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SubjectRe: [PATCH] IB/umem: use tgid instead of pid in ib_umem structure
On Thu, May 3, 2018 at 11:33 PM, Jason Gunthorpe <jgg@ziepe.ca> 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?

commit 87773dd56d5405ac28119fcfadacefd35877c18f add pid in ib_umem structure.

and the comment has such information:
Later a different process with a different mm_struct than the one that
allocated the ib_umem struct
ends up releasing it which results in decrementing the new processes
mm->pinned_vm count past
zero and wrapping.

>
> I'm surprised that struct task isn't held in the struct ib_umem..
>
> Is group_leader really OK and always guarenteed to return the same
> struct mm?? For some reason I have this recollection that the leader
> can change under some situation..
>
>> diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
>> index 9a4e899..8813ba5 100644
>> --- a/drivers/infiniband/core/umem.c
>> +++ b/drivers/infiniband/core/umem.c
>> @@ -119,7 +119,7 @@ struct ib_umem *ib_umem_get(struct ib_ucontext *context, unsigned long addr,
>> umem->length = size;
>> umem->address = addr;
>> umem->page_shift = PAGE_SHIFT;
>> - umem->pid = get_task_pid(current, PIDTYPE_PID);
>> + umem->tgid = get_task_pid(current->group_leader, PIDTYPE_PID);
>> /*
>> * We ask for writable memory if any of the following
>> * access flags are set. "Local write" and "remote write"
>> @@ -132,7 +132,7 @@ struct ib_umem *ib_umem_get(struct ib_ucontext *context, unsigned long addr,
>> IB_ACCESS_REMOTE_ATOMIC | IB_ACCESS_MW_BIND));
>>
>> if (access & IB_ACCESS_ON_DEMAND) {
>> - put_pid(umem->pid);
>> + put_pid(umem->tgid);
>> ret = ib_umem_odp_get(context, umem, access);
>> if (ret) {
>> kfree(umem);
>> @@ -148,7 +148,7 @@ struct ib_umem *ib_umem_get(struct ib_ucontext *context, unsigned long addr,
>>
>> page_list = (struct page **) __get_free_page(GFP_KERNEL);
>> if (!page_list) {
>> - put_pid(umem->pid);
>> + put_pid(umem->tgid);
>> kfree(umem);
>> return ERR_PTR(-ENOMEM);
>> }
>> @@ -231,7 +231,7 @@ struct ib_umem *ib_umem_get(struct ib_ucontext *context, unsigned long addr,
>> if (ret < 0) {
>> if (need_release)
>> __ib_umem_release(context->device, umem, 0);
>> - put_pid(umem->pid);
>> + put_pid(umem->tgid);
>> kfree(umem);
>> } else
>> current->mm->pinned_vm = locked;
>> @@ -274,8 +274,8 @@ void ib_umem_release(struct ib_umem *umem)
>>
>> __ib_umem_release(umem->context->device, umem, 1);
>>
>> - task = get_pid_task(umem->pid, PIDTYPE_PID);
>> - put_pid(umem->pid);
>> + task = get_pid_task(umem->tgid, PIDTYPE_PID);
>> + put_pid(umem->tgid);
>> if (!task)
>> goto out;
>> mm = get_task_mm(task);
>> diff --git a/include/rdma/ib_umem.h b/include/rdma/ib_umem.h
>> index 23159dd..2398849 100644
>> --- a/include/rdma/ib_umem.h
>> +++ b/include/rdma/ib_umem.h
>> @@ -48,7 +48,7 @@ struct ib_umem {
>> int writable;
>> int hugetlb;
>> struct work_struct work;
>> - struct pid *pid;
>> + struct pid *tgid;
>> struct mm_struct *mm;
>> unsigned long diff;
>> struct ib_umem_odp *odp_data;
>> --
>> 1.8.3.1
>>

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