Messages in this thread |  | | Subject | Re: Traceback due to 'powerpc/mm: Fix kernel RAM protection...' when running ppc image in qemu | From | Christophe LEROY <> | Date | Mon, 25 Sep 2017 08:36:55 +0200 |
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Le 24/09/2017 à 18:05, Guenter Roeck a écrit : > On 09/21/2017 11:44 AM, Christophe LEROY wrote: >> >> >> Le 20/09/2017 à 05:45, Guenter Roeck a écrit : >>> On 09/19/2017 08:05 PM, Michael Ellerman wrote: >>>> Guenter Roeck <linux@roeck-us.net> writes: >>>> >>>>> Hi, >>>>> >>>>> I see a the following traceback when running an SMP image based on >>>>> 85xx/mpc85xx_cds_defconfig in qemu. >>>>> >>>>> ------------[ cut here ]------------ >>>>> WARNING: CPU: 0 PID: 1 at kernel/smp.c:416 >>>>> smp_call_function_many+0xcc/0x2fc >>>>> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.14.0-rc1-00009-g0666f56 #1 >>>>> task: cf830000 task.stack: cf82e000 >>>>> NIP: c00a93c8 LR: c00a9634 CTR: 00000001 >>>>> REGS: cf82fde0 TRAP: 0700 Not tainted (4.14.0-rc1-00009-g0666f56) >>>>> MSR: 00021000 <CE,ME> CR: 24000082 XER: 00000000 >>>>> >>>>> GPR00: c00a9634 cf82fe90 cf830000 c050ad3c c0015a54 00000000 >>>>> 00000001 00000001 >>>>> GPR08: 00000001 00000000 00000000 cf82e000 24000084 00000000 >>>>> c0003150 00000000 >>>>> GPR16: 00000000 00000000 00000000 00000000 00000000 00000001 >>>>> 00000000 c0510000 >>>>> GPR24: 00000000 c0015a54 00000000 c050ad3c c051823c c050ad3c >>>>> 00000025 00000000 >>>>> NIP [c00a93c8] smp_call_function_many+0xcc/0x2fc >>>>> LR [c00a9634] smp_call_function+0x3c/0x50 >>>>> Call Trace: >>>>> [cf82fe90] [00000010] 0x10 (unreliable) >>>>> [cf82fed0] [c00a9634] smp_call_function+0x3c/0x50 >>>>> [cf82fee0] [c0015d2c] flush_tlb_kernel_range+0x20/0x38 >>>>> [cf82fef0] [c001524c] mark_initmem_nx+0x154/0x16c >>>>> [cf82ff20] [c001484c] free_initmem+0x20/0x4c >>>>> [cf82ff30] [c000316c] kernel_init+0x1c/0x108 >>>>> [cf82ff40] [c000f3a8] ret_from_kernel_thread+0x5c/0x64 >>>>> Instruction dump: >>>>> 7c0803a6 7d808120 38210040 4e800020 3d20c052 812981a0 2f890000 >>>>> 40beffac >>>>> 3d20c051 8929ac64 2f890000 40beff9c <0fe00000> 4bffff94 7fc3f378 >>>>> 7f64db78 >>>>> ---[ end trace 7da7bdcf8b15ddb3 ]--- >>>> >>>> Thanks. >>>> >>>> I guess the system still runs OK otherwise, you're just seeing the >>>> warning? >>>> >>> Yes, though I am not sure if that is because there is only one active >>> CPU (there is >>> still only one if I say "-smp 4" on the qemu command line). >>> >>>>> A complete log is available at: >>>>> http://kerneltests.org/builders/qemu-ppc-master/builds/814/steps/qemubuildcommand/logs/stdio >>>>> >>>>> >>>>> Bisect points to commit 3184cc4b6f6a1dc0 ("powerpc/mm: Fix kernel >>>>> RAM protection >>>>> after freeing unused memory on PPC32"). Bisect log is attached. A >>>>> quick look >>>>> suggests that mark_initmem_nx() is called with interrupts disabled, >>>>> which >>>>> triggers the traceback. >>>> >>>> Hmm. Yes the MSR says you have interrupts disabled (EE missing). >>>> >>>> But I don't see why. start_kernel() did local_irq_enable(), so I don't >>>> understand why we got to mark_initmem_nx() with them disabled. I'll >>>> hope >>>> that Christophe has some idea. >>>> >>> Good question. I only see this with one of 9 ppc emulations, with >>> 85xx/mpc85xx_cds_defconfig >>> +CONFIG_DEVTMPFS=y +CONFIG_SMP=y. Maybe there is a platform specific >>> init function >>> which leaves interrupts disabled. Question is which one that might be. >>> >> >> Unfortunatly no, I have no idea. My three platforms (860, 885 and >> 8321) are not SMPs so that warning would not appear, but I added a >> WARN_ON(1) just become calling mark_initmem_nx(), and I can confirm >> that MSR has EE set on all three at that time. >> > > You should still be able to compile and run a SMP kernel. > mpc85xx_cds_defconfig
SMP doesn't support the 8xx, and the 83xx has hash MMU.
> without CONFIG_SMP=y does not show the warning either.
Yes that's normal, as the smp_call_function() is not called in that case, hence my test with a WARN_ON(1) just before calling mark_initram_nx()
> > Turns out interrupts are disabled in change_page_attr(), called by > mark_initmem_nx().
Oops, you're right, I missed it.
> change_page_attr() calls flush_tlb_kernel_range() with interrupts disabled. > This only happens if CONFIG_PPC_MMU_NOHASH=y. > Given that, I would assume that this will be seen with every 32 bit ppc > build which has > CONFIG_SMP=y and CONFIG_PPC_MMU_NOHASH=y. > > Maybe the problem was really introduced with commit e611939fc8ec1 > ("powerpc/mm: Ensure > change_page_attr() doesn't invalidate pinned TLBs"). From the context it > appears that > flush_tlb_kernel_range() should not be called with interrupts disabled.
Right, it looks like that warning was introduced by this commit. However, by looking at flush_tlb_page() which was the function that was called instead before that commit, there was most likely also an issue with SMP because flush_tlb_page() called with a NULL vma results in a warning in the SMP NOHASH version of flush_tlb_page().
> Indeed, moving flush_tlb_kernel_range() outside the irq disabled code fixes > the problem for me.
Yes that's likely the solution it seems.
Thanks Christophe
> > Thanks, > Guenter > >> So as you suggest, there must be a platform specific stuff leaving the >> interrupts disabled. >> >> Christophe >> >> >>> Guenter >>
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