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sched: Always preserve the user requested cpumask
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Unconditionally preserve the user requested cpumask on
sched_setaffinity() calls. This allows using it outside of the fairly
narrow restrict_cpus_allowed_ptr() use-case and fix some cpuset issues
that currently suffer destruction of cpumasks.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220922180041.1768141-3-longman@redhat.com
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Waiman Long authored and Peter Zijlstra committed Oct 27, 2022
1 parent 713a2e2 commit 8f9ea86
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Showing 2 changed files with 72 additions and 55 deletions.
119 changes: 64 additions & 55 deletions kernel/sched/core.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2540,6 +2540,12 @@ void set_cpus_allowed_common(struct task_struct *p, struct affinity_context *ctx

cpumask_copy(&p->cpus_mask, ctx->new_mask);
p->nr_cpus_allowed = cpumask_weight(ctx->new_mask);

/*
* Swap in a new user_cpus_ptr if SCA_USER flag set
*/
if (ctx->flags & SCA_USER)
swap(p->user_cpus_ptr, ctx->user_mask);
}

static void
Expand Down Expand Up @@ -2600,14 +2606,19 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
int node)
{
unsigned long flags;

if (!src->user_cpus_ptr)
return 0;

dst->user_cpus_ptr = kmalloc_node(cpumask_size(), GFP_KERNEL, node);
if (!dst->user_cpus_ptr)
return -ENOMEM;

/* Use pi_lock to protect content of user_cpus_ptr */
raw_spin_lock_irqsave(&src->pi_lock, flags);
cpumask_copy(dst->user_cpus_ptr, src->user_cpus_ptr);
raw_spin_unlock_irqrestore(&src->pi_lock, flags);
return 0;
}

Expand Down Expand Up @@ -2856,7 +2867,6 @@ static int __set_cpus_allowed_ptr_locked(struct task_struct *p,
const struct cpumask *cpu_allowed_mask = task_cpu_possible_mask(p);
const struct cpumask *cpu_valid_mask = cpu_active_mask;
bool kthread = p->flags & PF_KTHREAD;
struct cpumask *user_mask = NULL;
unsigned int dest_cpu;
int ret = 0;

Expand Down Expand Up @@ -2915,14 +2925,7 @@ static int __set_cpus_allowed_ptr_locked(struct task_struct *p,

__do_set_cpus_allowed(p, ctx);

if (ctx->flags & SCA_USER)
user_mask = clear_user_cpus_ptr(p);

ret = affine_move_task(rq, p, rf, dest_cpu, ctx->flags);

kfree(user_mask);

return ret;
return affine_move_task(rq, p, rf, dest_cpu, ctx->flags);

out:
task_rq_unlock(rq, p, rf);
Expand Down Expand Up @@ -2962,27 +2965,25 @@ EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr);

/*
* Change a given task's CPU affinity to the intersection of its current
* affinity mask and @subset_mask, writing the resulting mask to @new_mask
* and pointing @p->user_cpus_ptr to a copy of the old mask.
* affinity mask and @subset_mask, writing the resulting mask to @new_mask.
* If user_cpus_ptr is defined, use it as the basis for restricting CPU
* affinity or use cpu_online_mask instead.
*
* If the resulting mask is empty, leave the affinity unchanged and return
* -EINVAL.
*/
static int restrict_cpus_allowed_ptr(struct task_struct *p,
struct cpumask *new_mask,
const struct cpumask *subset_mask)
{
struct cpumask *user_mask = NULL;
struct affinity_context ac;
struct affinity_context ac = {
.new_mask = new_mask,
.flags = 0,
};
struct rq_flags rf;
struct rq *rq;
int err;

if (!p->user_cpus_ptr) {
user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
if (!user_mask)
return -ENOMEM;
}

rq = task_rq_lock(p, &rf);

/*
Expand All @@ -2995,29 +2996,15 @@ static int restrict_cpus_allowed_ptr(struct task_struct *p,
goto err_unlock;
}

if (!cpumask_and(new_mask, &p->cpus_mask, subset_mask)) {
if (!cpumask_and(new_mask, task_user_cpus(p), subset_mask)) {
err = -EINVAL;
goto err_unlock;
}

/*
* We're about to butcher the task affinity, so keep track of what
* the user asked for in case we're able to restore it later on.
*/
if (user_mask) {
cpumask_copy(user_mask, p->cpus_ptr);
p->user_cpus_ptr = user_mask;
}

ac = (struct affinity_context){
.new_mask = new_mask,
};

return __set_cpus_allowed_ptr_locked(p, &ac, rq, &rf);

err_unlock:
task_rq_unlock(rq, p, &rf);
kfree(user_mask);
return err;
}

Expand Down Expand Up @@ -3071,33 +3058,25 @@ __sched_setaffinity(struct task_struct *p, struct affinity_context *ctx);

/*
* Restore the affinity of a task @p which was previously restricted by a
* call to force_compatible_cpus_allowed_ptr(). This will clear (and free)
* @p->user_cpus_ptr.
* call to force_compatible_cpus_allowed_ptr().
*
* It is the caller's responsibility to serialise this with any calls to
* force_compatible_cpus_allowed_ptr(@p).
*/
void relax_compatible_cpus_allowed_ptr(struct task_struct *p)
{
struct cpumask *user_mask = p->user_cpus_ptr;
struct affinity_context ac = {
.new_mask = user_mask,
.new_mask = task_user_cpus(p),
.flags = 0,
};
unsigned long flags;
int ret;

/*
* Try to restore the old affinity mask. If this fails, then
* we free the mask explicitly to avoid it being inherited across
* a subsequent fork().
* Try to restore the old affinity mask with __sched_setaffinity().
* Cpuset masking will be done there too.
*/
if (!user_mask || !__sched_setaffinity(p, &ac))
return;

raw_spin_lock_irqsave(&p->pi_lock, flags);
user_mask = clear_user_cpus_ptr(p);
raw_spin_unlock_irqrestore(&p->pi_lock, flags);

kfree(user_mask);
ret = __sched_setaffinity(p, &ac);
WARN_ON_ONCE(ret);
}

void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
Expand Down Expand Up @@ -8136,7 +8115,7 @@ __sched_setaffinity(struct task_struct *p, struct affinity_context *ctx)
retval = dl_task_check_affinity(p, new_mask);
if (retval)
goto out_free_new_mask;
again:

retval = __set_cpus_allowed_ptr(p, ctx);
if (retval)
goto out_free_new_mask;
Expand All @@ -8148,7 +8127,24 @@ __sched_setaffinity(struct task_struct *p, struct affinity_context *ctx)
* Just reset the cpumask to the cpuset's cpus_allowed.
*/
cpumask_copy(new_mask, cpus_allowed);
goto again;

/*
* If SCA_USER is set, a 2nd call to __set_cpus_allowed_ptr()
* will restore the previous user_cpus_ptr value.
*
* In the unlikely event a previous user_cpus_ptr exists,
* we need to further restrict the mask to what is allowed
* by that old user_cpus_ptr.
*/
if (unlikely((ctx->flags & SCA_USER) && ctx->user_mask)) {
bool empty = !cpumask_and(new_mask, new_mask,
ctx->user_mask);

if (WARN_ON_ONCE(empty))
cpumask_copy(new_mask, cpus_allowed);
}
__set_cpus_allowed_ptr(p, ctx);
retval = -EINVAL;
}

out_free_new_mask:
Expand All @@ -8160,9 +8156,8 @@ __sched_setaffinity(struct task_struct *p, struct affinity_context *ctx)

long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
{
struct affinity_context ac = {
.new_mask = in_mask,
};
struct affinity_context ac;
struct cpumask *user_mask;
struct task_struct *p;
int retval;

Expand Down Expand Up @@ -8197,7 +8192,21 @@ 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) {
retval = -ENOMEM;
goto out_put_task;
}
cpumask_copy(user_mask, in_mask);
ac = (struct affinity_context){
.new_mask = in_mask,
.user_mask = user_mask,
.flags = SCA_USER,
};

retval = __sched_setaffinity(p, &ac);
kfree(ac.user_mask);

out_put_task:
put_task_struct(p);
return retval;
Expand Down
8 changes: 8 additions & 0 deletions kernel/sched/sched.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1878,6 +1878,13 @@ static inline void dirty_sched_domain_sysctl(int cpu)
#endif

extern int sched_update_scaling(void);

static inline const struct cpumask *task_user_cpus(struct task_struct *p)
{
if (!p->user_cpus_ptr)
return cpu_possible_mask; /* &init_task.cpus_mask */
return p->user_cpus_ptr;
}
#endif /* CONFIG_SMP */

#include "stats.h"
Expand Down Expand Up @@ -2147,6 +2154,7 @@ extern const u32 sched_prio_to_wmult[40];

struct affinity_context {
const struct cpumask *new_mask;
struct cpumask *user_mask;
unsigned int flags;
};

Expand Down

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