From a5d31a3f81c6fb13b381951bf6163444c0257e8b Mon Sep 17 00:00:00 2001 From: Logan Gunthorpe Date: Thu, 15 Jun 2017 14:05:20 -0600 Subject: [PATCH] char_dev: extend dynamic allocation of majors into a higher range We've run into problems with running out of dynamicly assign char device majors particullarly on automated test systems with all-yes-configs. Roughly 40 dynamic assignments can be made with such kernels at this time while space is reserved for only 20. Currently, the kernel only prints a warning when dynamic allocation overflows the reserved region. And when this happens drivers that have fixed assignments can randomly fail depending on the order of initialization of other drivers. Thus, adding a new char device can cause unexpected failures in completely unrelated parts of the kernel. This patch solves the problem by extending dynamic major number allocations down from 511 once the 234-254 region fills up. Fixed majors already exist above 255 so the infrastructure to support high number majors is already in place. The patch reserves an additional 128 major numbers which should hopefully last us a while. Kernels that don't require more than 20 dynamic majors assigned (which is pretty typical) should not be affected by this change. Signed-off-by: Logan Gunthorpe Cc: Linus Torvalds Cc: Alan Cox Cc: Arnd Bergmann Cc: Linus Walleij Link: https://lkml.org/lkml/2017/6/4/107 Signed-off-by: Greg Kroah-Hartman --- Documentation/admin-guide/devices.txt | 5 ++++ fs/char_dev.c | 41 ++++++++++++++++++--------- include/linux/fs.h | 4 +++ 3 files changed, 37 insertions(+), 13 deletions(-) diff --git a/Documentation/admin-guide/devices.txt b/Documentation/admin-guide/devices.txt index 6b71852dadc2..4ec843123cc3 100644 --- a/Documentation/admin-guide/devices.txt +++ b/Documentation/admin-guide/devices.txt @@ -3081,3 +3081,8 @@ 1 = /dev/osd1 Second OSD Device ... 255 = /dev/osd255 256th OSD Device + + 384-511 char RESERVED FOR DYNAMIC ASSIGNMENT + Character devices that request a dynamic allocation of major + number will take numbers starting from 511 and downward, + once the 234-254 range is full. diff --git a/fs/char_dev.c b/fs/char_dev.c index fb8507f521b2..c9d18362e89d 100644 --- a/fs/char_dev.c +++ b/fs/char_dev.c @@ -59,6 +59,29 @@ void chrdev_show(struct seq_file *f, off_t offset) #endif /* CONFIG_PROC_FS */ +static int find_dynamic_major(void) +{ + int i; + struct char_device_struct *cd; + + for (i = ARRAY_SIZE(chrdevs)-1; i > CHRDEV_MAJOR_DYN_END; i--) { + if (chrdevs[i] == NULL) + return i; + } + + for (i = CHRDEV_MAJOR_DYN_EXT_START; + i > CHRDEV_MAJOR_DYN_EXT_END; i--) { + for (cd = chrdevs[major_to_index(i)]; cd; cd = cd->next) + if (cd->major == i) + break; + + if (cd == NULL || cd->major != i) + return i; + } + + return -EBUSY; +} + /* * Register a single major with a specified minor range. * @@ -84,22 +107,14 @@ __register_chrdev_region(unsigned int major, unsigned int baseminor, mutex_lock(&chrdevs_lock); - /* temporary */ if (major == 0) { - for (i = ARRAY_SIZE(chrdevs)-1; i > 0; i--) { - if (chrdevs[i] == NULL) - break; - } - - if (i < CHRDEV_MAJOR_DYN_END) - pr_warn("CHRDEV \"%s\" major number %d goes below the dynamic allocation range\n", - name, i); - - if (i == 0) { - ret = -EBUSY; + ret = find_dynamic_major(); + if (ret < 0) { + pr_err("CHRDEV \"%s\" dynamic allocation region is full\n", + name); goto out; } - major = i; + major = ret; } cd->major = major; diff --git a/include/linux/fs.h b/include/linux/fs.h index 7b5d6816542b..1773dcf1e318 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2473,6 +2473,10 @@ static inline void bd_unlink_disk_holder(struct block_device *bdev, #define CHRDEV_MAJOR_HASH_SIZE 255 /* Marks the bottom of the first segment of free char majors */ #define CHRDEV_MAJOR_DYN_END 234 +/* Marks the top and bottom of the second segment of free char majors */ +#define CHRDEV_MAJOR_DYN_EXT_START 511 +#define CHRDEV_MAJOR_DYN_EXT_END 384 + 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, -- 2.20.1