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SubjectRe: [BUG 4.2-rc8] Interrupt occurs while apply_alternatives() is patching the handler
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.
>
> 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) {

I guess you want to optimize the len==0 case to not disable interrupts
needlessly:

if (!len)
return;

local_irq_save(flags);
while (len > 0)
...

Other than that, good catch!

Thanks.

--
Regards/Gruss,
Boris.

ECO tip #101: Trim your mails when you reply.
--


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