6.6-stable review patch. If anyone has any objections, please let me know.
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From: Thadeu Lima de Souza Cascardo cascardo@igalia.com
[ Upstream commit 31b636d2c41613e3bd36256a4bd53e9dacfa2677 ]
When this was first reported [1], the possibility of having sufficient number of dynamic misc devices was theoretical, in the case of dlm driver. In practice, its userspace never created more than one device.
What we know from commit ab760791c0cf ("char: misc: Increase the maximum number of dynamic misc devices to 1048448"), is that the miscdevice interface has been used for allocating more than the single-shot devices it was designed for. And it is not only coresight_tmc, but many other drivers are able to create multiple devices.
On systems like the ones described in the above commit, it is certain that the dynamic allocation will allocate certain reserved minor numbers, leading to failures when a later driver tries to claim its reserved number.
Instead of excluding the historically statically allocated range from dynamic allocation, restrict the latter to minors above 255. That also removes the need for DYNAMIC_MINORS and the convolution in allocating minor numbers, simplifying the code.
Since commit ab760791c0cf ("char: misc: Increase the maximum number of dynamic misc devices to 1048448") has been applied, such range is already possible. And given such devices already need to be dynamically created, there should be no systems where this might become a problem.
[1] https://lore.kernel.org/all/1257813017-28598-3-git-send-email-cascardo@holos...
Signed-off-by: Thadeu Lima de Souza Cascardo cascardo@igalia.com Link: https://lore.kernel.org/r/20250423-misc-dynrange-v4-1-133b5ae4ca18@igalia.co... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/char/misc.c | 28 +++++----------------------- 1 file changed, 5 insertions(+), 23 deletions(-)
diff --git a/drivers/char/misc.c b/drivers/char/misc.c index 792a1412faffe..8d8c4bcf07e1c 100644 --- a/drivers/char/misc.c +++ b/drivers/char/misc.c @@ -58,9 +58,8 @@ static LIST_HEAD(misc_list); static DEFINE_MUTEX(misc_mtx);
/* - * Assigned numbers, used for dynamic minors + * Assigned numbers. */ -#define DYNAMIC_MINORS 128 /* like dynamic majors */ static DEFINE_IDA(misc_minors_ida);
static int misc_minor_alloc(int minor) @@ -69,34 +68,17 @@ static int misc_minor_alloc(int minor)
if (minor == MISC_DYNAMIC_MINOR) { /* allocate free id */ - ret = ida_alloc_max(&misc_minors_ida, DYNAMIC_MINORS - 1, GFP_KERNEL); - if (ret >= 0) { - ret = DYNAMIC_MINORS - ret - 1; - } else { - ret = ida_alloc_range(&misc_minors_ida, MISC_DYNAMIC_MINOR + 1, - MINORMASK, GFP_KERNEL); - } + ret = ida_alloc_range(&misc_minors_ida, MISC_DYNAMIC_MINOR + 1, + MINORMASK, GFP_KERNEL); } else { - /* specific minor, check if it is in dynamic or misc dynamic range */ - if (minor < DYNAMIC_MINORS) { - minor = DYNAMIC_MINORS - minor - 1; - ret = ida_alloc_range(&misc_minors_ida, minor, minor, GFP_KERNEL); - } else if (minor > MISC_DYNAMIC_MINOR) { - ret = ida_alloc_range(&misc_minors_ida, minor, minor, GFP_KERNEL); - } else { - /* case of non-dynamic minors, no need to allocate id */ - ret = 0; - } + ret = ida_alloc_range(&misc_minors_ida, minor, minor, GFP_KERNEL); } return ret; }
static void misc_minor_free(int minor) { - if (minor < DYNAMIC_MINORS) - ida_free(&misc_minors_ida, DYNAMIC_MINORS - minor - 1); - else if (minor > MISC_DYNAMIC_MINOR) - ida_free(&misc_minors_ida, minor); + ida_free(&misc_minors_ida, minor); }
#ifdef CONFIG_PROC_FS