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Fri, 20 Jun 2025 14:55:11 +0000 (UTC) Received: from [192.168.1.26] (pv-asmtp-me-k8s.p00.prod.me.com [17.56.9.36]) by outbound.pv.icloud.com (Postfix) with ESMTPSA id CFEE018029B7; Fri, 20 Jun 2025 14:53:55 +0000 (UTC) From: Zijun Hu Date: Fri, 20 Jun 2025 22:53:32 +0800 Subject: [PATCH RFC] char: misc: Enforce simple minor space division Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250620-rfc_miscdev-v1-1-fda25d502a37@oss.qualcomm.com> X-B4-Tracking: v=1; b=H4sIAOt1VWgC/02OQQrCMBREr1L+2kCTJjbpVvAAbkUkyf/RLNpqU osgvbuhiricGWbmvSBTipShq16QaI45jkMRfFOBv9rhQixi0SBqoeqtqFkK/tzH7JFm1mrtAtf OWYVQGrdEIT7XtSMc9js4fcxE90dZnr6Js5mYH/s+TuXJiFa4prVWBt14q4TDYDzfokLNHSJvl JRGwj9RV/14yuHKc7WJtUYiSaGMMqKbOZyW5Q1WH5z+4QAAAA== X-Change-ID: 20250620-rfc_miscdev-788bf18bba5d To: Arnd Bergmann , Greg Kroah-Hartman Cc: Zijun Hu , linux-kernel@vger.kernel.org, Zijun Hu X-Mailer: b4 0.14.2 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNjIwMDEwNSBTYWx0ZWRfXxFtq5C8afgfi VaeraoLBA7stuJN+2S4DnpUPJhnFA+FCBxQhdFcCMS8Odc6HAMWOo5HAWu8SARCoHJp+4HG1eUf JRaXE19ydMkDCaZhCl/H2NHNZroF2DQ9zNqYG5klDG7PULWNmMQa6Of66lA2WPWZe8HV56zYu6I dPoQrxOiPI4G7w4CPEb8H/AoBQaIrdzYOhDIvKfffrKe3qrkVNMqNTEa6gRzqeZmkGH1dXUYQxx aM5OeRILnCVT7nJXb6lZ/iwhAPGaACt+OpgoB9BBZs3TtnNbnoJmZyZXCsIhPnlpN+mmU1Ux8= X-Proofpoint-GUID: lx9Ek0pTvSeRj_tVpRQHKQI_NZLnX9sL X-Proofpoint-ORIG-GUID: lx9Ek0pTvSeRj_tVpRQHKQI_NZLnX9sL X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.0.736,FMLib:17.12.80.40 definitions=2025-06-20_06,2025-06-20_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 phishscore=0 spamscore=0 suspectscore=0 bulkscore=0 adultscore=0 mlxscore=0 malwarescore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.22.0-2506060001 definitions=main-2506200105 From: Zijun Hu Enforce simple minor space division related to macro MISC_DYNAMIC_MINOR defined as 255 currently: < 255 : Fixed minor codes =3D=3D 255 : Indicator to request dynamic minor code > 255 : Dynamic minor codes requested This enforcing division also solves misc_register() reentry issue below: // Suppose both static @dev_A and @dev_B want to request dynamic minors. @dev_A.minor(255) @dev_B.minor(255) // Register @dev_A then de-register it. @dev_A.minor(255) -> registered -> @dev_A.minor(500) -> de-registered -> @dev_A.minor(500) // Register @dev_B @dev_B.minor(255) -> registered -> @dev_B.minor(500) // Register @dev_A again @dev_A.minor(500) -> encounter -EBUSY error since @dev_B has got 500. Side effects: It will be refused to register device whose fixed minor > 255. Signed-off-by: Zijun Hu --- drivers/char/misc.c | 16 +++++++++++++--- include/linux/miscdevice.h | 8 ++++++++ 2 files changed, 21 insertions(+), 3 deletions(-) diff --git a/drivers/char/misc.c b/drivers/char/misc.c index e5ea36bbf6b3d1313eb35d3259617bf90c55727d..e6a5907bbf915b4dd64522ada30= 24ba163cb7aa3 100644 --- a/drivers/char/misc.c +++ b/drivers/char/misc.c @@ -132,7 +132,8 @@ static int misc_open(struct inode *inode, struct file *= file) break; } =20 - if (!new_fops) { + /* Only request module for fixed minor code */ + if (!new_fops && minor < MISC_DYNAMIC_MINOR) { mutex_unlock(&misc_mtx); request_module("char-major-%d-%d", MISC_MAJOR, minor); mutex_lock(&misc_mtx); @@ -144,10 +145,11 @@ static int misc_open(struct inode *inode, struct file= *file) new_fops =3D fops_get(iter->fops); break; } - if (!new_fops) - goto fail; } =20 + if (!new_fops) + goto fail; + /* * Place the miscdevice in the file's * private_data so it can be used by the @@ -210,6 +212,12 @@ int misc_register(struct miscdevice *misc) int err =3D 0; bool is_dynamic =3D (misc->minor =3D=3D MISC_DYNAMIC_MINOR); =20 + if (misc->minor > MISC_DYNAMIC_MINOR) { + pr_err("Invalid fixed minor code %d for misc char device '%s'\n", + misc->minor, misc->name); + return -EINVAL; + } + INIT_LIST_HEAD(&misc->list); =20 mutex_lock(&misc_mtx); @@ -282,6 +290,8 @@ void misc_deregister(struct miscdevice *misc) list_del(&misc->list); device_destroy(&misc_class, MKDEV(MISC_MAJOR, misc->minor)); misc_minor_free(misc->minor); + if (misc->minor > MISC_DYNAMIC_MINOR) + misc->minor =3D MISC_DYNAMIC_MINOR; mutex_unlock(&misc_mtx); } EXPORT_SYMBOL(misc_deregister); diff --git a/include/linux/miscdevice.h b/include/linux/miscdevice.h index 3e6deb00fc8535a7571f85489c74979e18385bad..9e19bce981f065ea612da0a330c= 529e9c044c996 100644 --- a/include/linux/miscdevice.h +++ b/include/linux/miscdevice.h @@ -71,6 +71,14 @@ #define USERIO_MINOR 240 #define VHOST_VSOCK_MINOR 241 #define RFKILL_MINOR 242 + +/* + * Misc char device minor code space division related to below macro: + * + * < 255 : Fixed minor codes + * =3D=3D 255 : Indicator to request dynamic minor code + * > 255 : Dynamic minor codes requested + */ #define MISC_DYNAMIC_MINOR 255 =20 struct miscdevice { --- base-commit: 19272b37aa4f83ca52bdf9c16d5d81bdd1354494 change-id: 20250620-rfc_miscdev-788bf18bba5d prerequisite-change-id: 20250620-fix_mischar-794de4259592:v1 prerequisite-patch-id: 775e6edc4107a26a1fa30fd36315e4862dbc0cde prerequisite-patch-id: e32024c7470a34eb019af4bf18c08f67c3589d7e prerequisite-patch-id: 70045b4ad94130f051c314339a58217baed9190a Best regards, --=20 Zijun Hu