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

[Juri Lelli]

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