From 49db08c358873af11ba3c25401de88156fa5d365 Mon Sep 17 00:00:00 2001 From: Linus Walleij Date: Fri, 19 Feb 2016 15:36:07 +0100 Subject: chrdev: emit a warning when we go below dynamic major range Currently a dynamically allocated character device major is taken from 254 and downward. This mechanism is used for RTC, IIO and a few other subsystems. The kernel currently has no check prevening these dynamic allocations from eating into the assigned numbers at 233 and downward. In a recent test it was reported that so many dynamic device majors were used on a test server, that the major number for infiniband (231) was stolen. This occurred when allocating a new major number for GPIO chips. The error messages from the kernel were not helpful. (See: https://lkml.org/lkml/2016/2/14/124) This patch adds a defined lower limit of the dynamic major allocation region will henceforth emit a warning if we start to eat into the assigned numbers. It does not do any semantic changes and will not change the kernels behaviour: numbers will still continue to be stolen, but we will know from dmesg what is going on. This also updates the Documentation/devices.txt to clearly reflect that we are using this range of major numbers for dynamic allocation. Reported-by: Ying Huang Cc: Linus Torvalds Cc: Greg Kroah-Hartman Cc: Alan Cox Cc: Arnd Bergmann Signed-off-by: Linus Walleij Signed-off-by: Greg Kroah-Hartman --- Documentation/devices.txt | 6 +++--- fs/char_dev.c | 4 ++++ include/linux/fs.h | 2 ++ 3 files changed, 9 insertions(+), 3 deletions(-) diff --git a/Documentation/devices.txt b/Documentation/devices.txt index 87b4c5e82d39..0a3588a9798d 100644 --- a/Documentation/devices.txt +++ b/Documentation/devices.txt @@ -3099,9 +3099,9 @@ Your cooperation is appreciated. 129 = /dev/ipath_sma Device used by Subnet Management Agent 130 = /dev/ipath_diag Device used by diagnostics programs -234-239 UNASSIGNED - -240-254 char LOCAL/EXPERIMENTAL USE +234-254 char RESERVED FOR DYNAMIC ASSIGNMENT + Character devices that request a dynamic allocation of major number will + take numbers starting from 254 and downward. 240-254 block LOCAL/EXPERIMENTAL USE Allocated for local/experimental use. For devices not diff --git a/fs/char_dev.c b/fs/char_dev.c index 24b142569ca9..687471dc04a0 100644 --- a/fs/char_dev.c +++ b/fs/char_dev.c @@ -91,6 +91,10 @@ __register_chrdev_region(unsigned int major, unsigned int baseminor, break; } + if (i < CHRDEV_MAJOR_DYN_END) + pr_warn("CHRDEV \"%s\" major number %d goes below the dynamic allocation range", + name, i); + if (i == 0) { ret = -EBUSY; goto out; diff --git a/include/linux/fs.h b/include/linux/fs.h index 14a97194b34b..60082be96de8 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2385,6 +2385,8 @@ static inline void bd_unlink_disk_holder(struct block_device *bdev, /* fs/char_dev.c */ #define CHRDEV_MAJOR_HASH_SIZE 255 +/* Marks the bottom of the first segment of free char majors */ +#define CHRDEV_MAJOR_DYN_END 234 extern int alloc_chrdev_region(dev_t *, unsigned, unsigned, const char *); extern int register_chrdev_region(dev_t, unsigned, const char *); extern int __register_chrdev(unsigned int major, unsigned int baseminor, -- cgit v1.2.3-59-g8ed1b