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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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.