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Message-ID: <e999d699-b764-5a58-c1ec-6f53e0e8521d@hisilicon.com>
Date: Mon, 2 Sep 2024 21:32:10 +0800
From: Junxian Huang <huangjunxian6@...ilicon.com>
To: Leon Romanovsky <leon@...nel.org>, <jgg@...pe.ca>
CC: <linux-rdma@...r.kernel.org>, <linuxarm@...wei.com>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 for-next 1/2] RDMA/core: Provide
rdma_user_mmap_disassociate() to disassociate mmap pages
On 2024/9/2 14:57, Leon Romanovsky wrote:
> On Wed, Aug 28, 2024 at 02:46:04PM +0800, Junxian Huang wrote:
>> From: Chengchang Tang <tangchengchang@...wei.com>
>>
>> Provide a new api rdma_user_mmap_disassociate() for drivers to
>> disassociate mmap pages for a device.
>>
>> Signed-off-by: Chengchang Tang <tangchengchang@...wei.com>
>> Signed-off-by: Junxian Huang <huangjunxian6@...ilicon.com>
>> ---
>> drivers/infiniband/core/uverbs.h | 3 ++
>> drivers/infiniband/core/uverbs_main.c | 45 +++++++++++++++++++++++++--
>> include/rdma/ib_verbs.h | 8 +++++
>> 3 files changed, 54 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/infiniband/core/uverbs.h b/drivers/infiniband/core/uverbs.h
>> index 821d93c8f712..0999d27cb1c9 100644
>> --- a/drivers/infiniband/core/uverbs.h
>> +++ b/drivers/infiniband/core/uverbs.h
>> @@ -160,6 +160,9 @@ struct ib_uverbs_file {
>> struct page *disassociate_page;
>>
>> struct xarray idr;
>> +
>> + struct mutex disassociation_lock;
>> + atomic_t disassociated;
>> };
>>
>> struct ib_uverbs_event {
>> diff --git a/drivers/infiniband/core/uverbs_main.c b/drivers/infiniband/core/uverbs_main.c
>> index bc099287de9a..589f27c09a2e 100644
>> --- a/drivers/infiniband/core/uverbs_main.c
>> +++ b/drivers/infiniband/core/uverbs_main.c
>> @@ -76,6 +76,7 @@ static dev_t dynamic_uverbs_dev;
>> static DEFINE_IDA(uverbs_ida);
>> static int ib_uverbs_add_one(struct ib_device *device);
>> static void ib_uverbs_remove_one(struct ib_device *device, void *client_data);
>> +static struct ib_client uverbs_client;
>>
>> static char *uverbs_devnode(const struct device *dev, umode_t *mode)
>> {
>> @@ -217,6 +218,7 @@ void ib_uverbs_release_file(struct kref *ref)
>>
>> if (file->disassociate_page)
>> __free_pages(file->disassociate_page, 0);
>> + mutex_destroy(&file->disassociation_lock);
>> mutex_destroy(&file->umap_lock);
>> mutex_destroy(&file->ucontext_lock);
>> kfree(file);
>> @@ -700,6 +702,12 @@ static int ib_uverbs_mmap(struct file *filp, struct vm_area_struct *vma)
>> ret = PTR_ERR(ucontext);
>> goto out;
>> }
>> +
>> + if (atomic_read(&file->disassociated)) {
>
> I don't see any of the newly introduced locks here. If it is
> intentional, it needs to be documented.
>
<...>
>> + ret = -EPERM;
>> + goto out;
>> + }
>> +
>> vma->vm_ops = &rdma_umap_ops;
>> ret = ucontext->device->ops.mmap(ucontext, vma);
>> out:
>> @@ -726,7 +734,7 @@ static void rdma_umap_open(struct vm_area_struct *vma)
>> /*
>> * Disassociation already completed, the VMA should already be zapped.
>> */
>> - if (!ufile->ucontext)
>> + if (!ufile->ucontext || atomic_read(&ufile->disassociated))
>> goto out_unlock;
>>
>> priv = kzalloc(sizeof(*priv), GFP_KERNEL);
>> @@ -822,6 +830,8 @@ void uverbs_user_mmap_disassociate(struct ib_uverbs_file *ufile)
>> struct rdma_umap_priv *priv, *next_priv;
>>
>> lockdep_assert_held(&ufile->hw_destroy_rwsem);
>> + mutex_lock(&ufile->disassociation_lock);
>> + atomic_set(&ufile->disassociated, 1);
>
> Why do you use atomic_t and not regular bool?
>
The original thought was that ib_uverbs_mmap() reads ufile->disassociated while
uverbs_user_mmap_disassociate() writes it, and there might be a racing. We tried
to use atomic_t to avoid racing without adding locks.
But I looked into the code again and now I think ufile->disassociated is not
sufficient to deal with the racing like this:
ib_uverbs_mmap() uverbs_user_mmap_disassociate()
---------------- ------------------------------
atomic_read(&file->disassociated) == 0
atomic_set(&ufile->disassociated, 1)
all mmaps from the list are zapped
ucontext->device->ops.mmap(ucontext, vma)
rdma_user_mmap_io()
rdma_umap_priv_init() adds a new mmap to the list
So we may still need a lock, and ufile->disassociated can be bool now, something like:
@@ -700,9 +702,17 @@ static int ib_uverbs_mmap(struct file *filp, struct vm_area_struct *vma)
ret = PTR_ERR(ucontext);
goto out;
}
+
+ mutex_lock(&file->disassociation_lock);
+ if (file->disassociated) {
+ ret = -EPERM;
+ goto out;
+ }
+
vma->vm_ops = &rdma_umap_ops;
ret = ucontext->device->ops.mmap(ucontext, vma);
out:
+ mutex_unlock(&file->disassociation_lock);
srcu_read_unlock(&file->device->disassociate_srcu, srcu_key);
return ret;
}
Similar changes on rdma_umap_open():
@@ -723,10 +733,12 @@ static void rdma_umap_open(struct vm_area_struct *vma)
/* We are racing with disassociation */
if (!down_read_trylock(&ufile->hw_destroy_rwsem))
goto out_zap;
+
+ mutex_lock(&ufile->disassociation_lock);
/*
* Disassociation already completed, the VMA should already be zapped.
*/
- if (!ufile->ucontext)
+ if (!ufile->ucontext || ufile->disassociated)
goto out_unlock;
priv = kzalloc(sizeof(*priv), GFP_KERNEL);
@@ -734,10 +746,12 @@ static void rdma_umap_open(struct vm_area_struct *vma)
goto out_unlock;
rdma_umap_priv_init(priv, vma, opriv->entry);
+ mutex_unlock(&ufile->disassociation_lock);
up_read(&ufile->hw_destroy_rwsem);
return;
out_unlock:
+ mutex_unlock(&ufile->disassociation_lock);
up_read(&ufile->hw_destroy_rwsem);
out_zap:
/*
>>
>> while (1) {
>> struct mm_struct *mm = NULL;
>> @@ -847,8 +857,10 @@ void uverbs_user_mmap_disassociate(struct ib_uverbs_file *ufile)
>> break;
>> }
>> mutex_unlock(&ufile->umap_lock);
>> - if (!mm)
>> + if (!mm) {
>> + mutex_unlock(&ufile->disassociation_lock);
>> return;
>> + }
>>
>> /*
>> * The umap_lock is nested under mmap_lock since it used within
>> @@ -878,8 +890,34 @@ void uverbs_user_mmap_disassociate(struct ib_uverbs_file *ufile)
>> mmap_read_unlock(mm);
>> mmput(mm);
>> }
>> +
>> + mutex_unlock(&ufile->disassociation_lock);
>> }
>>
>> +/**
>> + * rdma_user_mmap_disassociate() - Revoke mmaps for a device
>> + * @device: device to revoke
>> + *
>> + * This function should be called by drivers that need to disable mmaps for the
>> + * device, for instance because it is going to be reset.
>> + */
>> +void rdma_user_mmap_disassociate(struct ib_device *device)
>> +{
>> + struct ib_uverbs_device *uverbs_dev =
>> + ib_get_client_data(device, &uverbs_client);
>> + struct ib_uverbs_file *ufile;
>> +
>> + mutex_lock(&uverbs_dev->lists_mutex);
>> + list_for_each_entry(ufile, &uverbs_dev->uverbs_file_list, list) {
>> + down_read(&ufile->hw_destroy_rwsem);
>
> I personally don't understand this locking scheme at all. I see newly
> introduced locks mixed together some old locks.
>
We must hold the rwsem because of the lockdep. The newly introduced lock
is also needed to prevent the racing that one thread is calling
rdma_user_mmap_disassociate(), while the other thread is calling
ib_uverbs_mmap() or rdma_umap_open().
Thanks,
Junxian
> Jason, do you agree with this proposed locking scheme?
>
> Thanks
>
>> + if (ufile->ucontext && !atomic_read(&ufile->disassociated))
>> + uverbs_user_mmap_disassociate(ufile);
>> + up_read(&ufile->hw_destroy_rwsem);
>> + }
>> + mutex_unlock(&uverbs_dev->lists_mutex);
>> +}
>> +EXPORT_SYMBOL(rdma_user_mmap_disassociate);
>> +
>> /*
>> * ib_uverbs_open() does not need the BKL:
>> *
>> @@ -949,6 +987,9 @@ static int ib_uverbs_open(struct inode *inode, struct file *filp)
>> mutex_init(&file->umap_lock);
>> INIT_LIST_HEAD(&file->umaps);
>>
>> + mutex_init(&file->disassociation_lock);
>> + atomic_set(&file->disassociated, 0);
>> +
>> filp->private_data = file;
>> list_add_tail(&file->list, &dev->uverbs_file_list);
>> mutex_unlock(&dev->lists_mutex);
>> diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
>> index a1dcf812d787..09b80c8253e2 100644
>> --- a/include/rdma/ib_verbs.h
>> +++ b/include/rdma/ib_verbs.h
>> @@ -2948,6 +2948,14 @@ int rdma_user_mmap_entry_insert_range(struct ib_ucontext *ucontext,
>> size_t length, u32 min_pgoff,
>> u32 max_pgoff);
>>
>> +#if IS_ENABLED(CONFIG_INFINIBAND_USER_ACCESS)
>> +void rdma_user_mmap_disassociate(struct ib_device *device);
>> +#else
>> +static inline void rdma_user_mmap_disassociate(struct ib_device *device)
>> +{
>> +}
>> +#endif
>> +
>> static inline int
>> rdma_user_mmap_entry_insert_exact(struct ib_ucontext *ucontext,
>> struct rdma_user_mmap_entry *entry,
>> --
>> 2.33.0
>>
>>
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