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SubjectRe: [PATCH] IB/umem: use tgid instead of pid in ib_umem structure
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> 在 2018年5月4日,21:39,Leon Romanovsky <leon@kernel.org> 写道:
>
>> On Fri, May 04, 2018 at 04:32:38PM +0800, 858585 jemmy wrote:
>>> On Fri, May 4, 2018 at 6:01 AM, Jason Gunthorpe <jgg@ziepe.ca> wrote:
>>>> On Thu, May 03, 2018 at 09:43:01PM +0300, Leon Romanovsky wrote:
>>>>> On Thu, May 03, 2018 at 12:26:56PM -0600, Jason Gunthorpe wrote:
>>>>>> On Thu, May 03, 2018 at 09:12:35PM +0300, Leon Romanovsky wrote:
>>>>>>> On Thu, May 03, 2018 at 09:33:10AM -0600, Jason Gunthorpe wrote:
>>>>>>>> On Thu, May 03, 2018 at 10:04:34PM +0800, Lidong Chen wrote:
>>>>>>>> The userspace may invoke ibv_reg_mr and ibv_dereg_mr by different threads.
>>>>>>>> If when ibv_dereg_mr invoke and the thread which invoked ibv_reg_mr has
>>>>>>>> exited, get_pid_task will return NULL, ib_umem_release does not decrease
>>>>>>>> mm->pinned_vm. This patch fixes it by use tgid.
>>>>>>>>
>>>>>>>> Signed-off-by: Lidong Chen <lidongchen@tencent.com>
>>>>>>>> drivers/infiniband/core/umem.c | 12 ++++++------
>>>>>>>> include/rdma/ib_umem.h | 2 +-
>>>>>>>> 2 files changed, 7 insertions(+), 7 deletions(-)
>>>>>>>
>>>>>>> Why are we even using a struct pid for this? Does anyone know?
>>>>>>>
>>>>>>
>>>>>> Can it be related to "fork" support?
>>>>>
>>>>> Not sure..
>>>>>
>>>>> Ideally we want to hold the struct mm, but we can't hold it long
>>>>> term, so pid is a surrogate for that.
>>>>>
>>>>>>> I'm surprised that struct task isn't held in the struct ib_umem..
>>>>>>>
>>>>>>
>>>>>> I think that this code can be removed and all accesses to mm_struct can
>>>>>> be done with "current->mm".
>>>>>
>>>>> That sounds wrong for fork support, as the mm used in destroy MUST
>>>>> exactly match the mm used in create..
>>>>>
>>>>> How does this accounting work in fork anyhow?
>>>>
>>>> We are not supporting fork, so this is why I proposed to remove it.
>>>
>>> Er, the new kabi certainly can call reg and dereg across a fork
>>
>> what is the expect behavior after fork?
>> I write a test code, the dereg just return EACCES in the child
>> process. and have no effect.
>
> Did you do reg/dereg over write() interface? If yes, this is expected
> behaviour of "not-supported fork()". A couple of months/years ago, your
> test program would work, but we closed this option due to security
> constraints.

the parent process call ibv_reg_mr, and the child process call ibv_dereg_mr.

If fork is not supported now, so use tgid to get mm structure is fine for multithread.

>
> Thanks
>
>>
>>>
>>> Jason
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