Re: [v6][PATCH 5/5] powerpc/book3e/kgdb: Fix a single stgep case oflazy IRQ
From: Scott Wood
Date: Tue Dec 17 2013 - 21:45:48 EST
On Wed, 2013-10-23 at 17:31 +0800, Tiejun Chen wrote:
> In lazy EE magic, we may have a lazy interrupt occured while
> entering kgdb, but we really don't want to replay that interrupt
> for kgdb, so we have to clear the PACA_IRQ_HARD_DIS force to
> make sure we can exit directly from this debug exception.
>
> Signed-off-by: Tiejun Chen <tiejun.chen@xxxxxxxxxxxxx>
s/stgep/step/ in subject
> ---
> arch/powerpc/kernel/kgdb.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
> index 447c14b..9872f58 100644
> --- a/arch/powerpc/kernel/kgdb.c
> +++ b/arch/powerpc/kernel/kgdb.c
> @@ -185,6 +185,14 @@ static int kgdb_singlestep(struct pt_regs *regs)
> /* Restore current_thread_info lastly. */
> memcpy(exception_thread_info, backup_current_thread_info, sizeof *thread_info);
>
> +#ifdef CONFIG_PPC64
> + /*
> + * Clear the PACA_IRQ_HARD_DIS from the pending mask
> + * since we are about to exit this directly from debug
> + * exception without any replay interrupt in lazy EE case.
> + */
> + local_paca->irq_happened &= ~PACA_IRQ_HARD_DIS;
> +#endif
> return 1;
> }
>
What happens to those interrupts you discarded once we get back to a
state when they can be safely replayed? I don't think just dropping
them is the answer.
I'm not sure what the actual problem is. I can understand not wanting
kgdb to cause interrupts to appear to run when the interrupted context
has external interrupts disabled, but the replay code in entry_64.S
doesn't run if interrupts are soft-disabled in the context to be
returned to. What harm does it cause to run the interrupts if we're
returning to an EE=1 context?
Does KGDB enable interrupts in its handler? If not, how do we even get
into the situation where there are interrupts pending when the
interrupted context has EE soft-enabled (i.e. we went directly from a
context where the interrupt handler should have run, to a hard-disabled
context)?
-Scott
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