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 <logang@deltatee.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Alan Cox <alan@linux.intel.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Linus Walleij <linus.walleij@linaro.org> Link: https://lkml.org/lkml/2017/6/4/107 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -3081,3 +3081,8 @@
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1 = /dev/osd1 Second OSD Device
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...
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255 = /dev/osd255 256th OSD Device
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384-511 char RESERVED FOR DYNAMIC ASSIGNMENT
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Character devices that request a dynamic allocation of major
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number will take numbers starting from 511 and downward,
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once the 234-254 range is full.
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@ -59,6 +59,29 @@ void chrdev_show(struct seq_file *f, off_t offset)
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#endif /* CONFIG_PROC_FS */
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static int find_dynamic_major(void)
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{
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int i;
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struct char_device_struct *cd;
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for (i = ARRAY_SIZE(chrdevs)-1; i > CHRDEV_MAJOR_DYN_END; i--) {
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if (chrdevs[i] == NULL)
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return i;
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}
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for (i = CHRDEV_MAJOR_DYN_EXT_START;
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i > CHRDEV_MAJOR_DYN_EXT_END; i--) {
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for (cd = chrdevs[major_to_index(i)]; cd; cd = cd->next)
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if (cd->major == i)
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break;
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if (cd == NULL || cd->major != i)
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return i;
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}
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return -EBUSY;
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}
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/*
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* Register a single major with a specified minor range.
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*
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@ -84,22 +107,14 @@ __register_chrdev_region(unsigned int major, unsigned int baseminor,
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mutex_lock(&chrdevs_lock);
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/* temporary */
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if (major == 0) {
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for (i = ARRAY_SIZE(chrdevs)-1; i > 0; i--) {
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if (chrdevs[i] == NULL)
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break;
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}
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if (i < CHRDEV_MAJOR_DYN_END)
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pr_warn("CHRDEV \"%s\" major number %d goes below the dynamic allocation range\n",
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name, i);
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if (i == 0) {
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ret = -EBUSY;
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ret = find_dynamic_major();
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if (ret < 0) {
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pr_err("CHRDEV \"%s\" dynamic allocation region is full\n",
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name);
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goto out;
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}
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major = i;
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major = ret;
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}
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cd->major = major;
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@ -2473,6 +2473,10 @@ static inline void bd_unlink_disk_holder(struct block_device *bdev,
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#define CHRDEV_MAJOR_HASH_SIZE 255
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/* Marks the bottom of the first segment of free char majors */
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#define CHRDEV_MAJOR_DYN_END 234
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/* Marks the top and bottom of the second segment of free char majors */
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#define CHRDEV_MAJOR_DYN_EXT_START 511
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#define CHRDEV_MAJOR_DYN_EXT_END 384
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extern int alloc_chrdev_region(dev_t *, unsigned, unsigned, const char *);
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extern int register_chrdev_region(dev_t, unsigned, const char *);
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extern int __register_chrdev(unsigned int major, unsigned int baseminor,
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