Re: [PATCH] IB/umem: use tgid instead of pid in ib_umem structure

From: Leon Romanovsky <leon@kernel.org>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Lidong Chen <jemmy858585@gmail.com>,
	dledford@redhat.com, akpm@linux-foundation.org,
	qing.huang@oracle.com, artemyko@mellanox.com,
	dan.j.williams@intel.com, linux-rdma@vger.kernel.org,
	linux-kernel@vger.kernel.org, adido@mellanox.com,
	galsha@mellanox.com, aviadye@mellanox.com,
	Lidong Chen <lidongchen@tencent.com>
Subject: Re: [PATCH] IB/umem: use tgid instead of pid in ib_umem structure
Date: Thu, 3 May 2018 21:12:35 +0300	[thread overview]
Message-ID: <20180503181235.GB4473@mtr-leonro.local> (raw)
In-Reply-To: <20180503153310.GA9738@ziepe.ca>

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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?

> 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".

Thanks

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