LoongArch: Clear FPU/SIMD thread info flags for kernel thread

If a kernel thread is created by a user thread, it may carry FPU/SIMD
thread info flags (TIF_USEDFPU, TIF_USEDSIMD, etc.). Then it will be
considered as a fpu owner and kernel try to save its FPU/SIMD context
and cause such errors:

[   41.518931] do_fpu invoked from kernel context![#1]:
[   41.523933] CPU: 1 PID: 395 Comm: iou-wrk-394 Not tainted 6.1.0-rc5+ #217
[   41.530757] Hardware name: Loongson Loongson-3A5000-7A1000-1w-CRB/Loongson-LS3A5000-7A1000-1w-CRB, BIOS vUDK2018-LoongArch-V2.0.pre-beta8 08/18/2022
[   41.544064] $ 0   : 0000000000000000 90000000011e9468 9000000106c7c000 9000000106c7fcf0
[   41.552101] $ 4   : 9000000106305d40 9000000106689800 9000000106c7fd08 0000000003995818
[   41.560138] $ 8   : 0000000000000001 90000000009a72e4 0000000000000020 fffffffffffffffc
[   41.568174] $12   : 0000000000000000 0000000000000000 0000000000000020 00000009aab7e130
[   41.576211] $16   : 00000000000001ff 0000000000000407 0000000000000001 0000000000000000
[   41.584247] $20   : 0000000000000000 0000000000000001 9000000106c7fd70 90000001002f0400
[   41.592284] $24   : 0000000000000000 900000000178f740 90000000011e9834 90000001063057c0
[   41.600320] $28   : 0000000000000000 0000000000000001 9000000006826b40 9000000106305140
[   41.608356] era   : 9000000000228848 _save_fp+0x0/0xd8
[   41.613542] ra    : 90000000011e9468 __schedule+0x568/0x8d0
[   41.619160] CSR crmd: 000000b0
[   41.619163] CSR prmd: 00000000
[   41.622359] CSR euen: 00000000
[   41.625558] CSR ecfg: 00071c1c
[   41.628756] CSR estat: 000f0000
[   41.635239] ExcCode : f (SubCode 0)
[   41.638783] PrId  : 0014c010 (Loongson-64bit)
[   41.643191] Modules linked in: acpi_ipmi vfat fat ipmi_si ipmi_devintf cfg80211 ipmi_msghandler rfkill fuse efivarfs
[   41.653734] Process iou-wrk-394 (pid: 395, threadinfo=0000000004ebe913, task=00000000636fa1be)
[   41.662375] Stack : 00000000ffff0875 9000000006800ec0 9000000006800ec0 90000000002d57e0
[   41.670412]         0000000000000001 0000000000000000 9000000106535880 0000000000000001
[   41.678450]         9000000105291800 0000000000000000 9000000105291838 900000000178e000
[   41.686487]         9000000106c7fd90 9000000106305140 0000000000000001 90000000011e9834
[   41.694523]         00000000ffff0875 90000000011f034c 9000000105291838 9000000105291830
[   41.702561]         0000000000000000 9000000006801440 00000000ffff0875 90000000002d48c0
[   41.710597]         9000000128800001 9000000106305140 9000000105291838 9000000105291838
[   41.718634]         9000000105291830 9000000107811740 9000000105291848 90000000009bf1e0
[   41.726672]         9000000105291830 9000000107811748 2d6b72772d756f69 0000000000343933
[   41.734708]         0000000000000000 0000000000000000 0000000000000000 0000000000000000
[   41.742745]         ...
[   41.745252] Call Trace:
[   42.197868] [<9000000000228848>] _save_fp+0x0/0xd8
[   42.205214] [<90000000011ed468>] __schedule+0x568/0x8d0
[   42.210485] [<90000000011ed834>] schedule+0x64/0xd4
[   42.215411] [<90000000011f434c>] schedule_timeout+0x88/0x188
[   42.221115] [<90000000009c36d0>] io_wqe_worker+0x184/0x350
[   42.226645] [<9000000000221cf0>] ret_from_kernel_thread+0xc/0x9c

This can be easily triggered by ltp testcase syscalls/io_uring02 and it
can also be easily fixed by clearing the FPU/SIMD thread info flags for
kernel threads in copy_thread().

Cc: stable@vger.kernel.org
Reported-by: Qi Hu <huqi@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/kernel/process.c

@@ -152,7 +152,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 		childregs->csr_crmd = p->thread.csr_crmd;
 		childregs->csr_prmd = p->thread.csr_prmd;
 		childregs->csr_ecfg = p->thread.csr_ecfg;
-		return 0;
+		goto out;
 	}
 
 	/* user thread */
@@ -171,14 +171,15 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 	 */
 	childregs->csr_euen = 0;
 
+	if (clone_flags & CLONE_SETTLS)
+		childregs->regs[2] = tls;
+
+out:
 	clear_tsk_thread_flag(p, TIF_USEDFPU);
 	clear_tsk_thread_flag(p, TIF_USEDSIMD);
 	clear_tsk_thread_flag(p, TIF_LSX_CTX_LIVE);
 	clear_tsk_thread_flag(p, TIF_LASX_CTX_LIVE);
 
-	if (clone_flags & CLONE_SETTLS)
-		childregs->regs[2] = tls;
-
 	return 0;
 }