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Date: Fri, 21 May 2021 13:17:11 -0700
From: Andrei Vagin <avagin@...il.com>
To: Peter Oskolkov <posk@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
Paul Turner <pjt@...gle.com>, Ben Segall <bsegall@...gle.com>,
Peter Oskolkov <posk@...k.io>,
Joel Fernandes <joel@...lfernandes.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Andrei Vagin <avagin@...gle.com>,
Jim Newsome <jnewsome@...project.org>
Subject: Re: [RFC PATCH v0.1 7/9] sched/umcg: add UMCG server/worker API
(early RFC)
On Thu, May 20, 2021 at 11:36:12AM -0700, Peter Oskolkov wrote:
> Implement UMCG server/worker API.
>
> This is an early RFC patch - the code seems working, but
> more testing is needed. Gaps I plan to address before this
> is ready for a detailed review:
>
> - preemption/interrupt handling;
> - better documentation/comments;
> - tracing;
> - additional testing;
> - corner cases like abnormal process/task termination;
> - in some cases where I kill the task (umcg_segv), returning
> an error may be more appropriate.
>
> All in all, please focus more on the high-level approach
> and less on things like variable names, (doc) comments, or indentation.
>
> Signed-off-by: Peter Oskolkov <posk@...gle.com>
> ---
> include/linux/mm_types.h | 5 +
> include/linux/syscalls.h | 5 +
> kernel/fork.c | 11 +
> kernel/sched/core.c | 11 +
> kernel/sched/umcg.c | 764 ++++++++++++++++++++++++++++++++++++++-
> kernel/sched/umcg.h | 54 +++
> mm/init-mm.c | 4 +
> 7 files changed, 845 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 6613b26a8894..5ca7b7d55775 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -562,6 +562,11 @@ struct mm_struct {
> #ifdef CONFIG_IOMMU_SUPPORT
> u32 pasid;
> #endif
> +
> +#ifdef CONFIG_UMCG
> + spinlock_t umcg_lock;
> + struct list_head umcg_groups;
> +#endif
> } __randomize_layout;
>
> /*
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index 15de3e34ccee..2781659daaf1 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -1059,6 +1059,11 @@ asmlinkage long umcg_wait(u32 flags, const struct __kernel_timespec __user *time
> asmlinkage long umcg_wake(u32 flags, u32 next_tid);
> asmlinkage long umcg_swap(u32 wake_flags, u32 next_tid, u32 wait_flags,
> const struct __kernel_timespec __user *timeout);
> +asmlinkage long umcg_create_group(u32 api_version, u64, flags);
> +asmlinkage long umcg_destroy_group(u32 group_id);
> +asmlinkage long umcg_poll_worker(u32 flags, struct umcg_task __user **ut);
> +asmlinkage long umcg_run_worker(u32 flags, u32 worker_tid,
> + struct umcg_task __user **ut);
>
> /*
> * Architecture-specific system calls
> diff --git a/kernel/fork.c b/kernel/fork.c
> index ace4631b5b54..3a2a7950df8e 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1026,6 +1026,10 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
> seqcount_init(&mm->write_protect_seq);
> mmap_init_lock(mm);
> INIT_LIST_HEAD(&mm->mmlist);
> +#ifdef CONFIG_UMCG
> + spin_lock_init(&mm->umcg_lock);
> + INIT_LIST_HEAD(&mm->umcg_groups);
> +#endif
> mm->core_state = NULL;
> mm_pgtables_bytes_init(mm);
> mm->map_count = 0;
> @@ -1102,6 +1106,13 @@ static inline void __mmput(struct mm_struct *mm)
> list_del(&mm->mmlist);
> spin_unlock(&mmlist_lock);
> }
> +#ifdef CONFIG_UMCG
> + if (!list_empty(&mm->umcg_groups)) {
> + spin_lock(&mm->umcg_lock);
> + list_del(&mm->umcg_groups);
I am not sure that I understand what is going on here. umsg_groups is
the head of a group list. list_del is usually called on list entries.
Should we enumirate all groups here and destroy them?
> + spin_unlock(&mm->umcg_lock);
> + }
> +#endif
> if (mm->binfmt)
> module_put(mm->binfmt->module);
> mmdrop(mm);
...
> +/**
> + * sys_umcg_create_group - create a UMCG group
> + * @api_version: Requested API version.
> + * @flags: Reserved.
> + *
> + * Return:
> + * >= 0 - the group ID
> + * -EOPNOTSUPP - @api_version is not supported
> + * -EINVAL - @flags is not valid
> + * -ENOMEM - not enough memory
> + */
> +SYSCALL_DEFINE2(umcg_create_group, u32, api_version, u64, flags)
> +{
> + int ret;
> + struct umcg_group *group;
> + struct umcg_group *list_entry;
> + struct mm_struct *mm = current->mm;
> +
> + if (flags)
> + return -EINVAL;
> +
> + if (__api_version(api_version))
> + return -EOPNOTSUPP;
> +
> + group = kzalloc(sizeof(struct umcg_group), GFP_KERNEL);
> + if (!group)
> + return -ENOMEM;
> +
> + spin_lock_init(&group->lock);
> + INIT_LIST_HEAD(&group->list);
> + INIT_LIST_HEAD(&group->waiters);
> + group->flags = flags;
> + group->api_version = api_version;
> +
> + spin_lock(&mm->umcg_lock);
> +
> + list_for_each_entry_rcu(list_entry, &mm->umcg_groups, list) {
> + if (list_entry->group_id >= group->group_id)
> + group->group_id = list_entry->group_id + 1;
> + }
pls take into account that we need to be able to save and restore umcg
groups from user-space. There is the CRIU project that allows to
checkpoint/restore processes.
> +
> + list_add_rcu(&mm->umcg_groups, &group->list);
I think it should be:
list_add_rcu(&group->list, &mm->umcg_groups);
> +
> + ret = group->group_id;
> + spin_unlock(&mm->umcg_lock);
> +
> + return ret;
> +}
> +
Thanks,
Andrei
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