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Revert "sched/core: Prevent race condition between cpuset and __sched_setscheduler()"

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This reverts commit 710da3c8ea.

When changing a thread's scheduling priority, binder calls
sched_setscheduler_nocheck() while holding the node lock and
proc inner lock. This was safe until v5.3 when this change was
introduced where cpuset_read_lock() is called in this path
which can sleep.

This patch was introduced to fix a possible accounting error
in sched deadline (potential oversell of CPU bandwidth) due
to a race condition between cpusets and __sched_setscheduler().
This is not an issue for Android.

This should be fixed in the binder driver, but that may take
some time.

Bug: 151861772
Change-Id: Ica1ef71b3cdcdc509b341ea1b57c41f8ee73794a
Signed-off-by: Todd Kjos <tkjos@google.com>
This commit is contained in:
Todd Kjos 2020-03-27 10:04:16 -07:00 committed by Alistair Delva
parent 553f33f495
commit 669d93f855
3 changed files with 3 additions and 33 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
include/linux/cpuset.h
View File

@ -55,8 +55,6 @@ extern void cpuset_init_smp(void);
extern void cpuset_force_rebuild(void);
extern void cpuset_update_active_cpus(void);
extern void cpuset_wait_for_hotplug(void);
extern void cpuset_read_lock(void);
extern void cpuset_read_unlock(void);
extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
extern void cpuset_cpus_allowed_fallback(struct task_struct *p);
extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
@ -178,9 +176,6 @@ static inline void cpuset_update_active_cpus(void)
static inline void cpuset_wait_for_hotplug(void) { }
static inline void cpuset_read_lock(void) { }
static inline void cpuset_read_unlock(void) { }
static inline void cpuset_cpus_allowed(struct task_struct *p,
struct cpumask *mask)
{

11
kernel/cgroup/cpuset.c
View File

@ -334,17 +334,6 @@ static struct cpuset top_cpuset = {
*/
DEFINE_STATIC_PERCPU_RWSEM(cpuset_rwsem);
void cpuset_read_lock(void)
{
percpu_down_read(&cpuset_rwsem);
}
void cpuset_read_unlock(void)
{
percpu_up_read(&cpuset_rwsem);
}
static DEFINE_SPINLOCK(callback_lock);
static struct workqueue_struct *cpuset_migrate_mm_wq;

20
kernel/sched/core.c
View File

@ -4863,9 +4863,6 @@ recheck:
return retval;
}
if (pi)
cpuset_read_lock();
/*
* Make sure no PI-waiters arrive (or leave) while we are
* changing the priority of the task:
@ -4940,8 +4937,6 @@ change:
if (unlikely(oldpolicy != -1 && oldpolicy != p->policy)) {
policy = oldpolicy = -1;
task_rq_unlock(rq, p, &rf);
if (pi)
cpuset_read_unlock();
goto recheck;
}
@ -5002,10 +4997,8 @@ change:
preempt_disable();
task_rq_unlock(rq, p, &rf);
if (pi) {
cpuset_read_unlock();
if (pi)
rt_mutex_adjust_pi(p);
}
/* Run balance callbacks after we've adjusted the PI chain: */
balance_callback(rq);
@ -5015,8 +5008,6 @@ change:
unlock:
task_rq_unlock(rq, p, &rf);
if (pi)
cpuset_read_unlock();
return retval;
}
@ -5101,14 +5092,9 @@ do_sched_setscheduler(pid_t pid, int policy, struct sched_param __user *param)
rcu_read_lock();
retval = -ESRCH;
p = find_process_by_pid(pid);
if (likely(p))
get_task_struct(p);
rcu_read_unlock();
if (likely(p)) {
if (p != NULL)
retval = sched_setscheduler(p, policy, &lparam);
put_task_struct(p);
}
rcu_read_unlock();
return retval;
}