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mx.google.com; dkim=pass header.i=@microsoft.com header.s=selector1 header.b=XRLkHBvh; spf=pass (google.com: domain of alexander.levin@microsoft.com designates 104.47.40.130 as permitted sender) smtp.mailfrom=Alexander.Levin@microsoft.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=microsoft.com Authentication-Results: mx.google.com; dkim=pass header.i=@microsoft.com header.s=selector1 header.b=XRLkHBvh; spf=pass (google.com: domain of alexander.levin@microsoft.com designates 104.47.40.130 as permitted sender) smtp.mailfrom=Alexander.Levin@microsoft.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=microsoft.com From: Sasha Levin To: "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" CC: Vignesh R , Greg Kroah-Hartman , Sasha Levin Subject: [PATCH AUTOSEL for 4.9 071/281] serial: 8250: omap: Disable DMA for console UART Thread-Topic: [PATCH AUTOSEL for 4.9 071/281] serial: 8250: omap: Disable DMA for console UART Thread-Index: AQHTv5s5IyeRPHtT+UCiE2JZOS/duA== Date: Mon, 19 Mar 2018 15:59:12 +0000 Message-ID: <20180319155742.13731-71-alexander.levin@microsoft.com> References: <20180319155742.13731-1-alexander.levin@microsoft.com> In-Reply-To: <20180319155742.13731-1-alexander.levin@microsoft.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [52.168.54.252] x-ms-publictraffictype: Email x-microsoft-exchange-diagnostics: 1;DM5PR2101MB0869;7:JnhVo2Jb9g0ZPRpyrdpgNQofNbWgqb1Tjy6v2ONbrJxZnUB/PbuR/1EZGG32wWuggneSMxHpdf568e0k+3tnwaiCAZYTCMRTUUy/s3gSHehBgR04jsIAelKzHrILhytkXH1qpPZAXIl2GzEtvPYCm+7O46nZdfVEKSGVYPjAMGwNAYmh+jvUq8HsDactfzoGpmxSkh7/dV4e+hAWtpHrCsXwRmI6v8VDK4VaUvUvFKA6sYHp/0qMzM+/pb48EF3z;20:cOSA5VJDNlsvyRi9jCbd/+qHFLRHRXWnWnjoc9hw9tCUQMZw3o6LDHTcxfTsTRs7Xib6QDRdP3Mlv0Um4kRHwArz0QhGGlkaEZ7R2G8mxsrQES4Lzga/GciY2VjOrHk8f14syccH/NaRoF/C/94U1XxDDCFV533UfMPa8SNJvDE= x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: d1620f79-337d-4892-32d6-08d58db277d4 x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(4652020)(48565401081)(5600026)(4604075)(3008032)(4534165)(4627221)(201703031133081)(201702281549075)(2017052603328)(7193020);SRVR:DM5PR2101MB0869; 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x-microsoft-antispam-message-info: t5QHycriguEftdfL02ghbCqjH9FhHYHnCdTnrTUzrLXClLYc8IgtKA1kwnvTrmzQDQXySn75v0kGzaIB5c537FL/5mPxMjW41DeI/zEUX7d08RsYZ/72qHHiUBnu5eLV0MDbNY1oHW3S+z2XGcXzLXJbm0prJB11V3b68XjIVqyVhH+AzPtThgp1V/89qusiNukUHDJxXTnRKKj3qLabCrJQLBNqFDDcCWOVIxsvOt7ikXf+cFzbaRw3Dg2aQ3KaR6J1WTGFQzXSeai/RVpAzLaiEbrawbH1xk20Jg0w8G/KHyB42PSt7XjboAg33A7BWb2QG0dY444znI5WOhop6w== spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-Network-Message-Id: d1620f79-337d-4892-32d6-08d58db277d4 X-MS-Exchange-CrossTenant-originalarrivaltime: 19 Mar 2018 15:59:12.7153 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM5PR2101MB0869 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1595382380868186672?= X-GMAIL-MSGID: =?utf-8?q?1595382380868186672?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: From: Vignesh R [ Upstream commit 84b40e3b57eef1417479c00490dd4c9f6e5ffdbc ] Kernel always writes log messages to console via serial8250_console_write()->serial8250_console_putchar() which directly accesses UART_TX register _without_ using DMA. But, if other processes like systemd using same UART port, then these writes are handled by a different code flow using 8250_omap driver where there is provision to use DMA. It seems that it is possible that both DMA and CPU might simultaneously put data to UART FIFO and lead to potential loss of data due to FIFO overflow and weird data corruption. This happens when both kernel console and userspace tries to write simultaneously to the same UART port. Therefore, disable DMA on kernel console port to avoid potential race between CPU and DMA. Signed-off-by: Vignesh R Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- drivers/tty/serial/8250/8250_omap.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/= 8250_omap.c index da31159a03ec..e8b34f16ba2c 100644 --- a/drivers/tty/serial/8250/8250_omap.c +++ b/drivers/tty/serial/8250/8250_omap.c @@ -613,6 +613,10 @@ static int omap_8250_startup(struct uart_port *port) up->lsr_saved_flags =3D 0; up->msr_saved_flags =3D 0; =20 + /* Disable DMA for console UART */ + if (uart_console(port)) + up->dma =3D NULL; + if (up->dma) { ret =3D serial8250_request_dma(up); if (ret) { --=20 2.14.1