On Fri, 22 May 2020 at 22:05, Daniel Thompson
wrote:
>
> On Fri, May 22, 2020 at 08:03:47PM +0530, Sumit Garg wrote:
> > While rounding up CPUs via NMIs, its possible that a rounded up CPU
> > maybe holding a console port lock leading to kgdb master CPU stuck in
> > a deadlock during invocation of console write operations. So in order
> > to avoid such a deadlock, invoke bust_spinlocks() prior to invocation
> > of console handlers.
> >
> > Also, add a check for console port to be enabled prior to invocation of
> > corresponding handler.
>
> Perhaps this should have been two patches.
>
Okay, will split this patch into two.
> In fact, to be honest, I'd suggest combining all the patches to improve
> kdb console handling (including a fixed version of the RFC) into a
> single patch set.
Yeah it makes sense to have a combined patch set to improve kdb
console handling. But I posted the RFC patch separately as I expected
comments and discussions to come up with an accepted approach.
So let me wait for an agreement on RFC patch after which I can include
that patch in this patch set.
>
>
> > Suggested-by: Petr Mladek
> > Suggested-by: Sergey Senozhatsky
> > Signed-off-by: Sumit Garg
> > ---
> >
> > Changes in v2:
> > - Use oops_in_progress directly instead of bust_spinlocks().
> >
> > kernel/debug/kdb/kdb_io.c | 8
> > 1 file changed, 8 insertions(+)
> >
> > diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
> > index 924bc92..3a5a068 100644
> > --- a/kernel/debug/kdb/kdb_io.c
> > +++ b/kernel/debug/kdb/kdb_io.c
> > @@ -699,7 +699,11 @@ int vkdb_printf(enum kdb_msgsrc src, const char *fmt,
> > va_list ap)
> > }
> > }
> > for_each_console(c) {
> > + if (!(c->flags & CON_ENABLED))
> > + continue;
> > + ++oops_in_progress;
>
> Given the subtly of what is going on I think we need some comments in
> the code on what we are doing and why.
Sure, will add comments.
>
>
> > c->write(c, cp, retlen - (cp - kdb_buffer));
> > + --oops_in_progress;
> > touch_nmi_watchdog();
> > }
> > }
> > @@ -761,7 +765,11 @@ int vkdb_printf(enum kdb_msgsrc src, const char *fmt,
> > va_list ap)
> > }
> > }
> > for_each_console(c) {
> > + if (!(c->flags & CON_ENABLED))
> > + continue;
> > + ++oops_in_progress;
> > c->write(c, moreprompt, strlen(moreprompt));
> > + --oops_in_progress;
> > touch_nmi_watchdog();
>
> As with the other patches maybe the first patch in the set should be
> factoring out the common code before making changes to it.
Sure, will factor out common code as initial patch.
-Sumit
>
>
> Daniel.
