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From: "Richard W.M. Jones" <rjones@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Chuck Ebbert <cebbert.lkml@gmail.com>,
	linux-kernel@vger.kernel.org, x86@kernel.org,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [BUG 4.2-rc8] Interrupt occurs while apply_alternatives() is patching the handler
Date: Thu, 3 Sep 2015 08:53:44 +0100	[thread overview]
Message-ID: <20150903075344.GA3598@redhat.com> (raw)
In-Reply-To: <20150902190512.GG29283@redhat.com>

On Wed, Sep 02, 2015 at 08:05:12PM +0100, Richard W.M. Jones wrote:
> On Wed, Sep 02, 2015 at 11:11:55AM +0200, Thomas Gleixner wrote:
> > On Tue, 1 Sep 2015, Richard W.M. Jones wrote:
> > > On Sun, Aug 30, 2015 at 10:37:57PM -0400, Chuck Ebbert wrote:
> > > > This is from https://bugzilla.redhat.com/show_bug.cgi?id=1258223
> > > > 
> > > > [    0.036000] BUG: unable to handle kernel paging request at 55501e06
> > > [...]
> > > > [    0.036000]  [<c0409c80>] ? add_nops+0x90/0xa0
> > > > [    0.036000]  [<c040a054>] apply_alternatives+0x274/0x630
> > > > [    0.036000]  [<c07f1cf0>] ? wait_for_xmitr+0xa0/0xa0
> > > > [    0.036000]  [<c071a6fc>] ? sprintf+0x1c/0x20
> > > > [    0.036000]  [<c0aae480>] ? irq_entries_start+0x698/0x698
> > > > [    0.036000]  [<c071be4b>] ? memcpy+0xb/0x30
> > > > [    0.036000]  [<c07f3950>] ? serial8250_set_termios+0x20/0x20
> > > [...]
> > > > Interrupt 0x30 occurred while the alternatives code was replacing the
> > > > initial 0x90,0x90,0x90 NOPs (from the ASM_CLAC macro) with the optimized
> > > > version, 0x8d,0x76,0x00. Only the first byte has been replaced so far,
> > > > and it makes a mess out of the insn decoding.
> > 
> > apply_alternatives() has two ways to modify the code:
> > 
> > 1) text_poke_early()
> > 
> > 2) optimize_nops()
> > 
> > The former disables interrupts, the latter not. The patch below should
> > fix the issue.
> 
> It has gone through about 1100 iterations so far without hitting the
> bug.  I'll leave it running overnight.

That ran ~ 4000 iterations overnight, so it seems to work.  You can
add:

  Tested-by: Richard W.M. Jones <rjones@redhat.com>

Thanks,

Rich.

> Rich.
> 
> > Thanks,
> > 
> > 	tglx
> > 
> > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> > index c42827eb86cf..6a2f93e029f4 100644
> > --- a/arch/x86/kernel/alternative.c
> > +++ b/arch/x86/kernel/alternative.c
> > @@ -257,6 +257,9 @@ void __init arch_init_ideal_nops(void)
> >  /* Use this to add nops to a buffer, then text_poke the whole buffer. */
> >  static void __init_or_module add_nops(void *insns, unsigned int len)
> >  {
> > +	unsigned long flags;
> > +
> > +	local_irq_save(flags);
> >  	while (len > 0) {
> >  		unsigned int noplen = len;
> >  		if (noplen > ASM_NOP_MAX)
> > @@ -265,6 +268,7 @@ static void __init_or_module add_nops(void *insns, unsigned int len)
> >  		insns += noplen;
> >  		len -= noplen;
> >  	}
> > +	local_irq_restore(flags);
> >  }
> >  
> >  extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
> > 
> > 
> > 
> 
> -- 
> Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
> virt-builder quickly builds VMs from scratch
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-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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  reply	other threads:[~2015-09-03  7:53 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-08-31  2:37 Chuck Ebbert
2015-09-01  6:20 ` Richard W.M. Jones
2015-09-02  9:11   ` Thomas Gleixner
2015-09-02 19:05     ` Richard W.M. Jones
2015-09-03  7:53       ` Richard W.M. Jones [this message]
2015-09-03  8:50     ` Borislav Petkov
2015-09-03 10:41       ` Thomas Gleixner
2015-09-03 12:43         ` Josh Boyer
2015-09-03 13:01           ` Thomas Gleixner
2015-09-03 15:48         ` Richard W.M. Jones
2015-09-03 19:30         ` [tip:x86/urgent] x86/alternatives: Make optimize_nops() interrupt safe and synced tip-bot for Thomas Gleixner
2015-09-04  7:40         ` [BUG 4.2-rc8] Interrupt occurs while apply_alternatives() is patching the handler Richard W.M. Jones
2015-09-04 12:02         ` Borislav Petkov
2015-09-04 13:37           ` Thomas Gleixner
2015-09-05 15:25             ` Borislav Petkov

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