Using Firefox hangs system

[Nicholas Piggin]

Excerpts from Paul Menzel's message of July 6, 2020 3:20 pm:
> Dear Nicholas,
> 
> 
> Thank you for the quick response.
> 
> 
> Am 06.07.20 um 02:41 schrieb Nicholas Piggin:
>> Excerpts from Paul Menzel's message of July 5, 2020 8:30 pm:
> 
>>> Am 05.07.20 um 11:22 schrieb Paul Menzel:
>>>> [  572.253008] Oops: Exception in kernel mode, sig: 5 [#1]
>>>> [  572.253198] LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA PowerNV
>>>> [  572.253232] Modules linked in: tcp_diag inet_diag unix_diag xt_CHECKSUM xt_MASQUERADE xt_conntrack ipt_REJECT nf_reject_ipv4 xt_tcpudp ip6table_mangle ip6table_nat iptable_mangle iptable_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nf_tables nfnetlink ip6table_filter ip6_tables iptable_filter bridge stp llc overlay xfs kvm_hv kvm binfmt_misc joydev uas usb_storage vmx_crypto bnx2x crct10dif_vpmsum ofpart cmdlinepart powernv_flash mtd mdio ibmpowernv at24 ipmi_powernv ipmi_devintf ipmi_msghandler opal_prd powernv_rng sch_fq_codel parport_pc ppdev lp nfsd parport auth_rpcgss nfs_acl lockd grace sunrpc ip_tables x_tables autofs4 btrfs blake2b_generic libcrc32c xor zstd_compress raid6_pq input_leds mac_hid hid_generic ast drm_vram_helper drm_ttm_helper i2c_algo_bit ttm drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops drm ahci drm_panel_orientation_quirks libahci usbhid hid crc32c_vpmsum uio_pdrv_genirq uio
>>>> [  572.253639] CPU: 4 PID: 6728 Comm: Web Content Not tainted 5.8.0-rc3+ #1
>>>> [  572.253659] NIP:  c00000000000ff5c LR: c00000000001a8f8 CTR: c0000000001d5f00
>>>> [  572.253835] REGS: c000007f31f0f420 TRAP: 1500   Not tainted  (5.8.0-rc3+)
>>>> [  572.253854] MSR:  900000000290b033 <SF,HV,VEC,VSX,EE,FP,ME,IR,DR,RI,LE>  CR: 28c48482  XER: 20000000
>>>> [  572.253888] CFAR: c00000000000fecc IRQMASK: 1
>>>> [  572.253888] GPR00: c00000000001b228 c000007f31f0f6b0 c000000001f9a900 c000007f351544d0
>>>> [  572.253888] GPR04: 0000000000000000 c000007f31f0fe90 c000007f351544f0 c000007f32e522b0
>>>> [  572.253888] GPR08: 0000000000000000 0000000000002000 9000000000009033 c000007fbcd85800
>>>> [  572.253888] GPR12: 0000000000008800 c000007fffffb680 0000000000000005 0000000000000004
>>>> [  572.253888] GPR16: c000007f35153800 c000007f35154130 0000000000000005 0000000000000001
>>>> [  572.253888] GPR20: 0000000000000024 c000007f32e51e68 c000007f35154028 0000007fd8da0000
>>>> [  572.253888] GPR24: 0000007fd8da0000 c000007f351544d0 c000007e9a4024d0 c000000001665f18
>>>> [  572.253888] GPR28: c000007f351544d0 c000007f35153800 900000000290f033 c000007f35153800
>>>> [  572.254079] NIP [c00000000000ff5c] save_fpu+0xa8/0x2ac
>>>> [  572.254098] LR [c00000000001a8f8] __giveup_fpu+0x28/0x80
>>>> [  572.254114] Call Trace:
>>>> [  572.254128] [c000007f31f0f6b0] [c000007f35153980] 0xc000007f35153980 (unreliable)
>>>> [  572.254156] [c000007f31f0f6e0] [c00000000001b228] giveup_all+0x128/0x150
>>>> [  572.254327] [c000007f31f0f710] [c00000000001c124] __switch_to+0x104/0x490
>>>> [  572.254352] [c000007f31f0f770] [c0000000010d2e34] __schedule+0x2e4/0xa10
>>>> [  572.254374] [c000007f31f0f840] [c0000000010d35d4] schedule+0x74/0x140
>>>> [  572.254397] [c000007f31f0f870] [c0000000010d9478] schedule_timeout+0x358/0x5d0
>>>> [  572.254424] [c000007f31f0f980] [c0000000010d5638] wait_for_completion+0xc8/0x210
>>>> [  572.254451] [c000007f31f0fa00] [c000000000608ed4] do_coredump+0x3a4/0xd60
>>>> [  572.254625] [c000007f31f0fba0] [c00000000018d1cc] get_signal+0x1dc/0xd00
>>>> [  572.254648] [c000007f31f0fcc0] [c00000000001f088] do_notify_resume+0x158/0x450
>>>> [  572.254672] [c000007f31f0fda0] [c000000000037d04] interrupt_exit_user_prepare+0x1c4/0x230
>>>> [  572.254699] [c000007f31f0fe20] [c00000000000f2b4] interrupt_return+0x14/0x1c0
>>>> [  572.254720] Instruction dump:
>>>> [  572.254882] dae60170 db060180 db260190 db4601a0 db6601b0 db8601c0 dba601d0 dbc601e0
>>>> [  572.254912] dbe601f0 48000204 38800000 f0000250 <7c062798> f0000250 38800010 f0210a50
>>>> [  572.254946] ---[ end trace ba4452ee5c77d58e ]---
>>>
>>> Please find all the messages attached.
>> 
>> "Oops: Exception in kernel mode, sig: 5 [#1]"
>> 
>> Unfortunately it's a very poor error message. I think it is a 0x1500
>> exception triggering in the kernel FP register saving. Do you have the
>> CONFIG_PPC_DENORMALISATION config option set?
> 
> Yes, as it’s set in the Ubuntu Linux kernel configuration, I have it set 
> too.
> 
>      $ grep DENORMALI /boot/config-*
>      /boot/config-4.15.0-23-generic:CONFIG_PPC_DENORMALISATION=y
>      /boot/config-5.4.0-40-generic:CONFIG_PPC_DENORMALISATION=y
>      /boot/config-5.7.0-rc5+:CONFIG_PPC_DENORMALISATION=y
>      /boot/config-5.8.0-rc3+:CONFIG_PPC_DENORMALISATION=y

Ah thanks I was able to reproduce with a little denorm test case.

The denorm interrupt handler got broken by some careless person.

This patch should hopefully fix it for you?

Thanks,
Nick

---
 arch/powerpc/kernel/exceptions-64s.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index fa080694e581..0fc8bad878b2 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -2551,7 +2551,7 @@ EXC_VIRT_NONE(0x5400, 0x100)
 INT_DEFINE_BEGIN(denorm_exception)
 	IVEC=0x1500
 	IHSRR=1
-	IBRANCH_COMMON=0
+	IBRANCH_TO_COMMON=0
 	IKVM_REAL=1
 INT_DEFINE_END(denorm_exception)
 
-- 
2.23.0