* [PATCH-tip] sched: Don't call kfree() in do_set_cpus_allowed()
@ 2022-11-18 19:33 Waiman Long
2022-11-21 10:38 ` Peter Zijlstra
0 siblings, 1 reply; 9+ messages in thread
From: Waiman Long @ 2022-11-18 19:33 UTC (permalink / raw)
To: Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot,
Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira
Cc: Phil Auld, linux-kernel, Waiman Long
Commit 851a723e45d1 ("sched: Always clear user_cpus_ptr in
do_set_cpus_allowed()") may call kfree() if user_cpus_ptr was previously
set. Unfortunately, some of the callers of do_set_cpus_allowed()
may not be in a context where kfree() can be safely called. So the
following splats may be printed:
WARNING: possible circular locking dependency detected
BUG: sleeping function called from invalid context
To avoid these problems without leaking memory, the free cpumask is now
put into a lockless list to be reused in a later sched_setaffinity()
call instead.
Fixes: 851a723e45d1 ("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()")
Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/sched/core.c | 26 +++++++++++++++++++++++---
1 file changed, 23 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 78b2d5cabcc5..8df51b08bb38 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2527,6 +2527,11 @@ int push_cpu_stop(void *arg)
return 0;
}
+/*
+ * A lockless list of user cpumask available to be reused.
+ */
+static LLIST_HEAD(free_cpumasks);
+
/*
* sched_class::set_cpus_allowed must do the below, but is not required to
* actually call this function.
@@ -2606,7 +2611,14 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
};
__do_set_cpus_allowed(p, &ac);
- kfree(ac.user_mask);
+ if (ac.user_mask) {
+ /*
+ * We may not be in a context where kfree() can be called.
+ * Put the free user_mask in free_cpumasks to be freed or
+ * used later.
+ */
+ llist_add((struct llist_node *)ac.user_mask, &free_cpumasks);
+ }
}
int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
@@ -8194,7 +8206,7 @@ __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;
- struct cpumask *user_mask;
+ struct cpumask *user_mask = NULL;
struct task_struct *p;
int retval;
@@ -8229,7 +8241,15 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
if (retval)
goto out_put_task;
- user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
+ /*
+ * Use the element in the free_cpumasks, if available.
+ */
+ if (!llist_empty(&free_cpumasks))
+ user_mask = (struct cpumask *)llist_del_first(&free_cpumasks);
+
+ if (!user_mask)
+ user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
+
if (!user_mask) {
retval = -ENOMEM;
goto out_put_task;
--
2.31.1
^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [PATCH-tip] sched: Don't call kfree() in do_set_cpus_allowed()
2022-11-18 19:33 [PATCH-tip] sched: Don't call kfree() in do_set_cpus_allowed() Waiman Long
@ 2022-11-21 10:38 ` Peter Zijlstra
2022-11-21 15:04 ` Waiman Long
0 siblings, 1 reply; 9+ messages in thread
From: Peter Zijlstra @ 2022-11-21 10:38 UTC (permalink / raw)
To: Waiman Long
Cc: Ingo Molnar, Juri Lelli, Vincent Guittot, Dietmar Eggemann,
Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Phil Auld, linux-kernel
On Fri, Nov 18, 2022 at 02:33:02PM -0500, Waiman Long wrote:
> Commit 851a723e45d1 ("sched: Always clear user_cpus_ptr in
> do_set_cpus_allowed()") may call kfree() if user_cpus_ptr was previously
> set. Unfortunately, some of the callers of do_set_cpus_allowed()
'some' ? There's only 3 or so, which one triggers this?
> may not be in a context where kfree() can be safely called. So the
> following splats may be printed:
>
> WARNING: possible circular locking dependency detected
> BUG: sleeping function called from invalid context
>
> To avoid these problems without leaking memory, the free cpumask is now
> put into a lockless list to be reused in a later sched_setaffinity()
> call instead.
Urgh.. depending on which of the callsites it is, it's probably simpler
to just rework the caller to not use do_set_cpus_allowed(), no?
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH-tip] sched: Don't call kfree() in do_set_cpus_allowed()
2022-11-21 10:38 ` Peter Zijlstra
@ 2022-11-21 15:04 ` Waiman Long
2022-11-22 12:37 ` Peter Zijlstra
0 siblings, 1 reply; 9+ messages in thread
From: Waiman Long @ 2022-11-21 15:04 UTC (permalink / raw)
To: Peter Zijlstra
Cc: Ingo Molnar, Juri Lelli, Vincent Guittot, Dietmar Eggemann,
Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Phil Auld, linux-kernel
On 11/21/22 05:38, Peter Zijlstra wrote:
> On Fri, Nov 18, 2022 at 02:33:02PM -0500, Waiman Long wrote:
>> Commit 851a723e45d1 ("sched: Always clear user_cpus_ptr in
>> do_set_cpus_allowed()") may call kfree() if user_cpus_ptr was previously
>> set. Unfortunately, some of the callers of do_set_cpus_allowed()
> 'some' ? There's only 3 or so, which one triggers this?
It happenned at __kthread_bind_mask() where do_set_cpus_allowed() is
called with pi_lock held.
[ 1084.820105] <TASK>
[ 1084.820110] dump_stack_lvl+0x57/0x81
[ 1084.820117] check_noncircular+0x103/0x120
[ 10[ 1084.820160] lock_acquire+0xba/0x230
[ 1084.820164] ? kfree+0x10f/0x380
[ 1084.820172] ? do_set_cpus_allowed+0x40/0x60
[ 1084.820181] rt_spin_lock+0x27/0xe0
[ 1084.820184] ? kfree+0x10f/0x380
[ 1084.820188] kfree+0x10f/0x380
[ 1084.820195] do_set_cpus_allowed+0x40/0x60
[ 1084.820203] kthread_bind_mask+0x4a/0x70
[ 1084.820211] create_worker+0xfb/0x1a0
[ 1084.820220] worker_thread+0x2e3/0x3c0
[ 1084.820226] ? process_one_work+0x450/0x450
[ 1084.820230] kthread+0x111/0x130
[ 1084.820236] ? kthread_complete_and_exit+0x20/0x20
[ 1084.820244] ret_from_fork+0x22/0x30
[ 1084.820258] </TASK>
[ 1084.820260] BUG: sleeping function called from invalid context at
kernel/locking/spinlock_rt.c:46
It shows up with PREEMPT_RT kernel.
>
>> may not be in a context where kfree() can be safely called. So the
>> following splats may be printed:
>>
>> WARNING: possible circular locking dependency detected
>> BUG: sleeping function called from invalid context
>>
>> To avoid these problems without leaking memory, the free cpumask is now
>> put into a lockless list to be reused in a later sched_setaffinity()
>> call instead.
> Urgh.. depending on which of the callsites it is, it's probably simpler
> to just rework the caller to not use do_set_cpus_allowed(), no?
Maybe. One thing that I am not clear about is why user_cpus_ptr is set
in the first place.
Cheers,
Longman
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH-tip] sched: Don't call kfree() in do_set_cpus_allowed()
2022-11-21 15:04 ` Waiman Long
@ 2022-11-22 12:37 ` Peter Zijlstra
2022-11-22 15:23 ` Waiman Long
0 siblings, 1 reply; 9+ messages in thread
From: Peter Zijlstra @ 2022-11-22 12:37 UTC (permalink / raw)
To: Waiman Long
Cc: Ingo Molnar, Juri Lelli, Vincent Guittot, Dietmar Eggemann,
Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Phil Auld, linux-kernel,
Paul McKenney
On Mon, Nov 21, 2022 at 10:04:33AM -0500, Waiman Long wrote:
>
> On 11/21/22 05:38, Peter Zijlstra wrote:
> > On Fri, Nov 18, 2022 at 02:33:02PM -0500, Waiman Long wrote:
> > > Commit 851a723e45d1 ("sched: Always clear user_cpus_ptr in
> > > do_set_cpus_allowed()") may call kfree() if user_cpus_ptr was previously
> > > set. Unfortunately, some of the callers of do_set_cpus_allowed()
> > 'some' ? There's only 3 or so, which one triggers this?
>
> It happenned at __kthread_bind_mask() where do_set_cpus_allowed() is called
> with pi_lock held.
>
> [ 1084.820105] <TASK>
> [ 1084.820110] dump_stack_lvl+0x57/0x81
> [ 1084.820117] check_noncircular+0x103/0x120
> [ 10[ 1084.820160] lock_acquire+0xba/0x230
> [ 1084.820164] ? kfree+0x10f/0x380
> [ 1084.820172] ? do_set_cpus_allowed+0x40/0x60
> [ 1084.820181] rt_spin_lock+0x27/0xe0
> [ 1084.820184] ? kfree+0x10f/0x380
> [ 1084.820188] kfree+0x10f/0x380
> [ 1084.820195] do_set_cpus_allowed+0x40/0x60
> [ 1084.820203] kthread_bind_mask+0x4a/0x70
> [ 1084.820211] create_worker+0xfb/0x1a0
> [ 1084.820220] worker_thread+0x2e3/0x3c0
> [ 1084.820226] ? process_one_work+0x450/0x450
> [ 1084.820230] kthread+0x111/0x130
> [ 1084.820236] ? kthread_complete_and_exit+0x20/0x20
> [ 1084.820244] ret_from_fork+0x22/0x30
> [ 1084.820258] </TASK>
> [ 1084.820260] BUG: sleeping function called from invalid context at
> kernel/locking/spinlock_rt.c:46
>
> It shows up with PREEMPT_RT kernel.
Oh, I see ..
> Maybe. One thing that I am not clear about is why user_cpus_ptr is set in
> the first place.
Perhaps someone set an affinity on kthreadd ?
But I'm thinking this exact problem is also possible (rather more likely
even) with select_fallback_rq() that too holds pi_lock (which account
for both other users of this function).
Bah.
And the allocation is just the one long in size (for small configs)
which is just enough space for a single linked list like you had.
Urgh.
The below is yuck too, and I'm not sure Paul wants us to use
kvfree_call_rcu() without its wrapper.
---
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 78b2d5cabcc5..0d0af0fc7fcf 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2606,7 +2606,12 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
};
__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().
+ */
+ kvfree_call_rcu((struct rcu_head *)ac.user_mask, (rcu_callback_t)0);
}
int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
@@ -8196,7 +8201,7 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
struct affinity_context ac;
struct cpumask *user_mask;
struct task_struct *p;
- int retval;
+ int retval, size;
rcu_read_lock();
@@ -8229,7 +8234,11 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
if (retval)
goto out_put_task;
- user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
+ /*
+ * See do_set_cpus_allowed() for the rcu_head usage.
+ */
+ size = max_t(int, cpumask_size(), sizeof(struct rcu_head));
+ user_mask = kmalloc(size, GFP_KERNEL);
if (!user_mask) {
retval = -ENOMEM;
goto out_put_task;
^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [PATCH-tip] sched: Don't call kfree() in do_set_cpus_allowed()
2022-11-22 12:37 ` Peter Zijlstra
@ 2022-11-22 15:23 ` Waiman Long
2022-11-22 16:33 ` Paul E. McKenney
2022-11-22 19:24 ` Peter Zijlstra
0 siblings, 2 replies; 9+ messages in thread
From: Waiman Long @ 2022-11-22 15:23 UTC (permalink / raw)
To: Peter Zijlstra
Cc: Ingo Molnar, Juri Lelli, Vincent Guittot, Dietmar Eggemann,
Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Phil Auld, linux-kernel,
Paul McKenney
On 11/22/22 07:37, Peter Zijlstra wrote:
> On Mon, Nov 21, 2022 at 10:04:33AM -0500, Waiman Long wrote:
>> On 11/21/22 05:38, Peter Zijlstra wrote:
>>> On Fri, Nov 18, 2022 at 02:33:02PM -0500, Waiman Long wrote:
>>>> Commit 851a723e45d1 ("sched: Always clear user_cpus_ptr in
>>>> do_set_cpus_allowed()") may call kfree() if user_cpus_ptr was previously
>>>> set. Unfortunately, some of the callers of do_set_cpus_allowed()
>>> 'some' ? There's only 3 or so, which one triggers this?
>> It happenned at __kthread_bind_mask() where do_set_cpus_allowed() is called
>> with pi_lock held.
>>
>> [ 1084.820105] <TASK>
>> [ 1084.820110] dump_stack_lvl+0x57/0x81
>> [ 1084.820117] check_noncircular+0x103/0x120
>> [ 10[ 1084.820160] lock_acquire+0xba/0x230
>> [ 1084.820164] ? kfree+0x10f/0x380
>> [ 1084.820172] ? do_set_cpus_allowed+0x40/0x60
>> [ 1084.820181] rt_spin_lock+0x27/0xe0
>> [ 1084.820184] ? kfree+0x10f/0x380
>> [ 1084.820188] kfree+0x10f/0x380
>> [ 1084.820195] do_set_cpus_allowed+0x40/0x60
>> [ 1084.820203] kthread_bind_mask+0x4a/0x70
>> [ 1084.820211] create_worker+0xfb/0x1a0
>> [ 1084.820220] worker_thread+0x2e3/0x3c0
>> [ 1084.820226] ? process_one_work+0x450/0x450
>> [ 1084.820230] kthread+0x111/0x130
>> [ 1084.820236] ? kthread_complete_and_exit+0x20/0x20
>> [ 1084.820244] ret_from_fork+0x22/0x30
>> [ 1084.820258] </TASK>
>> [ 1084.820260] BUG: sleeping function called from invalid context at
>> kernel/locking/spinlock_rt.c:46
>>
>> It shows up with PREEMPT_RT kernel.
> Oh, I see ..
>
>> Maybe. One thing that I am not clear about is why user_cpus_ptr is set in
>> the first place.
> Perhaps someone set an affinity on kthreadd ?
>
> But I'm thinking this exact problem is also possible (rather more likely
> even) with select_fallback_rq() that too holds pi_lock (which account
> for both other users of this function).
>
> Bah.
>
> And the allocation is just the one long in size (for small configs)
> which is just enough space for a single linked list like you had.
That is exactly the reason why I use lockless list.
>
> Urgh.
>
> The below is yuck too, and I'm not sure Paul wants us to use
> kvfree_call_rcu() without its wrapper.
>
> ---
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 78b2d5cabcc5..0d0af0fc7fcf 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2606,7 +2606,12 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
> };
>
> __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().
> + */
> + kvfree_call_rcu((struct rcu_head *)ac.user_mask, (rcu_callback_t)0);
> }
I guess you need to do a NULL check before calling kvfree_call_rcu() as
I don't think kvfree_call_rcu() does that. Also it is unlikely that we
need to call it.
>
> int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
> @@ -8196,7 +8201,7 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
> struct affinity_context ac;
> struct cpumask *user_mask;
> struct task_struct *p;
> - int retval;
> + int retval, size;
>
> rcu_read_lock();
>
> @@ -8229,7 +8234,11 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
> if (retval)
> goto out_put_task;
>
> - user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
> + /*
> + * See do_set_cpus_allowed() for the rcu_head usage.
> + */
> + size = max_t(int, cpumask_size(), sizeof(struct rcu_head));
> + user_mask = kmalloc(size, GFP_KERNEL);
> if (!user_mask) {
> retval = -ENOMEM;
> goto out_put_task;
I guess that will work too. Just like you, I am a bit uneasy to call
into kvfree_call_rcu() directly as it may change in the future. How about
iff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 78b2d5cabcc5..5fac4aa6ac7f 100644
--- a/kernel/sched/core.c
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 78b2d5cabcc5..5fac4aa6ac7f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2593,6 +2593,11 @@ __do_set_cpus_allowed(struct task_struct *p,
struct affinity_context *ctx)
set_next_task(rq, p);
}
+union cpumask_rcuhead {
+ void *cpumask;
+ struct rcu_head rcu;
+};
+
/*
* Used for kthread_bind() and select_fallback_rq(), in both cases the
user
* affinity (if any) should be destroyed too.
@@ -2606,7 +2611,12 @@ void do_set_cpus_allowed(struct task_struct *p,
const struct cpumask *new_mask)
};
__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);
}
int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
@@ -8196,7 +8206,7 @@ long sched_setaffinity(pid_t pid, const struct
cpumask *in_mask)
struct affinity_context ac;
struct cpumask *user_mask;
struct task_struct *p;
- int retval;
+ int retval, size;
rcu_read_lock();
@@ -8229,7 +8239,11 @@ long sched_setaffinity(pid_t pid, const struct
cpumask *in_mask)
if (retval)
goto out_put_task;
- user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
+ /*
+ * See do_set_cpus_allowed() for the rcu_head usage.
+ */
+ size = max_t(int, cpumask_size(), sizeof(union cpumask_rcuhead));
+ user_mask = kmalloc(size, GFP_KERNEL);
if (!user_mask) {
retval = -ENOMEM;
goto out_put_task;
Cheers,
Longman
^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [PATCH-tip] sched: Don't call kfree() in do_set_cpus_allowed()
2022-11-22 15:23 ` Waiman Long
@ 2022-11-22 16:33 ` Paul E. McKenney
2022-11-22 19:24 ` Peter Zijlstra
1 sibling, 0 replies; 9+ messages in thread
From: Paul E. McKenney @ 2022-11-22 16:33 UTC (permalink / raw)
To: Waiman Long
Cc: Peter Zijlstra, Ingo Molnar, Juri Lelli, Vincent Guittot,
Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Phil Auld, linux-kernel
On Tue, Nov 22, 2022 at 10:23:43AM -0500, Waiman Long wrote:
> On 11/22/22 07:37, Peter Zijlstra wrote:
> > On Mon, Nov 21, 2022 at 10:04:33AM -0500, Waiman Long wrote:
> > > On 11/21/22 05:38, Peter Zijlstra wrote:
> > > > On Fri, Nov 18, 2022 at 02:33:02PM -0500, Waiman Long wrote:
> > > > > Commit 851a723e45d1 ("sched: Always clear user_cpus_ptr in
> > > > > do_set_cpus_allowed()") may call kfree() if user_cpus_ptr was previously
> > > > > set. Unfortunately, some of the callers of do_set_cpus_allowed()
> > > > 'some' ? There's only 3 or so, which one triggers this?
> > > It happenned at __kthread_bind_mask() where do_set_cpus_allowed() is called
> > > with pi_lock held.
> > >
> > > [ 1084.820105] <TASK>
> > > [ 1084.820110] dump_stack_lvl+0x57/0x81
> > > [ 1084.820117] check_noncircular+0x103/0x120
> > > [ 10[ 1084.820160] lock_acquire+0xba/0x230
> > > [ 1084.820164] ? kfree+0x10f/0x380
> > > [ 1084.820172] ? do_set_cpus_allowed+0x40/0x60
> > > [ 1084.820181] rt_spin_lock+0x27/0xe0
> > > [ 1084.820184] ? kfree+0x10f/0x380
> > > [ 1084.820188] kfree+0x10f/0x380
> > > [ 1084.820195] do_set_cpus_allowed+0x40/0x60
> > > [ 1084.820203] kthread_bind_mask+0x4a/0x70
> > > [ 1084.820211] create_worker+0xfb/0x1a0
> > > [ 1084.820220] worker_thread+0x2e3/0x3c0
> > > [ 1084.820226] ? process_one_work+0x450/0x450
> > > [ 1084.820230] kthread+0x111/0x130
> > > [ 1084.820236] ? kthread_complete_and_exit+0x20/0x20
> > > [ 1084.820244] ret_from_fork+0x22/0x30
> > > [ 1084.820258] </TASK>
> > > [ 1084.820260] BUG: sleeping function called from invalid context at
> > > kernel/locking/spinlock_rt.c:46
> > >
> > > It shows up with PREEMPT_RT kernel.
> > Oh, I see ..
> >
> > > Maybe. One thing that I am not clear about is why user_cpus_ptr is set in
> > > the first place.
> > Perhaps someone set an affinity on kthreadd ?
> >
> > But I'm thinking this exact problem is also possible (rather more likely
> > even) with select_fallback_rq() that too holds pi_lock (which account
> > for both other users of this function).
> >
> > Bah.
> >
> > And the allocation is just the one long in size (for small configs)
> > which is just enough space for a single linked list like you had.
> That is exactly the reason why I use lockless list.
> >
> > Urgh.
> >
> > The below is yuck too, and I'm not sure Paul wants us to use
> > kvfree_call_rcu() without its wrapper.
> >
> > ---
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 78b2d5cabcc5..0d0af0fc7fcf 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -2606,7 +2606,12 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
> > };
> > __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().
> > + */
> > + kvfree_call_rcu((struct rcu_head *)ac.user_mask, (rcu_callback_t)0);
> > }
>
> I guess you need to do a NULL check before calling kvfree_call_rcu() as I
> don't think kvfree_call_rcu() does that. Also it is unlikely that we need to
> call it.
Indeed, the NULL check is in kvfree_rcu_arg_2(). By the time you get
to kvfree_call_rcu, the pointer is assumed to be non-NULL.
> > int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
> > @@ -8196,7 +8201,7 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
> > struct affinity_context ac;
> > struct cpumask *user_mask;
> > struct task_struct *p;
> > - int retval;
> > + int retval, size;
> > rcu_read_lock();
> > @@ -8229,7 +8234,11 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
> > if (retval)
> > goto out_put_task;
> > - user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
> > + /*
> > + * See do_set_cpus_allowed() for the rcu_head usage.
> > + */
> > + size = max_t(int, cpumask_size(), sizeof(struct rcu_head));
> > + user_mask = kmalloc(size, GFP_KERNEL);
> > if (!user_mask) {
> > retval = -ENOMEM;
> > goto out_put_task;
>
> I guess that will work too. Just like you, I am a bit uneasy to call into
> kvfree_call_rcu() directly as it may change in the future. How about
>
> iff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 78b2d5cabcc5..5fac4aa6ac7f 100644
> --- a/kernel/sched/core.c
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 78b2d5cabcc5..5fac4aa6ac7f 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2593,6 +2593,11 @@ __do_set_cpus_allowed(struct task_struct *p, struct
> affinity_context *ctx)
> set_next_task(rq, p);
> }
>
> +union cpumask_rcuhead {
> + void *cpumask;
> + struct rcu_head rcu;
> +};
> +
> /*
> * Used for kthread_bind() and select_fallback_rq(), in both cases the user
> * affinity (if any) should be destroyed too.
> @@ -2606,7 +2611,12 @@ void do_set_cpus_allowed(struct task_struct *p, const
> struct cpumask *new_mask)
> };
>
> __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);
This looks plausible to me.
Thanx, Paul
> }
>
> int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
> @@ -8196,7 +8206,7 @@ long sched_setaffinity(pid_t pid, const struct cpumask
> *in_mask)
> struct affinity_context ac;
> struct cpumask *user_mask;
> struct task_struct *p;
> - int retval;
> + int retval, size;
>
> rcu_read_lock();
>
> @@ -8229,7 +8239,11 @@ long sched_setaffinity(pid_t pid, const struct
> cpumask *in_mask)
> if (retval)
> goto out_put_task;
>
> - user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
> + /*
> + * See do_set_cpus_allowed() for the rcu_head usage.
> + */
> + size = max_t(int, cpumask_size(), sizeof(union cpumask_rcuhead));
> + user_mask = kmalloc(size, GFP_KERNEL);
> if (!user_mask) {
> retval = -ENOMEM;
> goto out_put_task;
>
> Cheers,
> Longman
>
>
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH-tip] sched: Don't call kfree() in do_set_cpus_allowed()
2022-11-22 15:23 ` Waiman Long
2022-11-22 16:33 ` Paul E. McKenney
@ 2022-11-22 19:24 ` Peter Zijlstra
2022-11-22 19:30 ` Waiman Long
1 sibling, 1 reply; 9+ messages in thread
From: Peter Zijlstra @ 2022-11-22 19:24 UTC (permalink / raw)
To: Waiman Long
Cc: Ingo Molnar, Juri Lelli, Vincent Guittot, Dietmar Eggemann,
Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Phil Auld, linux-kernel,
Paul McKenney
On Tue, Nov 22, 2022 at 10:23:43AM -0500, Waiman Long wrote:
> index 78b2d5cabcc5..5fac4aa6ac7f 100644
> --- a/kernel/sched/core.c
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 78b2d5cabcc5..5fac4aa6ac7f 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2593,6 +2593,11 @@ __do_set_cpus_allowed(struct task_struct *p, struct
> affinity_context *ctx)
> set_next_task(rq, p);
> }
>
> +union cpumask_rcuhead {
> + void *cpumask;
> + struct rcu_head rcu;
> +};
> +
Hehe; I had this union too; I just figured it'd be nice to not have to
spend these 4 lines to express this. Esp. since we're casting pointers
*anyway*.
> /*
> * Used for kthread_bind() and select_fallback_rq(), in both cases the user
> * affinity (if any) should be destroyed too.
> @@ -2606,7 +2611,12 @@ void do_set_cpus_allowed(struct task_struct *p, const
> struct cpumask *new_mask)
> };
>
> __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);
> }
>
> int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
> @@ -8196,7 +8206,7 @@ long sched_setaffinity(pid_t pid, const struct cpumask
> *in_mask)
> struct affinity_context ac;
> struct cpumask *user_mask;
> struct task_struct *p;
> - int retval;
> + int retval, size;
>
> rcu_read_lock();
>
> @@ -8229,7 +8239,11 @@ long sched_setaffinity(pid_t pid, const struct
> cpumask *in_mask)
> if (retval)
> goto out_put_task;
>
> - user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
> + /*
> + * See do_set_cpus_allowed() for the rcu_head usage.
> + */
> + size = max_t(int, cpumask_size(), sizeof(union cpumask_rcuhead));
> + user_mask = kmalloc(size, GFP_KERNEL);
> if (!user_mask) {
> retval = -ENOMEM;
> goto out_put_task;
>
We also should fix the allocation in dup_user_cpus_ptr() -- perhaps pull
the thing into a helper.
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH-tip] sched: Don't call kfree() in do_set_cpus_allowed()
2022-11-22 19:24 ` Peter Zijlstra
@ 2022-11-22 19:30 ` Waiman Long
2022-11-22 19:58 ` Peter Zijlstra
0 siblings, 1 reply; 9+ messages in thread
From: Waiman Long @ 2022-11-22 19:30 UTC (permalink / raw)
To: Peter Zijlstra
Cc: Ingo Molnar, Juri Lelli, Vincent Guittot, Dietmar Eggemann,
Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Phil Auld, linux-kernel,
Paul McKenney
On 11/22/22 14:24, Peter Zijlstra wrote:
> On Tue, Nov 22, 2022 at 10:23:43AM -0500, Waiman Long wrote:
>> index 78b2d5cabcc5..5fac4aa6ac7f 100644
>> --- a/kernel/sched/core.c
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 78b2d5cabcc5..5fac4aa6ac7f 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -2593,6 +2593,11 @@ __do_set_cpus_allowed(struct task_struct *p, struct
>> affinity_context *ctx)
>> set_next_task(rq, p);
>> }
>>
>> +union cpumask_rcuhead {
>> + void *cpumask;
>> + struct rcu_head rcu;
>> +};
>> +
> Hehe; I had this union too; I just figured it'd be nice to not have to
> spend these 4 lines to express this. Esp. since we're casting pointers
> *anyway*.
Well, that is true. As long as the NULL check is there, I am OK with
calling kvfree_call_rcu() directly if Paul doesn't object.
>> /*
>> * Used for kthread_bind() and select_fallback_rq(), in both cases the user
>> * affinity (if any) should be destroyed too.
>> @@ -2606,7 +2611,12 @@ void do_set_cpus_allowed(struct task_struct *p, const
>> struct cpumask *new_mask)
>> };
>>
>> __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);
>> }
>>
>> int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
>> @@ -8196,7 +8206,7 @@ long sched_setaffinity(pid_t pid, const struct cpumask
>> *in_mask)
>> struct affinity_context ac;
>> struct cpumask *user_mask;
>> struct task_struct *p;
>> - int retval;
>> + int retval, size;
>>
>> rcu_read_lock();
>>
>> @@ -8229,7 +8239,11 @@ long sched_setaffinity(pid_t pid, const struct
>> cpumask *in_mask)
>> if (retval)
>> goto out_put_task;
>>
>> - user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
>> + /*
>> + * See do_set_cpus_allowed() for the rcu_head usage.
>> + */
>> + size = max_t(int, cpumask_size(), sizeof(union cpumask_rcuhead));
>> + user_mask = kmalloc(size, GFP_KERNEL);
>> if (!user_mask) {
>> retval = -ENOMEM;
>> goto out_put_task;
>>
> We also should fix the allocation in dup_user_cpus_ptr() -- perhaps pull
> the thing into a helper.
>
I have just sent out a new patch to fix that before I saw your email. I
do forgot to put -tip in the subject line.
Cheers,
Longman
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH-tip] sched: Don't call kfree() in do_set_cpus_allowed()
2022-11-22 19:30 ` Waiman Long
@ 2022-11-22 19:58 ` Peter Zijlstra
0 siblings, 0 replies; 9+ messages in thread
From: Peter Zijlstra @ 2022-11-22 19:58 UTC (permalink / raw)
To: Waiman Long
Cc: Ingo Molnar, Juri Lelli, Vincent Guittot, Dietmar Eggemann,
Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Phil Auld, linux-kernel,
Paul McKenney
On Tue, Nov 22, 2022 at 02:30:38PM -0500, Waiman Long wrote:
> I have just sent out a new patch to fix that before I saw your email. I do
> forgot to put -tip in the subject line.
I found it; I'll stare at it in the morning. Things don't seem to want
to make much sense anymore today :-)
^ permalink raw reply [flat|nested] 9+ messages in thread
end of thread, other threads:[~2022-11-22 19:59 UTC | newest]
Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-11-18 19:33 [PATCH-tip] sched: Don't call kfree() in do_set_cpus_allowed() Waiman Long
2022-11-21 10:38 ` Peter Zijlstra
2022-11-21 15:04 ` Waiman Long
2022-11-22 12:37 ` Peter Zijlstra
2022-11-22 15:23 ` Waiman Long
2022-11-22 16:33 ` Paul E. McKenney
2022-11-22 19:24 ` Peter Zijlstra
2022-11-22 19:30 ` Waiman Long
2022-11-22 19:58 ` Peter Zijlstra
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