Messages in this thread | | | Date | Thu, 22 Dec 2022 15:18:29 -0500 | Subject | Re: [PATCH-tip v3] sched: Use kfree_rcu() in do_set_cpus_allowed() | From | Waiman Long <> |
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On 12/22/22 14:32, Peter Zijlstra wrote: > On Mon, Dec 05, 2022 at 11:39:36AM -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() >> 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; > AFAICT you forgot dup_user_cpus_ptr().
I haven't received any response from you for a while. So it is just a ping. Of course, I am aware that there is another dup_user_cpus_ptr() patch ouststanding. I will of course talk about that when you respond. I also have a pending rwsem patch series waiting for your review:-)
Cheers, Longman
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