From: Johannes Stezenbach <js@linuxtv.org>
To: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Cc: "Linux Media Mailing List" <linux-media@vger.kernel.org>,
"Mauro Carvalho Chehab" <mchehab@infradead.org>,
"Andy Lutomirski" <luto@amacapital.net>,
"Jiri Kosina" <jikos@kernel.org>,
"Patrick Boettcher" <patrick.boettcher@posteo.de>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"Andy Lutomirski" <luto@kernel.org>,
"Michael Krufky" <mkrufky@linuxtv.org>,
"Mauro Carvalho Chehab" <mchehab@kernel.org>,
"Jörg Otte" <jrg.otte@gmail.com>
Subject: Re: [PATCH v2 02/31] cinergyT2-core: don't do DMA on stack
Date: Sat, 15 Oct 2016 22:54:49 +0200 [thread overview]
Message-ID: <20161015205449.pagb3a7nld7q6al4@linuxtv.org> (raw)
In-Reply-To: <1220fd764d747f153c240e14812e1d2045e59b4e.1476179975.git.mchehab@s-opensource.com>
On Tue, Oct 11, 2016 at 07:09:17AM -0300, Mauro Carvalho Chehab wrote:
> --- a/drivers/media/usb/dvb-usb/cinergyT2-core.c
> +++ b/drivers/media/usb/dvb-usb/cinergyT2-core.c
> @@ -41,6 +41,8 @@ DVB_DEFINE_MOD_OPT_ADAPTER_NR(adapter_nr);
>
> struct cinergyt2_state {
> u8 rc_counter;
> + unsigned char data[64];
> + struct mutex data_mutex;
> };
Sometimes my thinking is slow but it just occured to me
that this creates a potential issue with cache line sharing.
On an architecture which manages cache coherence in software
(ARM, MIPS etc.) a write to e.g. rc_counter in this example
would dirty the cache line, and a later writeback from the
cache could overwrite parts of data[] which was received via DMA.
In contrast, if the DMA buffer is allocated seperately via
kmalloc it is guaranteed to be safe wrt cache line sharing.
(see bottom of Documentation/DMA-API-HOWTO.txt).
But of course DMA on stack also had the same issue
and no one ever noticed so it's apparently not critical...
Johannes
next prev parent reply other threads:[~2016-10-15 20:55 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-11 10:09 [PATCH v2 00/31] Don't use stack for DMA transers on media usb drivers Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 01/31] af9005: don't do DMA on stack Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 02/31] cinergyT2-core: " Mauro Carvalho Chehab
2016-10-15 20:54 ` Johannes Stezenbach [this message]
2016-10-17 17:12 ` Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 03/31] cinergyT2-core: handle error code on RC query Mauro Carvalho Chehab
2016-10-12 2:13 ` [PATCH v2.1 " Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 04/31] cinergyT2-fe: cache stats at cinergyt2_fe_read_status() Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 05/31] cinergyT2-fe: don't do DMA on stack Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 06/31] cxusb: " Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 07/31] dib0700: be sure that dib0700_ctrl_rd() users can do DMA Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 08/31] dib0700_core: don't use stack on I2C reads Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 09/31] dibusb: don't do DMA on stack Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 10/31] dibusb: handle error code on RC query Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 11/31] digitv: don't do DMA on stack Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 12/31] dtt200u-fe: don't keep waiting for lock at set_frontend() Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 13/31] dtt200u-fe: don't do DMA on stack Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 14/31] dtt200u-fe: handle errors on USB control messages Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 15/31] dtt200u: don't do DMA on stack Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 16/31] dtt200u: handle USB control message errors Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 17/31] dtv5100: don't do DMA on stack Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 18/31] gp8psk: " Mauro Carvalho Chehab
2016-11-06 19:51 ` VDR User
2016-11-07 11:29 ` Johannes Stezenbach
2016-11-07 12:53 ` Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 19/31] gp8psk: don't go past the buffer size Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 20/31] nova-t-usb2: don't do DMA on stack Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 21/31] pctv452e: " Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 22/31] pctv452e: don't call BUG_ON() on non-fatal error Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 23/31] technisat-usb2: use DMA buffers for I2C transfers Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 24/31] dvb-usb: warn if return value for USB read/write routines is not checked Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 25/31] nova-t-usb2: handle error code on RC query Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 26/31] dw2102: return error if su3000_power_ctrl() fails Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 27/31] digitv: handle error code on RC query Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 28/31] cpia2_usb: don't use stack for DMA Mauro Carvalho Chehab
2016-10-11 22:56 ` Kosuke Tatsukawa
2016-10-12 2:18 ` [PATCH v2 .1 " Mauro Carvalho Chehab
2016-10-12 2:19 ` [PATCH v2 " Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 29/31] s2255drv: " Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 30/31] stk-webcam: " Mauro Carvalho Chehab
2016-10-11 10:09 ` [PATCH v2 31/31] flexcop-usb: " Mauro Carvalho Chehab
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