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- Fix scheduler frequency invariance bug related to overly long tickless periods

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triggering an integer overflow and disabling the feature.
 
 - Fix use-after-free bug in dup_user_cpus_ptr().
 
 - Fix do_set_cpus_allowed() deadlock scenarios related to calling kfree() with
   the pi_lock held. NOTE: the rcu_free() is the 'lazy' solution here - we looked
   at patches to free the structure after the pi_lock got dropped, but that looked
   quite a bit messier - and none of this is truly performance critical. We can
   revisit this if it's too lazy of a solution ...
 
 Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'sched-urgent-2023-01-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler fixes from Ingo Molnar:

 - Fix scheduler frequency invariance bug related to overly long
   tickless periods triggering an integer overflow and disabling the
   feature.

 - Fix use-after-free bug in dup_user_cpus_ptr().

 - Fix do_set_cpus_allowed() deadlock scenarios related to calling
   kfree() with the pi_lock held. NOTE: the rcu_free() is the 'lazy'
   solution here - we looked at patches to free the structure after the
   pi_lock got dropped, but that looked quite a bit messier - and none
   of this is truly performance critical. We can revisit this if it's
   too lazy of a solution ...

* tag 'sched-urgent-2023-01-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/core: Use kfree_rcu() in do_set_cpus_allowed()
  sched/core: Fix use-after-free bug in dup_user_cpus_ptr()
  sched/core: Fix arch_scale_freq_tick() on tickless systems
This commit is contained in:
Linus Torvalds 2023-01-12 16:39:43 -06:00
commit ea66bf8653
1 changed files with 60 additions and 9 deletions
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69
kernel/sched/core.c
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@ -2604,27 +2604,71 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
.user_mask = NULL,
.flags = SCA_USER, /* clear the user requested mask */
};
union cpumask_rcuhead {
cpumask_t cpumask;
struct rcu_head rcu;
};
__do_set_cpus_allowed(p, &ac);
kfree(ac.user_mask);
/*
* Because this is called with p->pi_lock held, it is not possible
* to use kfree() here (when PREEMPT_RT=y), therefore punt to using
* kfree_rcu().
*/
kfree_rcu((union cpumask_rcuhead *)ac.user_mask, rcu);
}
static cpumask_t *alloc_user_cpus_ptr(int node)
{
/*
* See do_set_cpus_allowed() above for the rcu_head usage.
*/
int size = max_t(int, cpumask_size(), sizeof(struct rcu_head));
return kmalloc_node(size, GFP_KERNEL, node);
}
int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
int node)
{
cpumask_t *user_mask;
unsigned long flags;
if (!src->user_cpus_ptr)
/*
* Always clear dst->user_cpus_ptr first as their user_cpus_ptr's
* may differ by now due to racing.
*/
dst->user_cpus_ptr = NULL;
/*
* This check is racy and losing the race is a valid situation.
* It is not worth the extra overhead of taking the pi_lock on
* every fork/clone.
*/
if (data_race(!src->user_cpus_ptr))
return 0;
dst->user_cpus_ptr = kmalloc_node(cpumask_size(), GFP_KERNEL, node);
if (!dst->user_cpus_ptr)
user_mask = alloc_user_cpus_ptr(node);
if (!user_mask)
return -ENOMEM;
/* Use pi_lock to protect content of user_cpus_ptr */
/*
* Use pi_lock to protect content of user_cpus_ptr
*
* Though unlikely, user_cpus_ptr can be reset to NULL by a concurrent
* do_set_cpus_allowed().
*/
raw_spin_lock_irqsave(&src->pi_lock, flags);
cpumask_copy(dst->user_cpus_ptr, src->user_cpus_ptr);
if (src->user_cpus_ptr) {
swap(dst->user_cpus_ptr, user_mask);
cpumask_copy(dst->user_cpus_ptr, src->user_cpus_ptr);
}
raw_spin_unlock_irqrestore(&src->pi_lock, flags);
if (unlikely(user_mask))
kfree(user_mask);
return 0;
}
@ -3581,6 +3625,11 @@ static inline bool rq_has_pinned_tasks(struct rq *rq)
return false;
}
static inline cpumask_t *alloc_user_cpus_ptr(int node)
{
return NULL;
}
#endif /* !CONFIG_SMP */
static void
@ -5504,7 +5553,9 @@ void scheduler_tick(void)
unsigned long thermal_pressure;
u64 resched_latency;
arch_scale_freq_tick();
if (housekeeping_cpu(cpu, HK_TYPE_TICK))
arch_scale_freq_tick();
sched_clock_tick();
rq_lock(rq, &rf);
@ -8239,8 +8290,8 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
if (retval)
goto out_put_task;
user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
if (!user_mask) {
user_mask = alloc_user_cpus_ptr(NUMA_NO_NODE);
if (IS_ENABLED(CONFIG_SMP) && !user_mask) {
retval = -ENOMEM;
goto out_put_task;
}