[PATCH v2] sparc64: increase kernel thread stack size to 32K

[PATCH v2] sparc64: increase kernel thread stack size to 32K

[Stian Halseth]

From: Tony Rodriguez <unixpro1970@gmail.com>

Kernel stacks on sparc64 are 16K and this is no longer enough:
several machines (SPARC T5-2 among them) panic early in boot during
USB hub enumeration with "corrupted stack end detected inside
scheduler". sparc has not been converted to THREAD_INFO_IN_TASK, so
thread_info sits at the bottom of the kernel stack and a marginal
overflow corrupts it first; CONFIG_SCHED_STACK_END_CHECK then fires
from __schedule long after the deep path has unwound, which is why
the reported backtraces look shallow.

Measurements with CONFIG_STACK_TRACER on an UltraSPARC T4-1 show the
problem is frame count, not any single large frame. The high-water
mark of an ordinary successful boot is 12616 of 16384 bytes (77%),
reached in hub_probe() with a printk console flush and then a timer
interrupt (which runs on the task stack, and whose scheduler tick
performs load balancing and IPI delivery) stacked on top. Of the 66
frames in that path the largest is 408 bytes, and ~85% of them are
176-224 bytes - at or just above the SPARC V9 ABI minimum frame
(128-byte register window save area plus 48-byte argument save
area). An equivalent call chain on x86-64 costs roughly a third of
the stack, so a 16K stack on sparc64 provides far less effective
call depth than on other 64-bit architectures.

Double THREAD_SIZE to 32K (four 8K pages). The PAGE_SHIFT
conditionals are dropped: sparc64 only supports 8K base pages, so
the other branches were dead code. Kernel stacks become order-2
allocations; sparc64 has no VMAP_STACK, but stacks are allocated
once per thread and the trade against boot-time panics is a good
one.

Link: https://lore.kernel.org/all/20260519075809.8993-1-unixpro1970@gmail.com/
Signed-off-by: Tony Rodriguez <unixpro1970@gmail.com>
[stian: reduced the diff to the THREAD_* defines, measured stack
 usage with CONFIG_STACK_TRACER and rewrote the changelog]
Signed-off-by: Stian Halseth <stian@itx.no>
---
v2:
 - drop the CONFIG_SPARC64 / PAGE_SHIFT conditional chain from v1;
   thread_info_64.h is only built on sparc64 and only 8K pages are
   supported, so define the three constants unconditionally
 - replace the panic backtrace in the changelog with stack tracer
   measurements answering David Laight's review comments:
   https://lore.kernel.org/all/20260520144104.618c75ca@pumpkin/
 - retitled from "unify thread stack sizing and add explicit 32KB
   stack"; the sizing logic for other configurations is unchanged

Tested on an UltraSPARC T4-1, booted with the stack tracer armed
("stacktrace") before and after this patch. The boot high-water mark
is 12616 bytes on both kernels - the worst path (hub_probe with a
printk and a timer interrupt on top) is deterministic - i.e. 77% of
the 16K stack before, 38% of the 32K stack after. DEBUG_STACK_USAGE
agrees: the peak boot-time task shows 9208 bytes left of 16K before
vs 25592 bytes left of 32K after (7176 bytes used in both).

 arch/sparc/include/asm/thread_info_64.h | 15 +++------------
 1 file changed, 3 insertions(+), 12 deletions(-)

diff --git a/arch/sparc/include/asm/thread_info_64.h b/arch/sparc/include/asm/thread_info_64.h
--- a/arch/sparc/include/asm/thread_info_64.h
+++ b/arch/sparc/include/asm/thread_info_64.h
@@ -99,13 +99,8 @@
 #define FAULT_CODE_BLKCOMMIT	0x10	/* Use blk-commit ASI in copy_page */
 #define	FAULT_CODE_BAD_RA	0x20	/* Bad RA for sun4v		   */
 
-#if PAGE_SHIFT == 13
-#define THREAD_SIZE (2*PAGE_SIZE)
-#define THREAD_SHIFT (PAGE_SHIFT + 1)
-#else /* PAGE_SHIFT == 13 */
-#define THREAD_SIZE PAGE_SIZE
-#define THREAD_SHIFT PAGE_SHIFT
-#endif /* PAGE_SHIFT == 13 */
+#define THREAD_SIZE (4 * PAGE_SIZE)
+#define THREAD_SHIFT (PAGE_SHIFT + 2)
 
 /*
  * macros/functions for gaining access to the thread information structure
@@ -128,11 +123,7 @@
 #endif
 
 /* thread information allocation */
-#if PAGE_SHIFT == 13
-#define THREAD_SIZE_ORDER	1
-#else /* PAGE_SHIFT == 13 */
-#define THREAD_SIZE_ORDER	0
-#endif /* PAGE_SHIFT == 13 */
+#define THREAD_SIZE_ORDER	2
 
 #define __thread_flag_byte_ptr(ti)	\
 	((unsigned char *)(&((ti)->flags)))
--
2.53.0

Re: [PATCH v2] sparc64: increase kernel thread stack size to 32K

[Tony Rodriguez]

Hi Stian,

Thanks for following up regarding this, I am currently busy with other 
tasks.  Back in May/June 2026, I also mentioned the following to Andreas:

The combined stack usage is already very close to the 32K limit. If you 
need an immediate workaround, increasing the stack to 64 K may be the 
better option. That should provide enough headroom to avoid the stack 
overflow panics we are seeing.  As of kernel 7.1, I haven't noticed any 
panics using a 32K stack, but once again a stack size that is so close 
to the 32K boundary is a concern. But once again, sparc64 definitely 
crashes with a 16K stack.  The Nvidia/Mellonox mlx5 driver also 
allocates a big stack on sparc64, which pushes it to the 32K boundary.  
There may be other drivers that may do so as well.

The 64K stack is more ideal.

When I compile the kernel with -fstack-usage to generate .su files, on 
7.1 kerner, the static analysis shows small stack frames for all USB 
core functions.
For example:

hub_event:      2457 bytes  (static)
hub_activate:   1892 bytes  (static)
usb_control_msg: 1248 bytes (static)

However, my runtime stack tracing shows a dramatically different picture:

STACKTRACE: hub_event():entry: 31856 bytes used
STACKTRACE: hub_activate():entry: 31680 bytes used
STACKTRACE: usb_control_msg():entry: 30768 bytes used


PS - I have not tested a 64K stack yet, only 32K, and this is a heads-up 
recommendation.


Tony

On 8/31/26 10:29 AM, Stian Halseth wrote:
> From: Tony Rodriguez <unixpro1970@gmail.com>
>
> Kernel stacks on sparc64 are 16K and this is no longer enough:
> several machines (SPARC T5-2 among them) panic early in boot during
> USB hub enumeration with "corrupted stack end detected inside
> scheduler". sparc has not been converted to THREAD_INFO_IN_TASK, so
> thread_info sits at the bottom of the kernel stack and a marginal
> overflow corrupts it first; CONFIG_SCHED_STACK_END_CHECK then fires
> from __schedule long after the deep path has unwound, which is why
> the reported backtraces look shallow.
>
> Measurements with CONFIG_STACK_TRACER on an UltraSPARC T4-1 show the
> problem is frame count, not any single large frame. The high-water
> mark of an ordinary successful boot is 12616 of 16384 bytes (77%),
> reached in hub_probe() with a printk console flush and then a timer
> interrupt (which runs on the task stack, and whose scheduler tick
> performs load balancing and IPI delivery) stacked on top. Of the 66
> frames in that path the largest is 408 bytes, and ~85% of them are
> 176-224 bytes - at or just above the SPARC V9 ABI minimum frame
> (128-byte register window save area plus 48-byte argument save
> area). An equivalent call chain on x86-64 costs roughly a third of
> the stack, so a 16K stack on sparc64 provides far less effective
> call depth than on other 64-bit architectures.
>
> Double THREAD_SIZE to 32K (four 8K pages). The PAGE_SHIFT
> conditionals are dropped: sparc64 only supports 8K base pages, so
> the other branches were dead code. Kernel stacks become order-2
> allocations; sparc64 has no VMAP_STACK, but stacks are allocated
> once per thread and the trade against boot-time panics is a good
> one.
>
> Link: https://lore.kernel.org/all/20260519075809.8993-1-unixpro1970@gmail.com/
> Signed-off-by: Tony Rodriguez <unixpro1970@gmail.com>
> [stian: reduced the diff to the THREAD_* defines, measured stack
>   usage with CONFIG_STACK_TRACER and rewrote the changelog]
> Signed-off-by: Stian Halseth <stian@itx.no>
> ---
> v2:
>   - drop the CONFIG_SPARC64 / PAGE_SHIFT conditional chain from v1;
>     thread_info_64.h is only built on sparc64 and only 8K pages are
>     supported, so define the three constants unconditionally
>   - replace the panic backtrace in the changelog with stack tracer
>     measurements answering David Laight's review comments:
>     https://lore.kernel.org/all/20260520144104.618c75ca@pumpkin/
>   - retitled from "unify thread stack sizing and add explicit 32KB
>     stack"; the sizing logic for other configurations is unchanged
>
> Tested on an UltraSPARC T4-1, booted with the stack tracer armed
> ("stacktrace") before and after this patch. The boot high-water mark
> is 12616 bytes on both kernels - the worst path (hub_probe with a
> printk and a timer interrupt on top) is deterministic - i.e. 77% of
> the 16K stack before, 38% of the 32K stack after. DEBUG_STACK_USAGE
> agrees: the peak boot-time task shows 9208 bytes left of 16K before
> vs 25592 bytes left of 32K after (7176 bytes used in both).
>
>   arch/sparc/include/asm/thread_info_64.h | 15 +++------------
>   1 file changed, 3 insertions(+), 12 deletions(-)
>
> diff --git a/arch/sparc/include/asm/thread_info_64.h b/arch/sparc/include/asm/thread_info_64.h
> --- a/arch/sparc/include/asm/thread_info_64.h
> +++ b/arch/sparc/include/asm/thread_info_64.h
> @@ -99,13 +99,8 @@
>   #define FAULT_CODE_BLKCOMMIT	0x10	/* Use blk-commit ASI in copy_page */
>   #define	FAULT_CODE_BAD_RA	0x20	/* Bad RA for sun4v		   */
>   
> -#if PAGE_SHIFT == 13
> -#define THREAD_SIZE (2*PAGE_SIZE)
> -#define THREAD_SHIFT (PAGE_SHIFT + 1)
> -#else /* PAGE_SHIFT == 13 */
> -#define THREAD_SIZE PAGE_SIZE
> -#define THREAD_SHIFT PAGE_SHIFT
> -#endif /* PAGE_SHIFT == 13 */
> +#define THREAD_SIZE (4 * PAGE_SIZE)
> +#define THREAD_SHIFT (PAGE_SHIFT + 2)
>   
>   /*
>    * macros/functions for gaining access to the thread information structure
> @@ -128,11 +123,7 @@
>   #endif
>   
>   /* thread information allocation */
> -#if PAGE_SHIFT == 13
> -#define THREAD_SIZE_ORDER	1
> -#else /* PAGE_SHIFT == 13 */
> -#define THREAD_SIZE_ORDER	0
> -#endif /* PAGE_SHIFT == 13 */
> +#define THREAD_SIZE_ORDER	2
>   
>   #define __thread_flag_byte_ptr(ti)	\
>   	((unsigned char *)(&((ti)->flags)))
> --
> 2.53.0

Re: [PATCH v2] sparc64: increase kernel thread stack size to 32K

[Stian Halseth]

Hi Tony, 

You're welcome. 

I saw it was stuck, and wanted to push it along. Looks to me like a
proper fix that should be included.

PS: Don't want to take any credit, this is 100% your fix. If you rather
want to handle it yourself, let me know :)

-- 
Best regards
Stian Halseth



On Mon, 2026-08-31 at 11:25 -0700, Tony Rodriguez wrote:
> 
> When I compile the kernel with -fstack-usage to generate .su files,
> on 
> 7.1 kerner, the static analysis shows small stack frames for all USB 
> core functions.
> For example:
> 
> hub_event:      2457 bytes  (static)
> hub_activate:   1892 bytes  (static)
> usb_control_msg: 1248 bytes (static)
> 
> However, my runtime stack tracing shows a dramatically different
> picture:
> 
> STACKTRACE: hub_event():entry: 31856 bytes used
> STACKTRACE: hub_activate():entry: 31680 bytes used
> STACKTRACE: usb_control_msg():entry: 30768 bytes used
> 
I'm not quite sure what I'm looking at. Stack usage must _increase_
with call depth, but looks like it's decreasing?

That shouldn't be possible, but maybe I'm misreading something?

It kinda looks like you're showing sp - stack_base (space left). 

CONFIG_STACK_TRACER on the T4-1 measures 12.6K worst-case against 32K.
Could you re-measure with stacktrace on the kernel command line? 
Happy to share the exact config/procedure.
> 
> PS - I have not tested a 64K stack yet, only 32K, and this is a
> heads-up 
> recommendation.
> 
> 
> Tony
> 
> On 8/31/26 10:29 AM, Stian Halseth wrote:
> > From: Tony Rodriguez <unixpro1970@gmail.com>
> > 
> > Kernel stacks on sparc64 are 16K and this is no longer enough:
> > several machines (SPARC T5-2 among them) panic early in boot during
> > USB hub enumeration with "corrupted stack end detected inside
> > scheduler". sparc has not been converted to THREAD_INFO_IN_TASK, so
> > thread_info sits at the bottom of the kernel stack and a marginal
> > overflow corrupts it first; CONFIG_SCHED_STACK_END_CHECK then fires
> > from __schedule long after the deep path has unwound, which is why
> > the reported backtraces look shallow.
> > 
> > Measurements with CONFIG_STACK_TRACER on an UltraSPARC T4-1 show
> > the
> > problem is frame count, not any single large frame. The high-water
> > mark of an ordinary successful boot is 12616 of 16384 bytes (77%),
> > reached in hub_probe() with a printk console flush and then a timer
> > interrupt (which runs on the task stack, and whose scheduler tick
> > performs load balancing and IPI delivery) stacked on top. Of the 66
> > frames in that path the largest is 408 bytes, and ~85% of them are
> > 176-224 bytes - at or just above the SPARC V9 ABI minimum frame
> > (128-byte register window save area plus 48-byte argument save
> > area). An equivalent call chain on x86-64 costs roughly a third of
> > the stack, so a 16K stack on sparc64 provides far less effective
> > call depth than on other 64-bit architectures.
> > 
> > Double THREAD_SIZE to 32K (four 8K pages). The PAGE_SHIFT
> > conditionals are dropped: sparc64 only supports 8K base pages, so
> > the other branches were dead code. Kernel stacks become order-2
> > allocations; sparc64 has no VMAP_STACK, but stacks are allocated
> > once per thread and the trade against boot-time panics is a good
> > one.
> > 
> > Link: https://lore.kernel.org/all/20260519075809.8993-1-
> > unixpro1970@gmail.com/
> > Signed-off-by: Tony Rodriguez <unixpro1970@gmail.com>
> > [stian: reduced the diff to the THREAD_* defines, measured stack
> >   usage with CONFIG_STACK_TRACER and rewrote the changelog]
> > Signed-off-by: Stian Halseth <stian@itx.no>
> > ---
> > v2:
> >   - drop the CONFIG_SPARC64 / PAGE_SHIFT conditional chain from v1;
> >     thread_info_64.h is only built on sparc64 and only 8K pages are
> >     supported, so define the three constants unconditionally
> >   - replace the panic backtrace in the changelog with stack tracer
> >     measurements answering David Laight's review comments:
> >     https://lore.kernel.org/all/20260520144104.618c75ca@pumpkin/
> >   - retitled from "unify thread stack sizing and add explicit 32KB
> >     stack"; the sizing logic for other configurations is unchanged
> > 
> > Tested on an UltraSPARC T4-1, booted with the stack tracer armed
> > ("stacktrace") before and after this patch. The boot high-water
> > mark
> > is 12616 bytes on both kernels - the worst path (hub_probe with a
> > printk and a timer interrupt on top) is deterministic - i.e. 77% of
> > the 16K stack before, 38% of the 32K stack after. DEBUG_STACK_USAGE
> > agrees: the peak boot-time task shows 9208 bytes left of 16K before
> > vs 25592 bytes left of 32K after (7176 bytes used in both).
> > 
> >   arch/sparc/include/asm/thread_info_64.h | 15 +++------------
> >   1 file changed, 3 insertions(+), 12 deletions(-)
> > 
> > diff --git a/arch/sparc/include/asm/thread_info_64.h
> > b/arch/sparc/include/asm/thread_info_64.h
> > --- a/arch/sparc/include/asm/thread_info_64.h
> > +++ b/arch/sparc/include/asm/thread_info_64.h
> > @@ -99,13 +99,8 @@
> >   #define FAULT_CODE_BLKCOMMIT 0x10 /* Use blk-commit ASI in
> > copy_page */
> >   #define FAULT_CODE_BAD_RA 0x20 /* Bad RA for sun4v    */
> >   
> > -#if PAGE_SHIFT == 13
> > -#define THREAD_SIZE (2*PAGE_SIZE)
> > -#define THREAD_SHIFT (PAGE_SHIFT + 1)
> > -#else /* PAGE_SHIFT == 13 */
> > -#define THREAD_SIZE PAGE_SIZE
> > -#define THREAD_SHIFT PAGE_SHIFT
> > -#endif /* PAGE_SHIFT == 13 */
> > +#define THREAD_SIZE (4 * PAGE_SIZE)
> > +#define THREAD_SHIFT (PAGE_SHIFT + 2)
> >   
> >   /*
> >    * macros/functions for gaining access to the thread information
> > structure
> > @@ -128,11 +123,7 @@
> >   #endif
> >   
> >   /* thread information allocation */
> > -#if PAGE_SHIFT == 13
> > -#define THREAD_SIZE_ORDER 1
> > -#else /* PAGE_SHIFT == 13 */
> > -#define THREAD_SIZE_ORDER 0
> > -#endif /* PAGE_SHIFT == 13 */
> > +#define THREAD_SIZE_ORDER 2
> >   
> >   #define __thread_flag_byte_ptr(ti) \
> >    ((unsigned char *)(&((ti)->flags)))
> > --
> > 2.53.0

Re: [PATCH v2] sparc64: increase kernel thread stack size to 32K

[Tony Rodriguez]

Hello Stian,

**Revised for clarity.

Thanks for following up on this. As I mentioned to Andreas back in 
May/June 2026, the current combined stack usage is already very close to 
the 32K limit. If you need an immediate workaround, increasing the stack 
to 64K is probably the best option to provide enough headroom and avoid 
the stack overflow panics we are currently seeing.

While I haven't observed any panics with a 32K stack on kernel 7.1 so 
far, operating so close to the boundary is still a significant concern. 
It is worth noting that sparc64 definitely crashes with a 16K stack. 
Additionally, the Nvidia/Mellanox mlx5 driver allocates a large stack on 
sparc64, which pushes usage to the 32K boundary, and other drivers might 
do the same. Therefore, a 64K stack is far more ideal.

Regarding the kernel compilation, when I build the kernel with 
-fstack-usage to generate .su files on the 7.1 kernel, the static 
analysis shows stack frames for USB core functions. For example:

     hub_event: 2457 bytes (static)
     hub_activate: 1892 bytes (static)
     usb_control_msg: 1248 bytes (static)

However, my runtime stack tracing paints a dramatically different picture:

     STACKTRACE: hub_event():entry: 31856 bytes used
     STACKTRACE: hub_activate():entry: 31680 bytes used
     STACKTRACE: usb_control_msg():entry: 30768 bytes used

P.S. I haven't actually tested a 64K stack yet—I am offering this 
recommendation primarily based on how close the current usage is to the 
32K boundary.

Regards,
Tony

On 8/31/26 10:29 AM, Stian Halseth wrote:
> From: Tony Rodriguez<unixpro1970@gmail.com>
>
> Kernel stacks on sparc64 are 16K and this is no longer enough:
> several machines (SPARC T5-2 among them) panic early in boot during
> USB hub enumeration with "corrupted stack end detected inside
> scheduler". sparc has not been converted to THREAD_INFO_IN_TASK, so
> thread_info sits at the bottom of the kernel stack and a marginal
> overflow corrupts it first; CONFIG_SCHED_STACK_END_CHECK then fires
> from __schedule long after the deep path has unwound, which is why
> the reported backtraces look shallow.
>
> Measurements with CONFIG_STACK_TRACER on an UltraSPARC T4-1 show the
> problem is frame count, not any single large frame. The high-water
> mark of an ordinary successful boot is 12616 of 16384 bytes (77%),
> reached in hub_probe() with a printk console flush and then a timer
> interrupt (which runs on the task stack, and whose scheduler tick
> performs load balancing and IPI delivery) stacked on top. Of the 66
> frames in that path the largest is 408 bytes, and ~85% of them are
> 176-224 bytes - at or just above the SPARC V9 ABI minimum frame
> (128-byte register window save area plus 48-byte argument save
> area). An equivalent call chain on x86-64 costs roughly a third of
> the stack, so a 16K stack on sparc64 provides far less effective
> call depth than on other 64-bit architectures.
>
> Double THREAD_SIZE to 32K (four 8K pages). The PAGE_SHIFT
> conditionals are dropped: sparc64 only supports 8K base pages, so
> the other branches were dead code. Kernel stacks become order-2
> allocations; sparc64 has no VMAP_STACK, but stacks are allocated
> once per thread and the trade against boot-time panics is a good
> one.
>
> Link:https://lore.kernel.org/all/20260519075809.8993-1-unixpro1970@gmail.com/
> Signed-off-by: Tony Rodriguez<unixpro1970@gmail.com>
> [stian: reduced the diff to the THREAD_* defines, measured stack
>   usage with CONFIG_STACK_TRACER and rewrote the changelog]
> Signed-off-by: Stian Halseth<stian@itx.no>
> ---
> v2:
>   - drop the CONFIG_SPARC64 / PAGE_SHIFT conditional chain from v1;
>     thread_info_64.h is only built on sparc64 and only 8K pages are
>     supported, so define the three constants unconditionally
>   - replace the panic backtrace in the changelog with stack tracer
>     measurements answering David Laight's review comments:
>     https://lore.kernel.org/all/20260520144104.618c75ca@pumpkin/
>   - retitled from "unify thread stack sizing and add explicit 32KB
>     stack"; the sizing logic for other configurations is unchanged
>
> Tested on an UltraSPARC T4-1, booted with the stack tracer armed
> ("stacktrace") before and after this patch. The boot high-water mark
> is 12616 bytes on both kernels - the worst path (hub_probe with a
> printk and a timer interrupt on top) is deterministic - i.e. 77% of
> the 16K stack before, 38% of the 32K stack after. DEBUG_STACK_USAGE
> agrees: the peak boot-time task shows 9208 bytes left of 16K before
> vs 25592 bytes left of 32K after (7176 bytes used in both).
>
>   arch/sparc/include/asm/thread_info_64.h | 15 +++------------
>   1 file changed, 3 insertions(+), 12 deletions(-)
>
> diff --git a/arch/sparc/include/asm/thread_info_64.h b/arch/sparc/include/asm/thread_info_64.h
> --- a/arch/sparc/include/asm/thread_info_64.h
> +++ b/arch/sparc/include/asm/thread_info_64.h
> @@ -99,13 +99,8 @@
>   #define FAULT_CODE_BLKCOMMIT	0x10	/* Use blk-commit ASI in copy_page */
>   #define	FAULT_CODE_BAD_RA	0x20	/* Bad RA for sun4v		   */
>   
> -#if PAGE_SHIFT == 13
> -#define THREAD_SIZE (2*PAGE_SIZE)
> -#define THREAD_SHIFT (PAGE_SHIFT + 1)
> -#else /* PAGE_SHIFT == 13 */
> -#define THREAD_SIZE PAGE_SIZE
> -#define THREAD_SHIFT PAGE_SHIFT
> -#endif /* PAGE_SHIFT == 13 */
> +#define THREAD_SIZE (4 * PAGE_SIZE)
> +#define THREAD_SHIFT (PAGE_SHIFT + 2)
>   
>   /*
>    * macros/functions for gaining access to the thread information structure
> @@ -128,11 +123,7 @@
>   #endif
>   
>   /* thread information allocation */
> -#if PAGE_SHIFT == 13
> -#define THREAD_SIZE_ORDER	1
> -#else /* PAGE_SHIFT == 13 */
> -#define THREAD_SIZE_ORDER	0
> -#endif /* PAGE_SHIFT == 13 */
> +#define THREAD_SIZE_ORDER	2
>   
>   #define __thread_flag_byte_ptr(ti)	\
>   	((unsigned char *)(&((ti)->flags)))
> --
> 2.53.0

Re: [PATCH v2] sparc64: increase kernel thread stack size to 32K

[Tony Rodriguez]

Hi Stian,

No problem at all, and I appreciate your honesty and for reaching out. 
It’s best to get this addressed as soon as possible if you have the time 
to work on it—I’m currently swamped with other tasks. Overall, I don’t 
mind if you take over these patches, and truly appreciate your 
assistance to the sparc64 community. Just please continue to give me a 
mention in any patches related to this work, since I spent a 
considerable amount of time debugging, researching, and validating the 
fixes.

When I last tested on 7.0 and 7.1, both of my patches worked:

A)    sparc64: increase kernel thread stack size to 32K

B)    sparc64: Fix comparator problem with timer interrupts

I was able to debug and validate these issues on S7‑2 and T7‑1 hardware. 
I’m not sure if others have reported similar problems on T4 or T5 systems.

Regarding:

STACKTRACE: hub_event():entry: 31856 bytes used
STACKTRACE: hub_activate():entry: 31680 bytes used
STACKTRACE: usb_control_msg():entry: 30768 bytes used

This was a set of debugging code inserted into function hot spots and 
scripts to measure stack usage at runtime. It helped me identify trouble 
spots and gave me a better idea of where stack consumption was highest. 
At the time, I wondered whether it might be possible to reduce the stack 
size of usbcore and the Nvidia mlx5 functions on sparc64, but that would 
be a significantly more time‑consuming task. I may have updated my stack 
monitoring script since then as well.  It’s also been a few months, so 
I’d need to refresh my memory on the details.

If you have a quicker or better methodology for reviewing stack usage—or 
any general suggestions—I’m definitely open to seeing them, along with 
your config and exact procedure. And if you need help validating against 
S7‑2 and T7‑1 hardware, I can try to allocate some time to assist.

Best regards,
Tony

On 8/31/26 11:54 AM, Stian Halseth wrote:
> Hi Tony,
>
> You're welcome.
>
> I saw it was stuck, and wanted to push it along. Looks to me like a
> proper fix that should be included.
>
> PS: Don't want to take any credit, this is 100% your fix. If you rather
> want to handle it yourself, let me know :)
>

Re: [PATCH v2] sparc64: increase kernel thread stack size to 32K

[Stian Halseth]

Hi Tony,

On Mon, 2026-08-31 at 13:18 -0700, Tony Rodriguez wrote:
> Hi Stian,
> 
> Just please continue to give me a 
> mention in any patches related to this work, since I spent a 
> considerable amount of time debugging, researching, and validating
> the fixes.
Sure. For now, no real changes have been made to your patches, so as
far as I'm concerned, this is entirely your work. 
Will try help with the last mile, alongside some other patches I've
submitted.
And yes, the debugging, researching and validation is the hard part. 
Writing a fix is often _relatively_ easy, when you have all the facts.
> 
> When I last tested on 7.0 and 7.1, both of my patches worked:
> 
> A)    sparc64: increase kernel thread stack size to 32K
> 
> B)    sparc64: Fix comparator problem with timer interrupts
> 
> I was able to debug and validate these issues on S7‑2 and T7‑1
> hardware. 
Yes, and that's a very important data point. My analyzis is based on
the change itself, _and_ your validation/testing. 
> I’m not sure if others have reported similar problems on T4 or T5
> systems.
Not that I'm aware of, and I haven't seen it on my T4-1.
> 
> If you have a quicker or better methodology for reviewing stack
> usage—or 
> any general suggestions—I’m definitely open to seeing them, along
> with 
> your config and exact procedure. And if you need help validating
> against 
> S7‑2 and T7‑1 hardware, I can try to allocate some time to assist.
I think that would be very helpful. Let's try to settle the 32K-vs-64K
question with more data. 

The kernel has stack measurement built in.

The in-kernel method:
  CONFIG_STACK_TRACER=y
  CONFIG_DEBUG_STACK_USAGE=y
  CONFIG_SCHED_STACK_END_CHECK=y

Boot with "stacktrace" on the kernel command line (arms the tracer
before built-in drivers probe). Then:

  cat /sys/kernel/tracing/stack_max_size   # worst case seen, bytes
  cat /sys/kernel/tracing/stack_trace      # that path, frame by frame

Reset with "echo 0 > stack_max_size" before a workload to isolate it.

For the 32K-vs-64K question, the most valuable data you could gather
is a stack_trace snapshot on the S7-2/T7-1 under your real workload
with mlx5 active, on a 32K kernel. 

On our T4-1 the worst case is 12616 bytes, but doesn't have mlx5. If
your machines stay well under 32K, we have comfortable margin. But if
something approaches the limit, the trace will name the exact frames,
and we can judge whether the right answer is 64K or a targeted fix in
that driver.
> 

Thanks!

-- 
Best regards
Stian Halseth

Re: [PATCH v2] sparc64: increase kernel thread stack size to 32K

[Tony Rodriguez]

Thanks again for the details, but I already had those CONFIG and 
stacktrace options defined based on previous debugging sessions.

32K should be fine based on the output (see the link below), and I have 
not noticed any crashes with a 32K stack).  These results are against 
kernel v7.1.0-rc3 using my original patches on the S7-2.

https://github.com/unixpro1970/Sparc64-Kernel-Debugging-Dumps/blob/main/kernel-v7.1.0-rc3-depth-stack-trace-sparc64-s7-2.txt


Should I try your revised 32k stack and timer patches on the S7-2 and 
T7-1?  If so, which kernel version did you validate against 7.2 or 7.3?


Regards,

Tony

On 8/31/26 2:05 PM, Stian Halseth wrote:
> Hi Tony,
>
> On Mon, 2026-08-31 at 13:18 -0700, Tony Rodriguez wrote:
>> Hi Stian,
>>
>> Just please continue to give me a
>> mention in any patches related to this work, since I spent a
>> considerable amount of time debugging, researching, and validating
>> the fixes.
> Sure. For now, no real changes have been made to your patches, so as
> far as I'm concerned, this is entirely your work.
> Will try help with the last mile, alongside some other patches I've
> submitted.
> And yes, the debugging, researching and validation is the hard part.
> Writing a fix is often _relatively_ easy, when you have all the facts.
>> When I last tested on 7.0 and 7.1, both of my patches worked:
>>
>> A)    sparc64: increase kernel thread stack size to 32K
>>
>> B)    sparc64: Fix comparator problem with timer interrupts
>>
>> I was able to debug and validate these issues on S7‑2 and T7‑1
>> hardware.
> Yes, and that's a very important data point. My analyzis is based on
> the change itself, _and_ your validation/testing.
>> I’m not sure if others have reported similar problems on T4 or T5
>> systems.
> Not that I'm aware of, and I haven't seen it on my T4-1.
>> If you have a quicker or better methodology for reviewing stack
>> usage—or
>> any general suggestions—I’m definitely open to seeing them, along
>> with
>> your config and exact procedure. And if you need help validating
>> against
>> S7‑2 and T7‑1 hardware, I can try to allocate some time to assist.
> I think that would be very helpful. Let's try to settle the 32K-vs-64K
> question with more data.
>
> The kernel has stack measurement built in.
>
> The in-kernel method:
>    CONFIG_STACK_TRACER=y
>    CONFIG_DEBUG_STACK_USAGE=y
>    CONFIG_SCHED_STACK_END_CHECK=y
>
> Boot with "stacktrace" on the kernel command line (arms the tracer
> before built-in drivers probe). Then:
>
>    cat /sys/kernel/tracing/stack_max_size   # worst case seen, bytes
>    cat /sys/kernel/tracing/stack_trace      # that path, frame by frame
>
> Reset with "echo 0 > stack_max_size" before a workload to isolate it.
>
> For the 32K-vs-64K question, the most valuable data you could gather
> is a stack_trace snapshot on the S7-2/T7-1 under your real workload
> with mlx5 active, on a 32K kernel.
>
> On our T4-1 the worst case is 12616 bytes, but doesn't have mlx5. If
> your machines stay well under 32K, we have comfortable margin. But if
> something approaches the limit, the trace will name the exact frames,
> and we can judge whether the right answer is 64K or a targeted fix in
> that driver.
> Thanks!
>