extmod/zephyr_kernel: Use same priority for spawned threads as creating thread.

Root cause investigation revealed that spawned threads had higher priority
(0) than main thread (1), causing z_reschedule() to immediately preempt
during GIL bounce windows (MP_THREAD_GIL_EXIT → MP_THREAD_GIL_ENTER).

When main thread executes multi-step operations like bytearray.append()
and bounces the GIL, higher priority waiting threads would immediately
preempt, acquire the GIL, and corrupt shared data structures.

Fix matches ports/zephyr proven approach: use k_thread_priority_get() to
inherit priority from creating thread, ensuring equal priority prevents
immediate preemption during GIL bounce.

Signed-off-by: Andrew Leech <andrew@alelec.net>

Author: pi-anl

extmod/zephyr_kernel/kernel/mpthread_zephyr.c

@@ -44,7 +44,7 @@ void z_ready_thread(struct k_thread *thread);
 
 #define MP_THREAD_MIN_STACK_SIZE                (4 * 1024)
 #define MP_THREAD_DEFAULT_STACK_SIZE            (MP_THREAD_MIN_STACK_SIZE + 1024)
-#define MP_THREAD_PRIORITY                      K_PRIO_PREEMPT(0)  // Higher priority than main (1)
+#define MP_THREAD_PRIORITY                      (k_thread_priority_get(k_current_get()))  // Same priority as creating thread (matches ports/zephyr)
 #define MP_THREAD_MAXIMUM_USER_THREADS          (5)  // Reduced from 8 to save RAM (allows mutate_bytearray.py with 4 threads)
 
 // FPU context size validation

gdb_hardfault_capture.txt

@@ -0,0 +1,14 @@
+Breakpoint 1 at 0x80706f8: file stm32_it.c, line 150.
+Note: automatically using hardware breakpoints for read-only addresses.
+
+Program received signal SIGSEGV, Segmentation fault.
+0x080718c4 in usbd_msc_IsReady (warning: Could not fetch required FPCCR content.  Further unwinding is impossible.
+lun=148 '\224') at usbd_msc_interface.c:250
+250	        return -1;
+(gdb) A debugging session is active.
+
+	Inferior 1 [Remote target] will be detached.
+
+Quit anyway? (y or n) [answered Y; input not from terminal]
+Detaching from program: /home/corona/micropython/ports/stm32/build-NUCLEO_F429ZI/firmware.elf, Remote target
+[Inferior 1 (Remote target) detached]

gdb_stack_interactive.txt

@@ -0,0 +1,13 @@
+Breakpoint 1 at 0x8070844: file stm32_it.c, line 227.
+Note: automatically using hardware breakpoints for read-only addresses.
+
+Program received signal SIGSEGV, Segmentation fault.
+0x08071908 in usbd_msc_Write (lun=<optimized out>, buf=0x2000c594 <usb_device+4108> "", blk_addr=0, blk_len=<optimized out>) at usbd_msc_interface.c:310
+310	        return -1;
+(gdb) A debugging session is active.
+
+	Inferior 1 [Remote target] will be detached.
+
+Quit anyway? (y or n) [answered Y; input not from terminal]
+Detaching from program: /home/corona/micropython/ports/stm32/build-NUCLEO_F429ZI/firmware.elf, Remote target
+[Inferior 1 (Remote target) detached]

gdb_stack_interactive_output.txt

@@ -0,0 +1,36 @@
+GNU gdb (Arm GNU Toolchain 14.3.Rel1 (Build arm-14.174)) 15.2.90.20241229-git
+Copyright (C) 2024 Free Software Foundation, Inc.
+License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
+This is free software: you are free to change and redistribute it.
+There is NO WARRANTY, to the extent permitted by law.
+Type "show copying" and "show warranty" for details.
+This GDB was configured as "--host=x86_64-pc-linux-gnu --target=arm-none-eabi".
+Type "show configuration" for configuration details.
+For bug reporting instructions, please see:
+<https://bugs.linaro.org/>.
+Find the GDB manual and other documentation resources online at:
+    <http://www.gnu.org/software/gdb/documentation/>.
+
+For help, type "help".
+Type "apropos word" to search for commands related to "word"...
+Reading symbols from ports/stm32/build-NUCLEO_F429ZI/firmware.elf...
+0x08071908 in usbd_msc_Write (lun=<optimized out>, 
+    buf=0x2000c594 <usb_device+4108> "", blk_addr=0, blk_len=<optimized out>)
+    at usbd_msc_interface.c:310
+310	        return -1;
+Warning: 'set logging on', an alias for the command 'set logging enabled', is deprecated.
+Use 'set logging enabled on'.
+
+Breakpoint 1 at 0x8070844: file stm32_it.c, line 227.
+Note: automatically using hardware breakpoints for read-only addresses.
+
+Program received signal SIGSEGV, Segmentation fault.
+0x08071908 in usbd_msc_Write (lun=<optimized out>, buf=0x2000c594 <usb_device+4108> "", blk_addr=0, blk_len=<optimized out>) at usbd_msc_interface.c:310
+310	        return -1;
+(gdb) A debugging session is active.
+
+	Inferior 1 [Remote target] will be detached.
+
+Quit anyway? (y or n) [answered Y; input not from terminal]
+Detaching from program: /home/corona/micropython/ports/stm32/build-NUCLEO_F429ZI/firmware.elf, Remote target
+[Inferior 1 (Remote target) detached]

gdb_stack_sentinel_check.txt

@@ -0,0 +1,13 @@
+Breakpoint 1 at 0x8070844: file stm32_it.c, line 227.
+Note: automatically using hardware breakpoints for read-only addresses.
+
+Program received signal SIGSEGV, Segmentation fault.
+0x08071908 in usbd_msc_Write (lun=<optimized out>, buf=0x2000c594 <usb_device+4108> "", blk_addr=0, blk_len=<optimized out>) at usbd_msc_interface.c:310
+310	        return -1;
+(gdb) A debugging session is active.
+
+	Inferior 1 [Remote target] will be detached.
+
+Quit anyway? (y or n) [answered Y; input not from terminal]
+Detaching from program: /home/corona/micropython/ports/stm32/build-NUCLEO_F429ZI/firmware.elf, Remote target
+[Inferior 1 (Remote target) detached]

gdb_thread_fault.txt

@@ -0,0 +1,11 @@
+Function "mp_thread_create_ex" not defined.
+Make breakpoint pending on future shared library load? (y or [n]) [answered N; input not from terminal]
+/home/corona/mpy/thread/capture_thread_fault.gdb:19: Error in sourced command file:
+Argument required (one or more breakpoint numbers).
+(gdb) A debugging session is active.
+
+	Inferior 1 [Remote target] will be detached.
+
+Quit anyway? (y or n) [answered Y; input not from terminal]
+Detaching from program: /home/corona/micropython/ports/stm32/build-NUCLEO_F429ZI/firmware.elf, Remote target
+[Inferior 1 (Remote target) detached]