linux-kernel - Re: [PATCH 4/4] drivers/misc/sgi-gru: fix dereference of ERR

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Date:	Wed, 2 Sep 2015 10:03:04 -0500
From:	Dimitri Sivanich <sivanich@....com>
To:	Sudip Mukherjee <sudipm.mukherjee@...il.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] drivers/misc/sgi-gru: fix dereference of ERR_PTR

On Wed, Sep 02, 2015 at 04:54:58PM +0530, Sudip Mukherjee wrote:
> gru_alloc_gts() can fail and it can return ERR_PTR(errvalue). We should
> not dereference it if it has returned error. And incase it has returned
> error then just downgrade the write lock and exit.
> 

Not sure about this, because gru_load_kernel_context is expected to complete
with a loaded context.  Since most if not all error possibilities are out of
memory conditions, it might be better to loop (with an msleep(1)) and wait
for forward progress, similar to the while loop in this function.

> Signed-off-by: Sudip Mukherjee <sudip@...torindia.org>
> ---
>  drivers/misc/sgi-gru/grukservices.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/misc/sgi-gru/grukservices.c b/drivers/misc/sgi-gru/grukservices.c
> index a6fd773..369f7fe 100644
> --- a/drivers/misc/sgi-gru/grukservices.c
> +++ b/drivers/misc/sgi-gru/grukservices.c
> @@ -161,6 +161,8 @@ static void gru_load_kernel_context(struct gru_blade_state *bs, int blade_id)
>  
>  	if (!bs->bs_kgts) {
>  		bs->bs_kgts = gru_alloc_gts(NULL, 0, 0, 0, 0, 0);
> +		if (IS_ERR(bs->bs_kgts))
> +			goto err_gru_alloc_gts;
>  		bs->bs_kgts->ts_user_blade_id = blade_id;
>  	}
>  	kgts = bs->bs_kgts;
> @@ -184,6 +186,7 @@ static void gru_load_kernel_context(struct gru_blade_state *bs, int blade_id)
>  		bs->kernel_cb = get_gseg_base_address_cb(vaddr, ctxnum, 0);
>  		bs->kernel_dsr = get_gseg_base_address_ds(vaddr, ctxnum, 0);
>  	}
> +err_gru_alloc_gts:
>  	downgrade_write(&bs->bs_kgts_sema);
>  }
>  
> -- 
> 1.9.1
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