free(link); >> } >> >
