Add a missing check in nbcon driver which is causing NULL pointer dereference bug. Summary: Testing with PREEMPT_RT patch version 6.6.12 on 6.6.13 kernel and crash is seen during serial geni probe. Patch applied from:https://cdn.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patch-6.6.12-rt20.patch.gz crash signature: DMESG Log ========================= 0x0000000000000000 | 0.000000: Booting Linux on physical CPU 0x0000000000 [0x412fd050] 0x0000000000000000 | 0.000000: Linux version 6.6.13-rt20 (oe-user@oe-host) (aarch64-qcom-linux-gcc (GCC) 11.4.0, GNU ld (GNU Binutils) 2.38.20220708) #1 SMP PREEMPT_RT Tue Feb 20 17:59:33 UTC 2024 0x0000000000000000 | 0.000000: KASLR enabled 0x0000000000000000 | 0.000000: Machine model: Qualcomm Technologies, Inc. Robotics RB3gen2 addons platform 0x0000000000000000 | 0.000000: efi: EFI v2.7 by Qualcomm Technologies, Inc. 0x00000000000164F7 | 2.788805: Internal error: Oops: 0000000096000004 [#1] PREEMPT_RT SMP 0x00000000000164F7 | 2.788812: Modules linked in: 0x00000000000164F7 | 2.788818: CPU: 5 PID: 118 Comm: kworker/u16:4 Not tainted 6.6.13-rt20 #1 0x00000000000164F8 | 2.788826: Hardware name: Qualcomm Technologies, Inc. Robotics RB3gen2 addons platform (DT) 0x00000000000164F8 | 2.788830: Workqueue: events_unbound deferred_probe_work_func 0x00000000000164F8 | 2.788844: pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) 0x00000000000164F9 | 2.788852: pc : nbcon_release+0x30/0xa0 0x00000000000164F9 | 2.788865: lr : serial_core_register_port+0x4a4/0x64c 0x00000000000164F9 | 2.788877: sp : ffff8000808a39d0 0x00000000000164FA | 2.788879: x29: ffff8000808a3a00 x28: ffff8000808a3a38 x27: ffffddb447ba6718 0x00000000000164FA | 2.788890: x26: ffff6024fd9fcd30 x25: 0000000000000000 x24: ffff602400fafb60 0x00000000000164FA | 2.788899: x23: ffff602403c8c800 x22: ffff602400fafa18 x21: ffffddb448518b88 0x00000000000164FA | 2.788907: x20: ffffddb44870ac60 x19: 0000000000000000 x18: ffffddb448582b10 0x00000000000164FB | 2.788915: x17: 000000040044ffff x16: 005000f2b5503510 x15: 0000000000000000 0x00000000000164FB | 2.788924: x14: ffff6024ff5752c0 x13: 0000000000000001 x12: 0000000000000000 0x00000000000164FB | 2.788932: x11: ffff602400f7d9b0 x10: 0000000000000ba0 x9 : ffff602400f7d950 0x00000000000164FC | 2.788941: x8 : ffff8000808a3574 x7 : 0000000000000000 x6 : ffff602400cf9000 0x00000000000164FC | 2.788949: x5 : ffffddb446f93e48 x4 : ffffddb446f93e8c x3 : 0000000000000000 0x00000000000164FC | 2.788958: x2 : 0000000000000001 x1 : ffff602400cf9000 x0 : ffffddb448518b88 0x00000000000164FC | 2.788966: Call trace: 0x00000000000164FC | 2.788970: nbcon_release+0x30/0xa0 0x00000000000164FD | 2.788978: serial_core_register_port+0x4a4/0x64c 0x00000000000164FD | 2.788985: serial_ctrl_register_port+0x10/0x1c 0x00000000000164FD | 2.788993: uart_add_one_port+0x10/0x1c 0x00000000000164FD | 2.789001: qcom_geni_serial_probe+0x2a4/0x450 0x00000000000164FE | 2.789007: platform_probe+0x68/0xdc 0x00000000000164FE | 2.789016: really_probe+0x148/0x2ac 0x00000000000164FE | 2.789022: __driver_probe_device+0x78/0x12c 0x00000000000164FE | 2.789028: driver_probe_device+0x3c/0x164 0x00000000000164FF | 2.789033: __device_attach_driver+0xb8/0x140 0x00000000000164FF | 2.789039: bus_for_each_drv+0x84/0xe4 0x00000000000164FF | 2.789044: __device_attach+0xac/0x1b8 0x00000000000164FF | 2.789049: device_initial_probe+0x14/0x20 0x00000000000164FF | 2.789054: bus_probe_device+0xa8/0xac 0x00000000000164FF | 2.789059: deferred_probe_work_func+0x88/0xc0 0x0000000000016500 | 2.789064: process_one_work+0x160/0x3a8 0x0000000000016500 | 2.789072: worker_thread+0x324/0x438 0x0000000000016500 | 2.789077: kthread+0x118/0x11c 0x0000000000016500 | 2.789088: ret_from_fork+0x10/0x20 0x0000000000016501 | 2.789098: Code: f942dc23 f90017e3 d2800003 a900ffff (3942e260) 0x0000000000016501 | 2.789102: ---[ end trace 0000000000000000 ]--- 0x0000000000016501 | 2.789108: Kernel panic - not syncing: Oops: Fatal exception 0x0000000000016501 | 2.789111: SMP: stopping secondary CPUs 0x000000000001650C | 2.789446: Triggering bite 0x000000000001650C | 2.789451: platform hypervisor:qcom,gh-watchdog: Causing a QCOM Apps Watchdog bite! 0x000000000001650D | 2.789461: platform hypervisor:qcom,gh-watchdog: vWdog-CTL: 1, vWdog-time since last pet: 1349, vWdog-expired status: 1 Sahil Chandna (1): printk: fix NULL ptr dereference in nbcon driver kernel/printk/nbcon.c | 3 +++ 1 file changed, 3 insertions(+) -- 2.17.1
