sched/group: skip group_release for kernel thread group

[wyr-7]

Summary

When CONFIG_DISABLE_PTHREAD=y, HAVE_GROUP_MEMBERS is undefined and group_leave() unconditionally calls group_release() for every exiting thread. This destroys the shared g_kthread_group resources (mutex, fdlist, task_info) while other kernel threads are still using them, causing use-after-free crashes.

PR #18517 added GROUP_FLAG_STATIC to guard group_drop() against freeing the static g_kthread_group struct. However, group_release() still runs and destroys internal resources (tg_mutex, tg_fdlist, tg_info) that are shared by all kernel threads.

Fix by checking TCB_FLAG_TTYPE_KERNEL in group_leave() before calling group_release(), so the entire release path is skipped for kernel threads. This is safe because g_kthread_group is statically allocated and its lifetime is the entire system.

Also fix the "Bits 3-7: Available" comment to "Bits 5-7" since bit 4 is now used by GROUP_FLAG_FD_BACKTRACE.

Impact

All configurations with CONFIG_DISABLE_PTHREAD=y that dynamically create and destroy kernel threads.

Testing

Tested on Infineon TC4D9 EVB (TriCore, NuttX SMP BMP). Verified kernel thread exit does not corrupt shared g_kthread_group by stopping an rptun channel (destroys rpmsg kthread).

Before rptun stop (rpmsg-corecs-0 kthread PID 48 present):

core0> ps
PID GROUP PRI POLICY TYPE NPX STATE EVENT SIGMASK STACK USED FILLED CPU COMMAND
0 0 0 FIFO Kthread - Ready 0000000000000000 0003008 0001136 37.7% 95.2% CPU0 IDLE
1 0 224 FIFO Kthread - Waiting Semaphore 0000000000000000 0003968 0001076 27.1% 0.1% hpwork 0xd0000540 0xd0000590
2 0 100 FIFO Kthread - Waiting Semaphore 0000000000000000 0003968 0001992 50.2% 0.3% lpwork 0xd00004c0 0xd0000510
3 3 253 FIFO Task - Waiting Semaphore 0000000000000000 0003904 0002820 72.2% 0.0% init
12 0 253 FIFO Kthread - Waiting Semaphore 0000000000000000 0003968 0002108 53.1% 0.0% kautocore_init
13 0 201 FIFO Kthread - Waiting Semaphore 0000000000000000 0003968 0000700 17.6% 0.7% BSW_TASK_1MS_C0
14 14 254 FIFO Task - Running 0000000000000000 0003904 0002620 67.1% 0.0% nsh
23 23 100 FIFO Task - Waiting Semaphore 0000000000000000 0003904 0002044 52.3% 0.0% dfxd -f /etc/dfxd_setup_cpu0.cfg
37 0 251 FIFO Kthread - Waiting Semaphore fffffffffff7fdff 0003968 0000564 14.2% 0.0% isrwork 0x70030f40 0x70030f90
38 0 250 FIFO Kthread - Waiting Semaphore fffffffffff7fdff 0003968 0000564 14.2% 0.0% isrwork 0x70031240 0x70031290
39 0 189 FIFO Kthread - Waiting Semaphore fffffffffff7fdff 0003904 0001372 35.1% 0.0% rpmsg-core1-0 0x70033020 0x70033070
40 0 200 FIFO Kthread - Waiting Semaphore fffffffffff7fdff 0003904 0001212 31.0% 0.0% rpmsg-core1_1-0 0x70034710 0x70034760
41 0 189 FIFO Kthread - Waiting Semaphore fffffffffff7fdff 0003904 0001372 35.1% 0.0% rpmsg-core2-0 0x70029c08 0x70029c58
42 0 189 FIFO Kthread - Waiting Semaphore fffffffffff7fdff 0003968 0001372 34.5% 0.0% rpmsg-core3-0 0x7002a2a0 0x7002a2f0
43 0 189 FIFO Kthread - Waiting Semaphore fffffffffff7fdff 0003904 0001372 35.1% 0.0% rpmsg-core4-0 0x7002a5a8 0x7002a5f8
47 0 189 FIFO Kthread - Waiting Semaphore fffffffffff7fdff 0003968 0001372 34.5% 0.0% rpmsg-core5-0 0x7002c280 0x7002c2d0
48 0 189 FIFO Kthread - Waiting Semaphore fffffffffff7fdff 0003968 0001372 34.5% 0.0% rpmsg-corecs-0 0x7002c828 0x7002c878
49 0 199 FIFO Kthread - Waiting Semaphore 0000000000000000 0003968 0001256 31.6% 0.7% BSW_TASK_5MS_C0
50 0 197 FIFO Kthread - Waiting Semaphore 0000000000000000 0003968 0001892 47.6% 2.4% BSW_TASK_10MS_C0
51 0 195 FIFO Kthread - Waiting Semaphore 0000000000000000 0003968 0001304 32.8% 0.1% BSW_TASK_20MS_C0
52 0 193 FIFO Kthread - Waiting Semaphore 0000000000000000 0003968 0001256 31.6% 0.0% BSW_TASK_50MS_C0
53 0 191 FIFO Kthread - Waiting Semaphore 0000000000000000 0003968 0001884 47.4% 0.2% BSW_TASK_100MS_C0
54 0 101 FIFO Kthread - Waiting Semaphore 0000000000000000 0003904 0001396 35.7% 0.0% autocore_macc 0xb0036094

core0> rptun stop /dev/rptun/corecs
[01/01/70 00:01:32.462760] [CPU0] rx_vq: freeing non-empty virtqueue
[01/01/70 00:01:32.462779] [CPU0] tx_vq: freeing non-empty virtqueue

After rptun stop (rpmsg-corecs-0 gone, all other kthreads intact):

core0> ps
PID GROUP PRI POLICY TYPE NPX STATE EVENT SIGMASK STACK USED FILLED CPU COMMAND
0 0 0 FIFO Kthread - Ready 0000000000000000 0003008 0001136 37.7% 95.2% CPU0 IDLE
1 0 224 FIFO Kthread - Waiting Semaphore 0000000000000000 0003968 0001076 27.1% 0.1% hpwork 0xd0000540 0xd0000590
2 0 100 FIFO Kthread - Waiting Semaphore 0000000000000000 0003968 0001992 50.2% 0.3% lpwork 0xd00004c0 0xd0000510
3 3 253 FIFO Task - Waiting Semaphore 0000000000000000 0003904 0002820 72.2% 0.0% init
12 0 253 FIFO Kthread - Waiting Semaphore 0000000000000000 0003968 0002108 53.1% 0.0% kautocore_init
13 0 201 FIFO Kthread - Waiting Semaphore 0000000000000000 0003968 0000700 17.6% 0.7% BSW_TASK_1MS_C0
14 14 254 FIFO Task - Running 0000000000000000 0003904 0003316 84.9%! 0.0% nsh
23 23 100 FIFO Task - Waiting Semaphore 0000000000000000 0003904 0002044 52.3% 0.0% dfxd -f /etc/dfxd_setup_cpu0.cfg
37 0 251 FIFO Kthread - Waiting Semaphore fffffffffff7fdff 0003968 0000564 14.2% 0.0% isrwork 0x70030f40 0x70030f90
38 0 250 FIFO Kthread - Waiting Semaphore fffffffffff7fdff 0003968 0000564 14.2% 0.0% isrwork 0x70031240 0x70031290
39 0 189 FIFO Kthread - Waiting Semaphore fffffffffff7fdff 0003904 0001372 35.1% 0.0% rpmsg-core1-0 0x70033020 0x70033070
40 0 200 FIFO Kthread - Waiting Semaphore fffffffffff7fdff 0003904 0001212 31.0% 0.0% rpmsg-core1_1-0 0x70034710 0x70034760
41 0 189 FIFO Kthread - Waiting Semaphore fffffffffff7fdff 0003904 0001372 35.1% 0.0% rpmsg-core2-0 0x70029c08 0x70029c58
42 0 189 FIFO Kthread - Waiting Semaphore fffffffffff7fdff 0003968 0001372 34.5% 0.0% rpmsg-core3-0 0x7002a2a0 0x7002a2f0
43 0 189 FIFO Kthread - Waiting Semaphore fffffffffff7fdff 0003904 0001372 35.1% 0.0% rpmsg-core4-0 0x7002a5a8 0x7002a5f8
47 0 189 FIFO Kthread - Waiting Semaphore fffffffffff7fdff 0003968 0001372 34.5% 0.0% rpmsg-core5-0 0x7002c280 0x7002c2d0
49 0 199 FIFO Kthread - Waiting Semaphore 0000000000000000 0003968 0001256 31.6% 0.7% BSW_TASK_5MS_C0
50 0 197 FIFO Kthread - Waiting Semaphore 0000000000000000 0003968 0001892 47.6% 2.3% BSW_TASK_10MS_C0
51 0 195 FIFO Kthread - Waiting Semaphore 0000000000000000 0003968 0001304 32.8% 0.1% BSW_TASK_20MS_C0
52 0 193 FIFO Kthread - Waiting Semaphore 0000000000000000 0003968 0001256 31.6% 0.0% BSW_TASK_50MS_C0
53 0 191 FIFO Kthread - Waiting Semaphore 0000000000000000 0003968 0001884 47.4% 0.1% BSW_TASK_100MS_C0
54 0 101 FIFO Kthread - Waiting Semaphore 0000000000000000 0003904 0001396 35.7% 0.0% autocore_macc 0xb0036094

System continues running normally after kthread exit. No crash, no assert, no corruption of g_kthread_group resources. PID 48 (rpmsg-corecs-0) successfully destroyed while 20+ other kernel threads sharing the same g_kthread_group remain healthy.

[acassis]

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