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SubjectRe: [PATCH v8 2/6] cpuset: Add new v2 cpuset.sched.domain flag
Hi,

On 17/05/18 16:55, Waiman Long wrote:

[...]

> /**
> + * update_isolated_cpumask - update the isolated_cpus mask of parent cpuset
> + * @cpuset: The cpuset that requests CPU isolation
> + * @oldmask: The old isolated cpumask to be removed from the parent
> + * @newmask: The new isolated cpumask to be added to the parent
> + * Return: 0 if successful, an error code otherwise
> + *
> + * Changes to the isolated CPUs are not allowed if any of CPUs changing
> + * state are in any of the child cpusets of the parent except the requesting
> + * child.
> + *
> + * If the sched_domain flag changes, either the oldmask (0=>1) or the
> + * newmask (1=>0) will be NULL.
> + *
> + * Called with cpuset_mutex held.
> + */
> +static int update_isolated_cpumask(struct cpuset *cpuset,
> + struct cpumask *oldmask, struct cpumask *newmask)
> +{
> + int retval;
> + int adding, deleting;
> + cpumask_var_t addmask, delmask;
> + struct cpuset *parent = parent_cs(cpuset);
> + struct cpuset *sibling;
> + struct cgroup_subsys_state *pos_css;
> + int old_count = parent->isolation_count;
> + bool dying = cpuset->css.flags & CSS_DYING;
> +
> + /*
> + * Parent must be a scheduling domain with non-empty cpus_allowed.
> + */
> + if (!is_sched_domain(parent) || cpumask_empty(parent->cpus_allowed))
> + return -EINVAL;
> +
> + /*
> + * The oldmask, if present, must be a subset of parent's isolated
> + * CPUs.
> + */
> + if (oldmask && !cpumask_empty(oldmask) && (!parent->isolation_count ||
> + !cpumask_subset(oldmask, parent->isolated_cpus))) {
> + WARN_ON_ONCE(1);
> + return -EINVAL;
> + }
> +
> + /*
> + * A sched_domain state change is not allowed if there are
> + * online children and the cpuset is not dying.
> + */
> + if (!dying && (!oldmask || !newmask) &&
> + css_has_online_children(&cpuset->css))
> + return -EBUSY;
> +
> + if (!zalloc_cpumask_var(&addmask, GFP_KERNEL))
> + return -ENOMEM;
> + if (!zalloc_cpumask_var(&delmask, GFP_KERNEL)) {
> + free_cpumask_var(addmask);
> + return -ENOMEM;
> + }
> +
> + if (!old_count) {
> + if (!zalloc_cpumask_var(&parent->isolated_cpus, GFP_KERNEL)) {
> + retval = -ENOMEM;
> + goto out;
> + }
> + old_count = 1;
> + }
> +
> + retval = -EBUSY;
> + adding = deleting = false;
> + if (newmask)
> + cpumask_copy(addmask, newmask);
> + if (oldmask)
> + deleting = cpumask_andnot(delmask, oldmask, addmask);
> + if (newmask)
> + adding = cpumask_andnot(addmask, newmask, delmask);
> +
> + if (!adding && !deleting)
> + goto out_ok;
> +
> + /*
> + * The cpus to be added must be in the parent's effective_cpus mask
> + * but not in the isolated_cpus mask.
> + */
> + if (!cpumask_subset(addmask, parent->effective_cpus))
> + goto out;
> + if (parent->isolation_count &&
> + cpumask_intersects(parent->isolated_cpus, addmask))
> + goto out;
> +
> + /*
> + * Check if any CPUs in addmask or delmask are in a sibling cpuset.
> + * An empty sibling cpus_allowed means it is the same as parent's
> + * effective_cpus. This checking is skipped if the cpuset is dying.
> + */
> + if (dying)
> + goto updated_isolated_cpus;
> +
> + cpuset_for_each_child(sibling, pos_css, parent) {
> + if ((sibling == cpuset) || !(sibling->css.flags & CSS_ONLINE))
> + continue;
> + if (cpumask_empty(sibling->cpus_allowed))
> + goto out;
> + if (adding &&
> + cpumask_intersects(sibling->cpus_allowed, addmask))
> + goto out;
> + if (deleting &&
> + cpumask_intersects(sibling->cpus_allowed, delmask))
> + goto out;
> + }

Just got the below by echoing 1 into cpuset.sched.domain of a sibling with
"isolated" cpuset.cpus. Guess you are missing proper locking about here
above.

--->8---
[ 7509.905005] =============================
[ 7509.905009] WARNING: suspicious RCU usage
[ 7509.905014] 4.17.0-rc5+ #11 Not tainted
[ 7509.905017] -----------------------------
[ 7509.905023] /home/juri/work/kernel/linux/kernel/cgroup/cgroup.c:3826 cgroup_mutex or RCU read lock required!
[ 7509.905026]
other info that might help us debug this:

[ 7509.905031]
rcu_scheduler_active = 2, debug_locks = 1
[ 7509.905036] 4 locks held by bash/1480:
[ 7509.905039] #0: 00000000bf288709 (sb_writers#6){.+.+}, at: vfs_write+0x18a/0x1b0
[ 7509.905072] #1: 00000000ebf23fc9 (&of->mutex){+.+.}, at: kernfs_fop_write+0xe2/0x1a0
[ 7509.905098] #2: 00000000de7c626e (kn->count#302){.+.+}, at: kernfs_fop_write+0xeb/0x1a0
[ 7509.905124] #3: 00000000a6a2bd9f (cpuset_mutex){+.+.}, at: cpuset_write_u64+0x23/0x140
[ 7509.905149]
stack backtrace:
[ 7509.905156] CPU: 6 PID: 1480 Comm: bash Not tainted 4.17.0-rc5+ #11
[ 7509.905160] Hardware name: LENOVO 30B6S2F900/1030, BIOS S01KT56A 01/15/2018
[ 7509.905164] Call Trace:
[ 7509.905176] dump_stack+0x85/0xcb
[ 7509.905187] css_next_child+0x90/0xd0
[ 7509.905195] update_isolated_cpumask+0x18f/0x2e0
[ 7509.905208] update_flag+0x1f3/0x210
[ 7509.905220] cpuset_write_u64+0xff/0x140
[ 7509.905230] cgroup_file_write+0x178/0x230
[ 7509.905244] kernfs_fop_write+0x113/0x1a0
[ 7509.905254] __vfs_write+0x36/0x180
[ 7509.905264] ? rcu_read_lock_sched_held+0x6b/0x80
[ 7509.905270] ? rcu_sync_lockdep_assert+0x2e/0x60
[ 7509.905278] ? __sb_start_write+0x13e/0x1a0
[ 7509.905283] ? vfs_write+0x18a/0x1b0
[ 7509.905293] vfs_write+0xc1/0x1b0
[ 7509.905302] ksys_write+0x55/0xc0
[ 7509.905317] do_syscall_64+0x60/0x200
[ 7509.905327] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 7509.905333] RIP: 0033:0x7fee4fdfe414
[ 7509.905338] RSP: 002b:00007fff364a80a8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[ 7509.905346] RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00007fee4fdfe414
[ 7509.905350] RDX: 0000000000000002 RSI: 000055eb12f93740 RDI: 0000000000000001
[ 7509.905354] RBP: 000055eb12f93740 R08: 000000000000000a R09: 00007fff364a7c30
[ 7509.905358] R10: 000000000000000a R11: 0000000000000246 R12: 00007fee500cd760
[ 7509.905361] R13: 0000000000000002 R14: 00007fee500c8760 R15: 0000000000000002
--->8---

Best,

- Juri

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