Messages in this thread | | | Date | Wed, 21 Dec 2022 14:22:56 -0500 | Subject | Re: [PATCH-tip v3] sched: Use kfree_rcu() in do_set_cpus_allowed() | From | Waiman Long <> |
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On 12/5/22 11:39, 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() > may have pi_lock held when calling it. So the following splats may be > printed especially when running with a PREEMPT_RT kernel: > > WARNING: possible circular locking dependency detected > BUG: sleeping function called from invalid context > > To avoid these problems, kfree_rcu() is used instead. An internal > cpumask_rcuhead union is created for the sole purpose of facilitating > the use of kfree_rcu() to free the cpumask. > > Fixes: 851a723e45d1 ("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()") > Suggested-by: Peter Zijlstra <peterz@infradead.org> > Signed-off-by: Waiman Long <longman@redhat.com> > --- > kernel/sched/core.c | 20 +++++++++++++++++--- > 1 file changed, 17 insertions(+), 3 deletions(-) > > [v3: Fix build problem reported by kernel test robot] > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 57e5932f81a9..155b6cfe119a 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2604,9 +2604,19 @@ 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); > } > > int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src, > @@ -8220,7 +8230,7 @@ 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(); > > @@ -8253,7 +8263,11 @@ 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;
Hi Peter,
Is this patch good enough to be merged as commit 851a723e45d1 ("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()") is now in the Linus' tree?
Thanks, Longman
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