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From:   Jason Gunthorpe <jgg@mellanox.com>
To:     Michal Hocko <mhocko@kernel.org>
CC:     Stable tree <stable@vger.kernel.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Jann Horn <jannh@google.com>, Oleg Nesterov <oleg@redhat.com>,
        Peter Xu <peterx@redhat.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Joel Fernandes <joel@joelfernandes.org>
Subject: Re: [PATCH stable 4.4 v2] coredump: fix race condition between
 mmget_not_zero()/get_task_mm() and core dumping
Thread-Topic: [PATCH stable 4.4 v2] coredump: fix race condition between
 mmget_not_zero()/get_task_mm() and core dumping
Thread-Index: AQHVH2CnxFwP6PSr9UaRiZwKrYERwKaU6mGAgAAFSwA=
Date:   Mon, 10 Jun 2019 14:17:25 +0000
Message-ID: <20190610141720.GB18446@mellanox.com>
References: <20190604094953.26688-1-mhocko@kernel.org>
 <20190610074635.2319-1-mhocko@kernel.org>
 <20190610135823.GI30967@dhcp22.suse.cz>
In-Reply-To: <20190610135823.GI30967@dhcp22.suse.cz>
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On Mon, Jun 10, 2019 at 03:58:23PM +0200, Michal Hocko wrote:
> Just a heads up. Ajay Kaher has noticed that mlx4 driver is missing the
> check in 4.14 [1] and 4.4 seems to have the same problem. I will wait
> for more review before reposting v3. The incremental diff is:
>=20
> diff --git a/drivers/infiniband/hw/mlx4/main.c b/drivers/infiniband/hw/ml=
x4/main.c
> index 67c4c73343d4..6968154a073e 100644
> +++ b/drivers/infiniband/hw/mlx4/main.c
> @@ -1042,6 +1042,8 @@ static void mlx4_ib_disassociate_ucontext(struct ib=
_ucontext *ibcontext)
>  	 * mlx4_ib_vma_close().
>  	 */
>  	down_write(&owning_mm->mmap_sem);
> +	if (!mmget_still_valid(owning_mm))
> +		goto skip_mm;
>  	for (i =3D 0; i < HW_BAR_COUNT; i++) {
>  		vma =3D context->hw_bar_info[i].vma;
>  		if (!vma)
> @@ -1061,6 +1063,7 @@ static void mlx4_ib_disassociate_ucontext(struct ib=
_ucontext *ibcontext)
>  		context->hw_bar_info[i].vma->vm_ops =3D NULL;
>  	}
> =20
> +skip_mm:
>  	up_write(&owning_mm->mmap_sem);
>  	mmput(owning_mm);
>  	put_task_struct(owning_process);

Looks OK to me

Jason