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From:   Qian Cai <cai@lca.pw>
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Date:   Thu, 16 Apr 2020 22:40:46 -0400
Subject: Re: POWER9 crash due to STRICT_KERNEL_RWX (WAS: Re: Linux-next POWER9 NULL pointer NIP...)
Message-Id: <43EE54C0-6F20-4ADD-9948-21F24D90C5E1@lca.pw>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Nicholas Piggin <npiggin@gmail.com>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        LKML <linux-kernel@vger.kernel.org>
To:     Russell Currey <ruscur@russell.cc>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On Apr 16, 2020, at 10:27 PM, Russell Currey <ruscur@russell.cc> wrote:
>=20
> Reverting the patch with the given config will have the same effect as
> STRICT_KERNEL_RWX=3Dn.  Not discounting that it could be a bug on the
> powerpc side (i.e. relocatable kernels with strict RWX on haven't been
> exhaustively tested yet), but we should definitely figure out what's
> going on with this bad access first.

BTW, this bad access only happened once. The overwhelming rest of crashes ar=
e with NULL pointer NIP like below. How can you explain that STRICT_KERNEL_R=
WX=3Dn would also make those NULL NIP disappear if STRICT_KERNEL_RWX is just=
 a messenger?

[  215.281666][T16896] LTP: starting chown04_16
[  215.424203][T18297] BUG: Unable to handle kernel instruction fetch (NULL p=
ointer?)
[  215.424289][T18297] Faulting instruction address: 0x00000000
[  215.424313][T18297] Oops: Kernel access of bad area, sig: 11 [#1]
[  215.424341][T18297] LE PAGE_SIZE=3D64K MMU=3DRadix SMP NR_CPUS=3D256 DEBU=
G_PAGEALLOC NUMA PowerNV
[  215.424383][T18297] Modules linked in: loop kvm_hv kvm ip_tables x_tables=
 xfs sd_mod bnx2x mdio tg3 ahci libahci libphy libata firmware_class dm_mirr=
or dm_region_hash dm_log dm_mod
[  215.424459][T18297] CPU: 85 PID: 18297 Comm: chown04_16 Tainted: G       =
 W         5.6.0-next-20200405+ #3
[  215.424489][T18297] NIP:  0000000000000000 LR: c00800000fbc0408 CTR: 0000=
000000000000
[  215.424530][T18297] REGS: c000200b8606f990 TRAP: 0400   Tainted: G       =
 W          (5.6.0-next-20200405+)
[  215.424570][T18297] MSR:  9000000040009033 <SF,HV,EE,ME,IR,DR,RI,LE>  CR:=
 84000248  XER: 20040000
[  215.424619][T18297] CFAR: c00800000fbc64f4 IRQMASK: 0=20
[  215.424619][T18297] GPR00: c0000000006c2238 c000200b8606fc20 c00000000165=
ce00 0000000000000000=20
[  215.424619][T18297] GPR04: c000201a58106400 c000200b8606fcc0 000000005f03=
7e7d ffffffff00013bfb=20
[  215.424619][T18297] GPR08: c000201a58106400 0000000000000000 000000000000=
0000 c000000001652ee0=20
[  215.424619][T18297] GPR12: 0000000000000000 c000201fff69a600 000000000000=
0000 0000000000000000=20
[  215.424619][T18297] GPR16: 0000000000000000 0000000000000000 000000000000=
0000 0000000000000000=20
[  215.424619][T18297] GPR20: 0000000000000000 0000000000000000 000000000000=
0000 0000000000000007=20
[  215.424619][T18297] GPR24: 0000000000000000 0000000000000000 c00800000fbc=
8688 c000200b8606fcc0=20
[  215.424619][T18297] GPR28: 0000000000000000 000000007fffffff c00800000fbc=
0400 c00020068b8c0e70=20
[  215.424914][T18297] NIP [0000000000000000] 0x0
[  215.424953][T18297] LR [c00800000fbc0408] find_free_cb+0x8/0x30 [loop]
find_free_cb at drivers/block/loop.c:2129
[  215.424997][T18297] Call Trace:
[  215.425036][T18297] [c000200b8606fc20] [c0000000006c2290] idr_for_each+0x=
f0/0x170 (unreliable)
[  215.425073][T18297] [c000200b8606fca0] [c00800000fbc2744] loop_lookup.par=
t.2+0x4c/0xb0 [loop]
loop_lookup at drivers/block/loop.c:2144
[  215.425105][T18297] [c000200b8606fce0] [c00800000fbc3558] loop_control_io=
ctl+0x120/0x1d0 [loop]
[  215.425149][T18297] [c000200b8606fd40] [c0000000004eb688] ksys_ioctl+0xd8=
/0x130
[  215.425190][T18297] [c000200b8606fd90] [c0000000004eb708] sys_ioctl+0x28/=
0x40
[  215.425233][T18297] [c000200b8606fdb0] [c00000000003cc30] system_call_exc=
eption+0x110/0x1e0
[  215.425274][T18297] [c000200b8606fe20] [c00000000000c9f0] system_call_com=
mon+0xf0/0x278
[  215.425314][T18297] Instruction dump:
[  215.425338][T18297] XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX=
 XXXXXXXX XXXXXXXX=20
[  215.425374][T18297] XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX=
 XXXXXXXX XXXXXXXX=20
[  215.425422][T18297] ---[ end trace ebed248fad431966 ]---
[  215.642114][T18297]=20
[  216.642220][T18297] Kernel panic - not syncing: Fatal exception=