Re: [PATCH 0/1] sparc64: unify thread stack sizing and add explicit 32KB stack

On Tue, 19 May 2026 00:57:54 -0700
Tony Rodriguez <[email protected]> wrote:

> This patch fixes a reproducible stack exhaustion issue on SPARC64
> that occurs during USB hub enumeration. This regression may have
> started sometime after kernel v6.12. With the default 16KB kernel
> stack, the following panic is triggered early in boot:
> 
>     [   25.528399] Call Trace:
>     [   25.528403] [<0000000000433cd4>] dump_stack+0x8/0x18
>     [   25.528419] [<00000000004297ac>] vpanic+0xdc/0x318
>     [   25.528429] [<0000000000429a0c>] panic+0x24/0x30
>     [   25.528436] [<0000000000be2280>] __schedule+0xa8/0x7bc
>     [   25.528445] [<0000000000be2b60>] schedule+0x24/0x4c
>     [   25.528452] [<0000000000be6970>] schedule_timeout+0xc8/0xe4
>     [   25.528459] [<0000000000be3318>] __wait_for_common+0x78/0xf0
>     [   25.528466] [<0000000000be3550>] wait_for_completion_timeout+0x1c/0x2c
>     [   25.528473] [<000000001005e2f4>] usb_start_wait_urb+0x68/0x128 [usbcore]
>     [   25.528502] [<000000001005e468>] usb_control_msg+0xb4/0xf8 [usbcore]
>     [   25.528518] [<0000000010051180>] set_port_feature+0x44/0x54 [usbcore]
>     [   25.528530] [<00000000100530f0>] hub_power_on+0xc8/0xe8 [usbcore]
>     [   25.528543] [<0000000010054fd8>] hub_activate+0x12c/0x644 [usbcore]
>     [   25.528557] [<0000000010059438>] hub_probe+0xdd4/0xeb0 [usbcore]
>     [   25.528570] [<0000000010062360>] usb_probe_interface+0x234/0x26c [usbcore]
>     [   25.528585] [<0000000000a10a40>] really_probe+0x1ac/0x3b0
> 
> This is caused by large SPARC64 trapframes, register-window spills,
> and deep call paths in usbcore. A 16KB stack is insufficient for
> this workload.

Increasing the stack size for all threads seems overkill.
That stack doesn't even look deep.
I suspect there are large on-stack buffers in there.

Unfortunately the traceback doesn't print the stack pointers making
debugging hard.

-- David

> 
> The new logic is:
> 
>     SPARC64:
>         THREAD_SIZE = 4 * PAGE_SIZE (32KB)
>         THREAD_SHIFT = PAGE_SHIFT + 2
>         THREAD_SIZE_ORDER = 2
> 
>     Non‑SPARC64 with PAGE_SHIFT == 13:
>         Retains the existing 16KB stack behavior
> 
>     Fallback:
>         Retains the existing 8KB stack behavior
> 
> Signed-off-by: Tony Rodriguez <[email protected]>
> 
> 
> Tony Rodriguez (1):
>   sparc64: unify thread stack sizing and add explicit 32KB stack
> 
>  arch/sparc/include/asm/thread_info_64.h | 28 ++++++++++++-------------
>  1 file changed, 14 insertions(+), 14 deletions(-)
> 
> --
> 2.53.0
> 
>