linux-kernel - Re: [PATCH v1 3/4] powerpc/code-patching: Use jump

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Date:   Wed, 18 May 2022 19:17:06 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v1 3/4] powerpc/code-patching: Use jump_label for testing
 freed initmem

On Tue, Mar 22, 2022 at 04:40:20PM +0100, Christophe Leroy wrote:
> Once init is done, initmem is freed forever so no need to
> test system_state at every call to patch_instruction().
> 
> Use jump_label.
> 
> This reduces by 2% the time needed to activate ftrace on an 8xx.
> 

It also causes the qemu mpc8544ds emulation to crash.

BUG: Unable to handle kernel data access on write at 0xc122eb34
Faulting instruction address: 0xc001b580
Oops: Kernel access of bad area, sig: 11 [#1]
BE PAGE_SIZE=4K MPC8544 DS
Modules linked in:
CPU: 0 PID: 1 Comm: swapper Not tainted 5.18.0-rc7-next-20220518 #1
NIP:  c001b580 LR: c001b560 CTR: 00000003
REGS: c5107dd0 TRAP: 0300   Not tainted  (5.18.0-rc7-next-20220518)
MSR:  00009000 <EE,ME>  CR: 24000882  XER: 00000000
DEAR: c122eb34 ESR: 00800000
GPR00: c001b560 c5107ec0 c5120020 10000000 00000000 00000078 0c000000 cfffffff
GPR08: c001e9ec 00000001 00000007 00000000 44000882 00000000 c0005178 00000000
GPR16: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
GPR24: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 c1230000
NIP [c001b580] free_initmem+0x48/0xa8
LR [c001b560] free_initmem+0x28/0xa8
Call Trace:
[c5107ec0] [c001b560] free_initmem+0x28/0xa8 (unreliable)
[c5107ee0] [c00051b0] kernel_init+0x38/0x150
[c5107f00] [c001626c] ret_from_kernel_thread+0x5c/0x64
Instruction dump:
3fe0c123 912a00dc 90010024 48000665 3d20c218 8929fa65 2c090000 41820058
813feb34 2c090000 4082003c 39200001 <913feb34> 80010024 3cc0c114 83e1001c

Reverting this patch fixes the problem.

Guenter

---
# bad: [736ee37e2e8eed7fe48d0a37ee5a709514d478b3] Add linux-next specific files for 20220518
# good: [42226c989789d8da4af1de0c31070c96726d990c] Linux 5.18-rc7
git bisect start 'HEAD' 'v5.18-rc7'
# bad: [555b5fa93f08980ccb6bc8e196226046fe047901] Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/cryptodev-2.6.git
git bisect bad 555b5fa93f08980ccb6bc8e196226046fe047901
# bad: [8f5ef5e622d3f217d6542779723566099f370c31] Merge branch 'for-next' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux.git
git bisect bad 8f5ef5e622d3f217d6542779723566099f370c31
# good: [2b7d17d4b7c1ff40f58b0d32be40fc0bb6c582fb] soc: document merges
git bisect good 2b7d17d4b7c1ff40f58b0d32be40fc0bb6c582fb
# good: [4964f9250fbf76cb0b9c1124d5b9ab65de9bfd0e] Merge branch 'clk-next' of git://git.kernel.org/pub/scm/linux/kernel/git/clk/linux.git
git bisect good 4964f9250fbf76cb0b9c1124d5b9ab65de9bfd0e
# bad: [18fae10a22071ccd0a2c44df2749ff482132774e] Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux.git
git bisect bad 18fae10a22071ccd0a2c44df2749ff482132774e
# bad: [b4a5aaaa51e4ab7f03eec509d3710d50e52e87a6] Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git
git bisect bad b4a5aaaa51e4ab7f03eec509d3710d50e52e87a6
# bad: [b6b1c3ce06ca438eb24e0f45bf0e63ecad0369f5] powerpc/rtas: Keep MSR[RI] set when calling RTAS
git bisect bad b6b1c3ce06ca438eb24e0f45bf0e63ecad0369f5
# good: [87ccc6684d3b57e3073f77cf28396b3037154193] powerpc/book3e: Fix sparse report in mm/nohash/fsl_book3e.c
git bisect good 87ccc6684d3b57e3073f77cf28396b3037154193
# good: [f31c618373f2051a32e30002d8eacad7bbbd3885] powerpc: Sort and de-dup primary opcodes in ppc-opcode.h
git bisect good f31c618373f2051a32e30002d8eacad7bbbd3885
# good: [9290c379d19774d8de6e2b895d756004dbad9ce5] powerpc/8xx: Simplify flush_tlb_kernel_range()
git bisect good 9290c379d19774d8de6e2b895d756004dbad9ce5
# bad: [d8d2af70b98109418bb16ff6638d7c1c4336f7fe] cxl/ocxl: Prepare cleanup of powerpc's asm/prom.h
git bisect bad d8d2af70b98109418bb16ff6638d7c1c4336f7fe
# bad: [b033767848c4115e486b1a51946de3bee2ac0fa6] powerpc/code-patching: Use jump_label for testing freed initmem
git bisect bad b033767848c4115e486b1a51946de3bee2ac0fa6
# good: [cb3ac45214c03852430979a43180371a44b74596] powerpc/code-patching: Don't call is_vmalloc_or_module_addr() without CONFIG_MODULES
git bisect good cb3ac45214c03852430979a43180371a44b74596
# first bad commit: [b033767848c4115e486b1a51946de3bee2ac0fa6] powerpc/code-patching: Use jump_label for testing freed initmem