Re: misc_deregister() throwing warning in ida_free()

[Greg Kroah-Hartman]

On Mon, Sep 16, 2024 at 06:56:18PM +0530, Vimal Agrawal wrote:
> Hi Scott/ Greg and all,
> 
> We recently upgraded kernel from 6.1 to 6.6.49 and started seeing
> following WARNING during misc_deregister():
> 
> ------------[ cut here ]------------
> 
> WARNING: CPU: 0 PID: 159 at lib/idr.c:525 ida_free+0x3e0/0x41f
> ida_free called for id=127 which is not allocated.
> <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
> Modules linked in: ust(O-) [last unloaded: fastpath_dummy(O)]
> CPU: 0 PID: 159 Comm: modprobe Tainted: G        W  O     N 6.6.49+ #11
> Stack:
> 818bfb70 6093f8d3 0000020d 61381660
> 61381630 60c1ee6a 00000001 60068c0f
> 818bfbb0 60983ee6 60983e5c 61381680
> Call Trace:
> [<60973831>] ? _printk+0x0/0xc2
> [<6004b2e6>] show_stack+0x35c/0x382
> [<6093f8d3>] ? dump_stack_print_info+0x1af/0x1ec
> [<60068c0f>] ? um_set_signals+0x0/0x43
> [<60983ee6>] dump_stack_lvl+0x8a/0xa9
> [<60983e5c>] ? dump_stack_lvl+0x0/0xa9
> [<60068c0f>] ? um_set_signals+0x0/0x43
> [<60983f32>] dump_stack+0x2d/0x35
> [<60983f05>] ? dump_stack+0x0/0x35
> [<6007aad8>] __warn+0x20c/0x294
> [<60068c0f>] ? um_set_signals+0x0/0x43
> [<60971d98>] warn_slowpath_fmt+0x164/0x189
> [<60222128>] ? __update_cpu_freelist_fast+0x96/0xbc
> [<60971c34>] ? warn_slowpath_fmt+0x0/0x189
> [<6022d2fe>] ? __kmem_cache_free+0x16a/0x1be
> [<60068c4a>] ? um_set_signals+0x3b/0x43
> [<60941eb4>] ida_free+0x3e0/0x41f
> [<605ac993>] misc_minor_free+0x3e/0xbc
> [<605acb82>] misc_deregister+0x171/0x1b3
> [<81aa7af2>] ustdev_exit+0xa8/0xc1 [ust]
> 
> basic code of calling misc_register()/misc_register() is following:
> 
> static struct miscdevice ust_dev = {
>         0,
>         "ustdev",
>         &ustdev_ops,
> };

Nit, use named-identifiers pleaase so we know what is being set and what
isn't.

> int ustdev_init(void)
> {
>         misc_register(&ust_dev);
>         return 0;

This can be just one line, you are ignoring if misc_register() fails :(

> }
> 
> void ustdev_exit(void)
> {
>         misc_deregister(&ust_dev);
> }
> 
> Note that this was working fine without any warning earlier on kernel 6.1.
> 
> I suspect it is due to
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=v6.6.51&id=ab760791c0cfbb1d7a668f46a135264f56c8f018.
> It seems misc_register() is not calling any ida_allocxxx() api for
> static minor value of 0 but misc_deregister() for the same is calling
> ida_free() and hence ida_free() is warning in our case.
> 
> Please let me know if I am missing something or some of our
> assumptions are not valid anymore in newer kernel versions.

Can you submit a patch that works for you to resolve this issue?

thanks,

greg k-h