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

[David Laight <david.laight.linux@gmail.com>]

On Tue, 19 May 2026 16:57:04 -0700
Tony Rodriguez <unixpro1970@gmail.com> wrote:

> On 5/19/26 3:02 AM, David Laight wrote:
> > On Tue, 19 May 2026 00:57:54 -0700
> > Tony Rodriguez <unixpro1970@gmail.com> 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  
> 
> Hi David. Any specific grub command line keywords and values, and 
> functions you recommend for debugging this?  I would be happy to share 
> Trace Calls, etc. so it is easier to reconfirm and zero in on the issue. 

Without the stack offsets from the dump, look at the stack frame sizes
for the functions in that traceback.
I suspect there are too many that get near the compile-time threshold.

-- David

> -- Tony
> 
> >> 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 <unixpro1970@gmail.com>
> >>
> >>
> >> 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
> >>
> >>  
>