From d1b3b9c70e11cb4f40b4e41a4dc1503b9a3c0109 Mon Sep 17 00:00:00 2001 From: Ian Abbott Date: Mon, 27 Oct 2025 15:25:02 +0000 Subject: [PATCH] comedi: kcomedilib: Add loop checking variants of open and close Add `comedi_open_from(path, from)` and `comedi_close_from(dev, from)` as variants of the existing `comedi_from(path)` and `comedi_close(dev)`. The additional `from` parameter is a minor device number that tells the function that the COMEDI device is being opened or closed from another COMEDI device if the value is in the range [0, `COMEDI_NUM_BOARD_MINORS`-1]. In that case the function will refuse to open the device if it would lead to a chain of devices opening each other. (It will also impose a limit on the number of simultaneous opens from one device to another because we need to count those.) The new functions are intended to be used by the "comedi_bond" driver, which is the only driver that uses the existing `comedi_open()` and `comedi_close()` functions. The new functions will be used to avoid some possible deadlock situations. Replace the existing, exported `comedi_open()` and `comedi_close()` functions with inline wrapper functions that call the newly exported `comedi_open_from()` and `comedi_close_from()` functions. Signed-off-by: Ian Abbott Link: https://patch.msgid.link/20251027153748.4569-2-abbotti@mev.co.uk Signed-off-by: Greg Kroah-Hartman --- drivers/comedi/kcomedilib/kcomedilib_main.c | 120 +++++++++++++++++++- include/linux/comedi/comedilib.h | 34 +++++- 2 files changed, 147 insertions(+), 7 deletions(-) diff --git a/drivers/comedi/kcomedilib/kcomedilib_main.c b/drivers/comedi/kcomedilib/kcomedilib_main.c index 43fbe1a63b14f..baa9eaaf97d4c 100644 --- a/drivers/comedi/kcomedilib/kcomedilib_main.c +++ b/drivers/comedi/kcomedilib/kcomedilib_main.c @@ -15,6 +15,7 @@ #include #include #include +#include #include #include @@ -24,7 +25,104 @@ MODULE_AUTHOR("David Schleef "); MODULE_DESCRIPTION("Comedi kernel library"); MODULE_LICENSE("GPL"); -struct comedi_device *comedi_open(const char *filename) +static DEFINE_MUTEX(kcomedilib_to_from_lock); + +/* + * Row index is the "to" node, column index is the "from" node, element value + * is the number of links from the "from" node to the "to" node. + */ +static unsigned char + kcomedilib_to_from[COMEDI_NUM_BOARD_MINORS][COMEDI_NUM_BOARD_MINORS]; + +static bool kcomedilib_set_link_from_to(unsigned int from, unsigned int to) +{ + DECLARE_BITMAP(destinations[2], COMEDI_NUM_BOARD_MINORS); + unsigned int cur = 0; + bool okay = true; + + /* + * Allow "from" node to be out of range (no loop checking), + * but require "to" node to be in range. + */ + if (to >= COMEDI_NUM_BOARD_MINORS) + return false; + if (from >= COMEDI_NUM_BOARD_MINORS) + return true; + + /* + * Check that kcomedilib_to_from[to][from] can be made non-zero + * without creating a loop. + * + * Termination of the loop-testing code relies on the assumption that + * kcomedilib_to_from[][] does not contain any loops. + * + * Start with a set destinations set containing "from" as the only + * element and work backwards looking for loops. + */ + bitmap_zero(destinations[cur], COMEDI_NUM_BOARD_MINORS); + set_bit(from, destinations[cur]); + mutex_lock(&kcomedilib_to_from_lock); + do { + unsigned int next = 1 - cur; + unsigned int t = 0; + + if (test_bit(to, destinations[cur])) { + /* Loop detected. */ + okay = false; + break; + } + /* Create next set of destinations. */ + bitmap_zero(destinations[next], COMEDI_NUM_BOARD_MINORS); + while ((t = find_next_bit(destinations[cur], + COMEDI_NUM_BOARD_MINORS, + t)) < COMEDI_NUM_BOARD_MINORS) { + unsigned int f; + + for (f = 0; f < COMEDI_NUM_BOARD_MINORS; f++) { + if (kcomedilib_to_from[t][f]) + set_bit(f, destinations[next]); + } + t++; + } + cur = next; + } while (!bitmap_empty(destinations[cur], COMEDI_NUM_BOARD_MINORS)); + if (okay) { + /* Allow a maximum of 255 links from "from" to "to". */ + if (kcomedilib_to_from[to][from] < 255) + kcomedilib_to_from[to][from]++; + else + okay = false; + } + mutex_unlock(&kcomedilib_to_from_lock); + return okay; +} + +static void kcomedilib_clear_link_from_to(unsigned int from, unsigned int to) +{ + if (to < COMEDI_NUM_BOARD_MINORS && from < COMEDI_NUM_BOARD_MINORS) { + mutex_lock(&kcomedilib_to_from_lock); + if (kcomedilib_to_from[to][from]) + kcomedilib_to_from[to][from]--; + mutex_unlock(&kcomedilib_to_from_lock); + } +} + +/** + * comedi_open_from() - Open a COMEDI device from the kernel with loop checks + * @filename: Fake pathname of the form "/dev/comediN". + * @from: Device number it is being opened from (if in range). + * + * Converts @filename to a COMEDI device number and "opens" it if it exists + * and is attached to a low-level COMEDI driver. + * + * If @from is in range, refuse to open the device if doing so would form a + * loop of devices opening each other. There is also a limit of 255 on the + * number of concurrent opens from one device to another. + * + * Return: A pointer to the COMEDI device on success. + * Return %NULL on failure. + */ +struct comedi_device *comedi_open_from(const char *filename, int from) { struct comedi_device *dev, *retval = NULL; unsigned int minor; @@ -43,7 +141,7 @@ struct comedi_device *comedi_open(const char *filename) return NULL; down_read(&dev->attach_lock); - if (dev->attached) + if (dev->attached && kcomedilib_set_link_from_to(from, minor)) retval = dev; else retval = NULL; @@ -54,14 +152,26 @@ struct comedi_device *comedi_open(const char *filename) return retval; } -EXPORT_SYMBOL_GPL(comedi_open); +EXPORT_SYMBOL_GPL(comedi_open_from); -int comedi_close(struct comedi_device *dev) +/** + * comedi_close_from() - Close a COMEDI device from the kernel with loop checks + * @dev: COMEDI device. + * @from: Device number it was opened from (if in range). + * + * Closes a COMEDI device previously opened by comedi_open_from(). + * + * If @from is in range, it should be match the one used by comedi_open_from(). + * + * Returns: 0 + */ +int comedi_close_from(struct comedi_device *dev, int from) { + kcomedilib_clear_link_from_to(from, dev->minor); comedi_dev_put(dev); return 0; } -EXPORT_SYMBOL_GPL(comedi_close); +EXPORT_SYMBOL_GPL(comedi_close_from); static int comedi_do_insn(struct comedi_device *dev, struct comedi_insn *insn, diff --git a/include/linux/comedi/comedilib.h b/include/linux/comedi/comedilib.h index 0223c9cd9215b..1f2b22b383cc5 100644 --- a/include/linux/comedi/comedilib.h +++ b/include/linux/comedi/comedilib.h @@ -10,8 +10,38 @@ #ifndef _LINUX_COMEDILIB_H #define _LINUX_COMEDILIB_H -struct comedi_device *comedi_open(const char *path); -int comedi_close(struct comedi_device *dev); +struct comedi_device *comedi_open_from(const char *path, int from); + +/** + * comedi_open() - Open a COMEDI device from the kernel + * @filename: Fake pathname of the form "/dev/comediN". + * + * Converts @filename to a COMEDI device number and "opens" it if it exists + * and is attached to a low-level COMEDI driver. + * + * Return: A pointer to the COMEDI device on success. + * Return %NULL on failure. + */ +static inline struct comedi_device *comedi_open(const char *path) +{ + return comedi_open_from(path, -1); +} + +int comedi_close_from(struct comedi_device *dev, int from); + +/** + * comedi_close() - Close a COMEDI device from the kernel + * @dev: COMEDI device. + * + * Closes a COMEDI device previously opened by comedi_open(). + * + * Returns: 0 + */ +static inline int comedi_close(struct comedi_device *dev) +{ + return comedi_close_from(dev, -1); +} + int comedi_dio_get_config(struct comedi_device *dev, unsigned int subdev, unsigned int chan, unsigned int *io); int comedi_dio_config(struct comedi_device *dev, unsigned int subdev, -- 2.47.3