Messages in this thread Patch in this message | | | From | Xuewen Yan <> | Date | Fri, 29 Jul 2022 15:33:22 +0800 | Subject | Re: [PATCH] sched/schedutil: Fix deadlock between cpuset and cpu hotplug when using schedutil |
| |
Hi Tejun
On Thu, Jul 28, 2022 at 4:09 AM Tejun Heo <tj@kernel.org> wrote: > > Hello, > > > Can youp please see whether the following patch fixes the problem? >
I have tested the patch, sadly, although the original deadlock call stack is gone, there seems to be a new problem. I did a preliminary analysis, but no further in-depth analysis. I haven't found the root cause yet, but I think I should let you know the test results first. Once I find the root cause, I'll report back immediately. The thread-A is waiting for the cpu_hotplug_lock's writer, but the writer is waiting for the readers:
PID: 1106 TASK: ffffff8097e90000 CPU: 7 COMMAND: "OomAdjuster" #0 [ffffffc011a23850] __switch_to at ffffffc0081229b4 #1 [ffffffc011a238b0] __schedule at ffffffc009c824f8 #2 [ffffffc011a23910] schedule at ffffffc009c82b50 #3 [ffffffc011a23970] percpu_rwsem_wait at ffffffc00828fbf4 #4 [ffffffc011a239b0] __percpu_down_read at ffffffc0082901a8 #5 [ffffffc011a239e0] cpus_read_lock at ffffffc0081dadc8 #6 [ffffffc011a23a20] cpuset_attach at ffffffc008366f10 #7 [ffffffc011a23a90] cgroup_migrate_execute at ffffffc00834f808 #8 [ffffffc011a23b60] cgroup_attach_task at ffffffc0083539f0 #9 [ffffffc011a23bd0] __cgroup1_procs_write at ffffffc00835f6e8 #10 [ffffffc011a23c30] cgroup1_tasks_write at ffffffc00835f054 #11 [ffffffc011a23c60] cgroup_file_write at ffffffc008348b2c #12 [ffffffc011a23c90] kernfs_fop_write_iter at ffffffc008754514 #13 [ffffffc011a23d50] vfs_write at ffffffc008607ac8 #14 [ffffffc011a23db0] ksys_write at ffffffc008607714 #15 [ffffffc011a23df0] __arm64_sys_write at ffffffc00860767c #16 [ffffffc011a23e10] invoke_syscall at ffffffc00813dcac #17 [ffffffc011a23e30] el0_svc_common at ffffffc00813dbc4 #18 [ffffffc011a23e70] do_el0_svc at ffffffc00813daa8 #19 [ffffffc011a23e80] el0_svc at ffffffc0098828d8 #20 [ffffffc011a23ea0] el0t_64_sync_handler at ffffffc00988284c #21 [ffffffc011a23fe0] el0t_64_sync at ffffffc008091e44
cpu_hotplug_lock = $3 = { rss = { gp_state = 2, gp_count = 1, gp_wait = { lock = { { rlock = { raw_lock = { { val = { counter = 0 }, { locked = 0 '\000', pending = 0 '\000' }, { locked_pending = 0, tail = 0 } } } } } }, head = { next = 0xffffffc00b0eb6a0 <cpu_hotplug_lock+16>, prev = 0xffffffc00b0eb6a0 <cpu_hotplug_lock+16> } }, cb_head = { next = 0x0, func = 0x0 } }, read_count = 0xffffffc00b0a0808 <__percpu_rwsem_rc_cpu_hotplug_lock>, writer = { task = 0xffffff80f303ca00 }, { waiters = { lock = { { rlock = { raw_lock = { { val = { counter = 0 }, { locked = 0 '\000', pending = 0 '\000' }, { locked_pending = 0, tail = 0 } } } } } }, head = { next = 0xffffffc011a23958, prev = 0xffffffc01430bcb8 } }, destroy_list_entry = { next = 0x0, prev = 0xffffffc011a23958 } }, block = { counter = 1 } }
PID: 15760 TASK: ffffff80f303ca00 CPU: 5 COMMAND: "test.sh" #0 [ffffffc0129639a0] __switch_to at ffffffc0081229b4 #1 [ffffffc012963a00] __schedule at ffffffc009c824f8 #2 [ffffffc012963a60] schedule at ffffffc009c82b50 #3 [ffffffc012963a90] percpu_down_write at ffffffc00828f9d8 #4 [ffffffc012963ae0] _cpu_down at ffffffc009884550 #5 [ffffffc012963b40] cpu_device_down at ffffffc0081df814 #6 [ffffffc012963b60] cpu_subsys_offline at ffffffc008d8dd8c #7 [ffffffc012963b90] device_offline at ffffffc008d77124 #8 [ffffffc012963bd0] online_store at ffffffc008d76d44 #9 [ffffffc012963c30] dev_attr_store at ffffffc008d7ba30 #10 [ffffffc012963c60] sysfs_kf_write at ffffffc0087578d0 #11 [ffffffc012963c90] kernfs_fop_write_iter at ffffffc008754514 #12 [ffffffc012963d50] vfs_write at ffffffc008607ac8 #13 [ffffffc012963db0] ksys_write at ffffffc008607714 #14 [ffffffc012963df0] __arm64_sys_write at ffffffc00860767c #15 [ffffffc012963e10] invoke_syscall at ffffffc00813dcac #16 [ffffffc012963e30] el0_svc_common at ffffffc00813dbf4 #17 [ffffffc012963e70] do_el0_svc at ffffffc00813daa8 #18 [ffffffc012963e80] el0_svc at ffffffc0098828d8 #19 [ffffffc012963ea0] el0t_64_sync_handler at ffffffc00988284c #20 [ffffffc012963fe0] el0t_64_sync at ffffffc008091e44
Thanks! BR -- xuewen.yan
> Thanks. > > diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c > index 13c8e91d78620..7caefc8af9127 100644 > --- a/kernel/cgroup/cgroup.c > +++ b/kernel/cgroup/cgroup.c > @@ -2345,6 +2345,38 @@ int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen) > } > EXPORT_SYMBOL_GPL(task_cgroup_path); > > +/** > + * lock_threadgroup - Stabilize threadgroups > + * > + * cgroup migration operations need the threadgroups stabilized against forks > + * and exits, which can be achieved by write-locking cgroup_threadgroup_rwsem. > + * > + * Note that write-locking threadgdroup_rwsem is nested inside CPU hotplug > + * disable. This is because cpuset needs CPU hotplug disabled during ->attach() > + * and bringing up a CPU may involve creating new tasks which can require > + * read-locking threadgroup_rwsem. If we call cpuset's ->attach() with > + * threadgroup_rwsem write-locked with hotplug enabled, we can deadlock by > + * cpuset waiting for an on-going CPU hotplug operation which in turn is waiting > + * for the threadgroup_rwsem to be released to create new tasks. See the > + * following for more details: > + * > + * http://lkml.kernel.org/r/20220711174629.uehfmqegcwn2lqzu@wubuntu > + */ > +static void lock_threadgroup(void) > +{ > + cpus_read_lock(); > + percpu_down_write(&cgroup_threadgroup_rwsem); > +} > + > +/** > + * lock_threadgroup - Undo lock_threadgroup > + */ > +static void unlock_threadgroup(void) > +{ > + percpu_up_write(&cgroup_threadgroup_rwsem); > + cpus_read_unlock(); > +} > + > /** > * cgroup_migrate_add_task - add a migration target task to a migration context > * @task: target task > @@ -2822,7 +2854,6 @@ int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader, > > struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup, > bool *locked) > - __acquires(&cgroup_threadgroup_rwsem) > { > struct task_struct *tsk; > pid_t pid; > @@ -2840,7 +2871,7 @@ struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup, > */ > lockdep_assert_held(&cgroup_mutex); > if (pid || threadgroup) { > - percpu_down_write(&cgroup_threadgroup_rwsem); > + lock_threadgroup(); > *locked = true; > } else { > *locked = false; > @@ -2876,7 +2907,7 @@ struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup, > > out_unlock_threadgroup: > if (*locked) { > - percpu_up_write(&cgroup_threadgroup_rwsem); > + unlock_threadgroup(); > *locked = false; > } > out_unlock_rcu: > @@ -2885,7 +2916,6 @@ struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup, > } > > void cgroup_procs_write_finish(struct task_struct *task, bool locked) > - __releases(&cgroup_threadgroup_rwsem) > { > struct cgroup_subsys *ss; > int ssid; > @@ -2894,7 +2924,8 @@ void cgroup_procs_write_finish(struct task_struct *task, bool locked) > put_task_struct(task); > > if (locked) > - percpu_up_write(&cgroup_threadgroup_rwsem); > + unlock_threadgroup(); > + > for_each_subsys(ss, ssid) > if (ss->post_attach) > ss->post_attach(); > @@ -2953,7 +2984,7 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp) > > lockdep_assert_held(&cgroup_mutex); > > - percpu_down_write(&cgroup_threadgroup_rwsem); > + lock_threadgroup(); > > /* look up all csses currently attached to @cgrp's subtree */ > spin_lock_irq(&css_set_lock); > @@ -2984,7 +3015,7 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp) > ret = cgroup_migrate_execute(&mgctx); > out_finish: > cgroup_migrate_finish(&mgctx); > - percpu_up_write(&cgroup_threadgroup_rwsem); > + unlock_threadgroup(); > return ret; > } >
| |