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[88.187.86.199]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4606f26f309sm48890784f8f.14.2026.06.17.05.01.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 17 Jun 2026 05:01:16 -0700 (PDT) Message-ID: Date: Wed, 17 Jun 2026 14:01:15 +0200 Precedence: bulk X-Mailing-List: linux-mips@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 5/6] serial: sb1250-duart: Switch to spinlock protection for shared resource Content-Language: en-US To: "Maciej W. Rozycki" , Thomas Bogendoerfer , Greg Kroah-Hartman , Jiri Slaby Cc: Elena Reshetova , David Windsor , Kees Cook , Hans Liljestrand , linux-mips@vger.kernel.org, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org References: From: =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Proofpoint-GUID: aARX3fuJPnS8K5plRkD3tY1tRK3wSGIm X-Authority-Analysis: v=2.4 cv=JufBas4C c=1 sm=1 tr=0 ts=6a328c8e cx=c_pps a=z9lCQkyTxNhZyzAvolXo/A==:117 a=4s3hRJSeHn4rkQlkrse1kQ==:17 a=IkcTkHD0fZMA:10 a=FelO9ux0wxsA:10 a=M51BFTxLslgA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=YMgV9FUhrdKAYTUUvYB2:22 a=BcPKCTjPAAAA:8 a=EUspDBNiAAAA:8 a=EbunRdXsnukT5RqbSTkA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=EyFUmsFV_t8cxB2kMr4A:22 a=MNXww67FyIVnWKX2fotq:22 X-Proofpoint-ORIG-GUID: aARX3fuJPnS8K5plRkD3tY1tRK3wSGIm X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNjE3MDExNCBTYWx0ZWRfXwW8I1+Ayru/c ewbMwkolURo/hpDNpqFCnqK41iOBzu/wmu+EaZHGX/P9AA37ANAlcL8IKwJ5czUZco+tm83ftQd hVt6iJsTVB6def5FHisICKPZDUSwJEcFwPjbtHdwlykZP+h920x2SZ8OKcnWc1eD1V3DiUyCUqq KoP1RjuPkXxbIZd/IjAG5gO2vzWv/j/kGvOvWnuDG7NBq6k5qbAdDub8SJLrFpw4IXAqVdj3v/M 3x63yGwxuOhgEqzve4o6kbcETrVxCZEJ0UPjyDO5Qub3/RblGDoyeHBs4v7gboQ6hKm6yQWqt/j +yilbAN80FyyyRCunz4A98cXwyaDVvJC+VLajSia7i3NbMO9794QQOBqYV+7jSvqkYOTAd9Wsb8 N/YRijvTQNuF5JVICNhEqwgdpqDgrkuHbDPSOC/CDs7ADllR5EiqaA+kqUJJilHIaUuCszNf0kL 9hQowAb3aLPmN3xVTLA== X-Proofpoint-Spam-Info: AW1haW4tMjYwNjE3MDExNCBTYWx0ZWRfX0W/MDlxIE4Ch +2Wgov+1lB2/75sriuGvU7mXiBjZGsTKBK3mRrcDIuUS8/2ChOZM/NPm1e8uszSMhbkCAAEPx3/ opyUJwVwbH/gPspq8hvx2MzWocvkLd8= X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-06-17_01,2026-06-16_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 clxscore=1015 adultscore=0 priorityscore=1501 impostorscore=0 spamscore=0 bulkscore=0 lowpriorityscore=0 suspectscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2606170114 On 25/5/26 01:12, Maciej W. Rozycki wrote: > The control register block is shared between DUART channels and so its > resource has to be requested by the first channel claimed and released > by the last one dropped. > > It is currently handled with an atomic counter, which however does not > protect against a situation where request_mem_region() has failed, but > another CPU has seen the map guard nonzero and refrained from calling > this function for another channel where it should have (and likely also > fail). This parallel execution scenario can in principle be arranged > via the TIOCSSERIAL ioctl. > > Switch to using an ordinary counter then and spinlock protection for the > counter updates along with the corresponding resource request/release > calls, so that the case described above is covered. > > Fixes: b45d52797432 ("sb1250-duart.c: SB1250 DUART serial support") > Signed-off-by: Maciej W. Rozycki > --- > New change in v2. > --- > drivers/tty/serial/sb1250-duart.c | 28 ++++++++++++++++++---------- > 1 file changed, 18 insertions(+), 10 deletions(-) Reviewed-by: Philippe Mathieu-Daudé