linux-kernel - Re: [PATCH] IB/umem: use tgid instead of pid in ib

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Message-ID: <20180504182302.zunfryk2czge5adx@ziepe.ca>
Date:   Fri, 4 May 2018 12:23:02 -0600
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     858585 jemmy <jemmy858585@...il.com>
Cc:     dledford@...hat.com, akpm@...ux-foundation.org,
        qing.huang@...cle.com, Leon Romanovsky <leon@...nel.org>,
        artemyko@...lanox.com, dan.j.williams@...el.com,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        adido@...lanox.com, Gal Shachaf <galsha@...lanox.com>,
        Aviad Yehezkel <aviadye@...lanox.com>,
        Lidong Chen <lidongchen@...cent.com>
Subject: Re: [PATCH] IB/umem: use tgid instead of pid in ib_umem structure

On Fri, May 04, 2018 at 04:51:15PM +0800, 858585 jemmy wrote:
> On Fri, May 4, 2018 at 11:14 AM, 858585 jemmy <jemmy858585@...il.com> wrote:
> > On Thu, May 3, 2018 at 11:33 PM, Jason Gunthorpe <jgg@...pe.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@...cent.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 think a different process should not have the permission to release ib_umem.
> so maybe the reason is not a different process?
> can ib_umem_release be invoked in interrupt context?

We plan to restore fork support and add some way to share MRs between
processes, so we must consider having a different process release the
umem than acquired it.

Jason