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Date: Mon, 27 Mar 2017 11:04:41 +1100
From: Paul Mackerras <paulus@ozlabs.org>
To: Denis Kirjanov <kda@linux-powerpc.org>
Cc: linuxppc-dev <linuxppc-dev@ozlabs.org>,
 Benjamin Herrenschmidt <benh@kernel.crashing.org>,
 Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: kvmppc: BUG: using smp_processor_id() in preemptible
Message-ID: <20170327000441.GA21072@fergus.ozlabs.ibm.com>
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On Sat, Mar 25, 2017 at 03:00:27PM +0300, Denis Kirjanov wrote:
> [Now with the proper subject]
> 
> Hi,
> 
> the commit 5a319350a46572d073042a3194676099dd2c135d
> has introduces the following warning with CONFIG_DEBUG_PREEMPT enabled:
> 
> [  129.314426] BUG: using smp_processor_id() in preemptible [00000000]
> code: modprobe/5459
> [  129.314580] caller is .kvmppc_book3s_init_hv+0x184/0x350 [kvm_hv]
> [  129.314697] CPU: 11 PID: 5459 Comm: modprobe Not tainted
> 4.11.0-rc3-00022-gc7e790c #1
> [  129.314848] Call Trace:
> [  129.314915] [c0000007d624b810] [c0000000023eef10]
> .dump_stack+0xe4/0x150 (unreliable)
> [  129.315065] [c0000007d624b8a0] [c000000001f6ec04]
> .check_preemption_disabled+0x134/0x150
> [  129.315210] [c0000007d624b940] [d00000000a010274]
> .kvmppc_book3s_init_hv+0x184/0x350 [kvm_hv]
> [  129.315339] [c0000007d624ba00] [c00000000191d5cc] .do_one_initcall+0x5c/0x1c0
> [  129.315416] [c0000007d624bad0] [c0000000023e9494] .do_init_module+0x84/0x240
> [  129.315492] [c0000007d624bb70] [c000000001aade18] .load_module+0x1f68/0x2a10
> [  129.315568] [c0000007d624bd20] [c000000001aaeb30] .SyS_finit_module+0xc0/0xf0
> [  129.315645] [c0000007d624be30] [c00000000191baec] system_call+0x38/0xfc
> 
> I think that we have to explicitly add a call to preempt_disable to
> the get_paca() macro with the CONFIG_DEBUG_PREEMPT enabled.
> 
> Probably we need to create a common accessor function since we already
> have a special cases like svcpu_get/svcpu_put
> 
> If you agree I'm going send a patch.

I don't think we should put a preempt_disable() in get_paca().  If we
did that then we would also have to make a put_paca() that does
preempt_enable() and add a call to put_paca() everywhere that we call
get_paca().

All we really need to do is add a preempt_disable/enable pair in
kvmppc_book3s_init_hv().

Paul.