We received a report from debian infra team, says their build machine crashes regularly with:
[ 4066.698500] do_cpu invoked from kernel context![#1]: [ 4066.703455] CPU: 1 PID: 76608 Comm: iou-sqp-76326 Not tainted 5.10.0-21-loongson-3 #1 Debian 5.10.162-1 [ 4066.712793] Hardware name: Loongson Lemote-3A4000-7A-1w-V1.00-A1901/Lemote-3A4000-7A-1w-V1.00-A1901, BIOS Loongson-PMON-V3.3-20201222 12/22/2020 [ 4066.725672] $ 0 : 0000000000000000 ffffffff80bf2e48 0000000000000001 9800000200804000 [ 4066.733642] $ 4 : 9800000105115280 ffffffff80db4728 0000000000000008 0000020080000200 [ 4066.741607] $ 8 : 0000000000000001 0000000000000001 0000000000000000 0000000002e85400 [ 4066.749571] $12 : 000000005400cce0 ffffffff80199c00 000000000000036f 000000000000036f [ 4066.757536] $16 : 980000010025c080 ffffffff80ec4740 0000000000000000 980000000234b8c0 [ 4066.765501] $20 : ffffffff80ec5ce0 9800000105115280 98000001051158a0 0000000000000000 [ 4066.773466] $24 : 0000000000000028 9800000200807e58 [ 4066.781431] $28 : 9800000200804000 9800000200807d40 980000000234b8c0 ffffffff80bf3074 [ 4066.789395] Hi : 00000000000002fb [ 4066.792943] Lo : 00000000428f6816 [ 4066.796500] epc : ffffffff802177c0 _save_fp+0x10/0xa0 [ 4066.801695] ra : ffffffff80bf3074 __schedule+0x804/0xe08 [ 4066.807230] Status: 5400cce2 KX SX UX KERNEL EXL [ 4066.811917] Cause : 1000002c (ExcCode 0b) [ 4066.815899] PrId : 0014c004 (ICT Loongson-3) [ 4066.820228] Modules linked in: asix usbnet mii sg ip6t_REJECT nf_reject_ipv6 ip6table_filter ip6_tables nfnetlink_log nfnetlink xt_hashlimit ipt_REJECT nf_reject_ipv4 xt_NFLOG xt_multiport xt_tcpudp xt_state xt_conntrack nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 libcrc32c iptable_filter sch_fq tcp_bbr fuse drm drm_panel_orientation_quirks configfs ip_tables x_tables autofs4 ext4 crc16 mbcache jbd2 crc32c_generic ohci_pci dm_mod r8169 realtek mdio_devres ohci_hcd ehci_pci of_mdio xhci_pci fixed_phy xhci_hcd ehci_hcd libphy usbcore usb_common [ 4066.868085] Process iou-sqp-76326 (pid: 76608, threadinfo=0000000056dd346c, task=000000001209ac62, tls=000000fff18298e0) [ 4066.878897] Stack : ffffffff80ec0000 0000000000000000 ffffffff80ec0000 980000010db34100 [ 4066.886867] 9800000100000004 d253a55201683fdc 9800000105115280 0000000000000000 [ 4066.894832] 0000000000000000 0000000000000001 980000010db340e8 0000000000000001 [ 4066.902796] 0000000000000004 0000000000000000 980000010db33d28 ffffffff80bf36d0 [ 4066.910761] 980000010db340e8 980000010db34100 980000010db340c8 ffffffff8070d740 [ 4066.918726] 980000010946cc80 9800000104b56c80 980000010db340c0 0000000000000000 [ 4066.926690] ffffffff80ec0000 980000010db340c8 980000010025c080 ffffffff80ec5ce0 [ 4066.934654] 0000000000000000 9800000105115280 ffffffff802c59b8 980000010db34108 [ 4066.942619] 980000010db34108 2d7071732d756f69 ffff003632333637 d253a55201683fdc [ 4066.950585] ffffffff8070d1c8 980000010db340c0 98000001092276c8 000000007400cce0 [ 4066.958552] ... [ 4066.960981] Call Trace: [ 4066.963414] [<ffffffff802177c0>] _save_fp+0x10/0xa0 [ 4066.968270] [<ffffffff80bf3074>] __schedule+0x804/0xe08 [ 4066.973462] [<ffffffff80bf36d0>] schedule+0x58/0x150 [ 4066.978397] [<ffffffff8070d740>] io_sq_thread+0x578/0x5a0 [ 4066.983764] [<ffffffff8020518c>] ret_from_kernel_thread+0x14/0x1c [ 4066.989823] [ 4066.991297] Code: 000c6940 05a10011 00000000 <f4810af0> f4830b10 f4850b30 f4870b50 f4890b70 f48b0b90
It seems like kernel is trying to save a FP context for a kthread. Since we don't use FPU in kernel for now, TIF_USEDFPU must be set accidentally for that kthread.
Inspecting the code it seems like create_io_thread may be invoked from threads that have FP context alive, causing TIF_USEDFPU to be copied from that context to kthread unexpectedly.
Move around code blocks to ensure flags regarding lazy hardware context get cleared for kernel threads as well.
Cc: stable@vger.kernel.org Reported-by: Aurelien Jarno aurel32@debian.org Signed-off-by: Jiaxun Yang jiaxun.yang@flygoat.com --- Folks, it might be helpful to check ST0_CU1 in is_fpu_owner to catch this kind of problem in future, what's your opinion? --- arch/mips/kernel/process.c | 35 +++++++++++++++++------------------ 1 file changed, 17 insertions(+), 18 deletions(-)
diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c index 5387ed0a5186..fecffa32f3e0 100644 --- a/arch/mips/kernel/process.c +++ b/arch/mips/kernel/process.c @@ -136,24 +136,26 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) status |= ST0_EXL; #endif childregs->cp0_status = status; - return 0; - } + } else { + /* user thread */ + *childregs = *regs; + childregs->regs[7] = 0; /* Clear error flag */ + childregs->regs[2] = 0; /* Child gets zero as return value */ + if (usp) + childregs->regs[29] = usp;
- /* user thread */ - *childregs = *regs; - childregs->regs[7] = 0; /* Clear error flag */ - childregs->regs[2] = 0; /* Child gets zero as return value */ - if (usp) - childregs->regs[29] = usp; + p->thread.reg29 = (unsigned long) childregs; + p->thread.reg31 = (unsigned long) ret_from_fork;
- p->thread.reg29 = (unsigned long) childregs; - p->thread.reg31 = (unsigned long) ret_from_fork; + /* + * New tasks lose permission to use the fpu. This accelerates context + * switching for most programs since they don't use the fpu. + */ + childregs->cp0_status &= ~(ST0_CU2|ST0_CU1);
- /* - * New tasks lose permission to use the fpu. This accelerates context - * switching for most programs since they don't use the fpu. - */ - childregs->cp0_status &= ~(ST0_CU2|ST0_CU1); + if (clone_flags & CLONE_SETTLS) + ti->tp_value = tls; + }
clear_tsk_thread_flag(p, TIF_USEDFPU); clear_tsk_thread_flag(p, TIF_USEDMSA); @@ -167,9 +169,6 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) atomic_set(&p->thread.bd_emu_frame, BD_EMUFRAME_NONE); #endif
- if (clone_flags & CLONE_SETTLS) - ti->tp_value = tls; - return 0; }