linux-kernel - RE: [PATCH] rapidio: avoid GFP_KERNEL in atomic context in riocm_send

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Date:   Wed, 14 Sep 2016 19:48:07 +0000
From:   "Bounine, Alexandre" <Alexandre.Bounine@....com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Khoroshilov <khoroshilov@...ras.ru>,
        Matt Porter <mporter@...nel.crashing.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ldv-project@...uxtesting.org" <ldv-project@...uxtesting.org>
Subject: RE: [PATCH] rapidio: avoid GFP_KERNEL in atomic context in
 riocm_send_close()

On Sunday, Sep 11, 2016 12:45 AM Andrew Morton <akpm@...ux-foundation.org: wrote:
> 
> On Fri, 9 Sep 2016 21:22:14 -0700 Andrew Morton <akpm@...ux-
> foundation.org> wrote:
> 
> > Why not just make `hdr' a local?  It isn't very large and the code
> > becomes smaller and faster.
> 
> Actually, doing it this way saves some code size and is faster:
>

Using local 'hdr' will cause a reference to an illegal memory in case when
"close" request is placed into priority queue due to lack of free buffer
descriptors in low-level HW driver. This can happen during high intensity
messaging traffic - when riocm_send_close() is called from riocm_ch_close().

I will rework rio_cm_shutdown() to take riocm_send_close() call out of spin-lock
protected code area.
 
> 
> From: Andrew Morton <akpm@...ux-foundation.org>
> Subject: drivers/rapidio/rio_cm.c: avoid GFP_KERNEL in atomic context
> 
> riocm_send_close() is called from rio_cm_shutdown() under
> spin_lock_bh(idr_lock), but riocm_send_close() uses a GFP_KERNEL
> allocation.
> 
> Fix this by making local `hdr' a local variable rather than obtaining
> it
> via kmalloc().
> 
> Found by Linux Driver Verification project (linuxtesting.org).
> 
> Link: http://lkml.kernel.org/r/1473453815-15914-1-git-send-email-
> khoroshilov@...ras.ru
> Reported-by: Alexey Khoroshilov <khoroshilov@...ras.ru>
> Cc: Alexandre Bounine <alexandre.bounine@....com>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> ---
> 
>  drivers/rapidio/rio_cm.c |   38 ++++++++++++++++---------------------
>  1 file changed, 17 insertions(+), 21 deletions(-)
> 
> diff -puN drivers/rapidio/rio_cm.c~drivers-rapidio-rio_cmc-avoid-
> gfp_kernel-in-atomic-context drivers/rapidio/rio_cm.c
> --- a/drivers/rapidio/rio_cm.c~drivers-rapidio-rio_cmc-avoid-
> gfp_kernel-in-atomic-context
> +++ a/drivers/rapidio/rio_cm.c
> @@ -1395,38 +1395,34 @@ static void riocm_ch_free(struct kref *r
>  	complete(&ch->comp_close);
>  }
> 
> +/*
> + * Send CH_CLOSE notification to the remote RapidIO device
> + */
>  static int riocm_send_close(struct rio_channel *ch)
>  {
> -	struct rio_ch_chan_hdr *hdr;
>  	int ret;
> -
> -	/*
> -	 * Send CH_CLOSE notification to the remote RapidIO device
> -	 */
> -
> -	hdr = kzalloc(sizeof(*hdr), GFP_KERNEL);
> -	if (hdr == NULL)
> -		return -ENOMEM;
> -
> -	hdr->bhdr.src_id = htonl(ch->loc_destid);
> -	hdr->bhdr.dst_id = htonl(ch->rem_destid);
> -	hdr->bhdr.src_mbox = cmbox;
> -	hdr->bhdr.dst_mbox = cmbox;
> -	hdr->bhdr.type = RIO_CM_CHAN;
> -	hdr->ch_op = CM_CONN_CLOSE;
> -	hdr->dst_ch = htons(ch->rem_channel);
> -	hdr->src_ch = htons(ch->id);
> +	struct rio_ch_chan_hdr hdr = {
> +		.bhdr = {
> +			.src_id = htonl(ch->loc_destid),
> +			.dst_id = htonl(ch->rem_destid),
> +			.src_mbox = cmbox,
> +			.dst_mbox = cmbox,
> +			.type = RIO_CM_CHAN,
> +		},
> +		.ch_op = CM_CONN_CLOSE,
> +		.dst_ch = htons(ch->rem_channel),
> +		.src_ch = htons(ch->id),
> +	};
> 
>  	/* ATTN: the function call below relies on the fact that
> underlying
>  	 * add_outb_message() routine copies TX data into its internal
> transfer
>  	 * buffer. Needs to be reviewed if switched to direct buffer
> mode.
>  	 */
> -	ret = riocm_post_send(ch->cmdev, ch->rdev, hdr, sizeof(*hdr));
> +	ret = riocm_post_send(ch->cmdev, ch->rdev, &hdr, sizeof(hdr));
> 
>  	if (ret == -EBUSY && !riocm_queue_req(ch->cmdev, ch->rdev,
> -					      hdr, sizeof(*hdr)))
> +					      &hdr, sizeof(hdr)))
>  		return 0;
> -	kfree(hdr);
> 
>  	if (ret)
>  		riocm_error("ch(%d) send CLOSE failed (ret=%d)", ch->id,
> ret);
> _
> 
>