hulk inclusion category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/IA4VMT

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We found an AA deadlock problem as shown belowed:

cgroup_destroy_wq TaskB WatchDog system_wq

... css_killed_work_fn: P(cgroup_mutex) ... ... __lockup_detector_reconfigure: P(cpu_hotplug_lock.read) ... ... percpu_down_write: P(cpu_hotplug_lock.write) ... cgroup_bpf_release: P(cgroup_mutex) smp_call_on_cpu: Wait system_wq

cpuset_css_offline: P(cpu_hotplug_lock.read)

WatchDog is waiting for system_wq, who is waiting for cgroup_mutex, to finish the jobs, but the owner of the cgroup_mutex is waiting for cpu_hotplug_lock. This problem caused by commit 4bfc0bb2c60e ("bpf: decouple the lifetime of cgroup_bpf from cgroup itself") puts cgroup_bpf release work into system_wq. As cgroup_bpf is a member of cgroup, it is reasonable to put cgroup bpf release work into cgroup_destroy_wq, which is only used for cgroup's release work, and the problem is solved.

Fixes: 4bfc0bb2c60e ("bpf: decouple the lifetime of cgroup_bpf from cgroup itself") Signed-off-by: Chen Ridong chenridong@huawei.com --- kernel/bpf/cgroup.c | 2 +- kernel/cgroup/cgroup-internal.h | 1 + kernel/cgroup/cgroup.c | 2 +- 3 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c index ac37bd53aee0..a511fdc623d2 100644 --- a/kernel/bpf/cgroup.c +++ b/kernel/bpf/cgroup.c @@ -334,7 +334,7 @@ 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(cgroup_destroy_wq, &cgrp->bpf.release_work); }

/* Get underlying bpf_prog of bpf_prog_list entry, regardless if it's through diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h index f5fb12890645..21be00b7241f 100644 --- a/kernel/cgroup/cgroup-internal.h +++ b/kernel/cgroup/cgroup-internal.h @@ -13,6 +13,7 @@ extern spinlock_t trace_cgroup_path_lock; extern char trace_cgroup_path[TRACE_CGROUP_PATH_LEN]; extern void __init enable_debug_cgroup(void); +extern struct workqueue_struct *cgroup_destroy_wq;

/* * cgroup_path() takes a spin lock. It is good practice not to take diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 0a64ad82cb9b..47fb0c00b512 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -126,7 +126,7 @@ DEFINE_PERCPU_RWSEM(cgroup_threadgroup_rwsem); * destruction work items don't end up filling up max_active of system_wq * which may lead to deadlock. */ -static struct workqueue_struct *cgroup_destroy_wq; +struct workqueue_struct *cgroup_destroy_wq;

/* generate an array of cgroup subsystem pointers */ #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys,