* [PATCH v2] kdb: Make kdb_printf robust to run in NMI context
@ 2020-05-22 14:33 Sumit Garg
2020-05-22 16:35 ` Daniel Thompson
0 siblings, 1 reply; 3+ messages in thread
From: Sumit Garg @ 2020-05-22 14:33 UTC (permalink / raw)
To: kgdb-bugreport
Cc: jason.wessel, daniel.thompson, dianders, pmladek,
sergey.senozhatsky, linux-kernel, Sumit Garg
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.
Suggested-by: Petr Mladek <pmladek@suse.com>
Suggested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
---
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;
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();
}
--
2.7.4
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v2] kdb: Make kdb_printf robust to run in NMI context
2020-05-22 14:33 [PATCH v2] kdb: Make kdb_printf robust to run in NMI context Sumit Garg
@ 2020-05-22 16:35 ` Daniel Thompson
2020-05-26 7:57 ` Sumit Garg
0 siblings, 1 reply; 3+ messages in thread
From: Daniel Thompson @ 2020-05-22 16:35 UTC (permalink / raw)
To: Sumit Garg
Cc: kgdb-bugreport, jason.wessel, dianders, pmladek,
sergey.senozhatsky, linux-kernel
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.
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.
> Suggested-by: Petr Mladek <pmladek@suse.com>
> Suggested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
> ---
>
> 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.
> 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.
Daniel.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v2] kdb: Make kdb_printf robust to run in NMI context
2020-05-22 16:35 ` Daniel Thompson
@ 2020-05-26 7:57 ` Sumit Garg
0 siblings, 0 replies; 3+ messages in thread
From: Sumit Garg @ 2020-05-26 7:57 UTC (permalink / raw)
To: Daniel Thompson
Cc: kgdb-bugreport, Jason Wessel, Douglas Anderson, Petr Mladek,
Sergey Senozhatsky, Linux Kernel Mailing List
On Fri, 22 May 2020 at 22:05, Daniel Thompson
<daniel.thompson@linaro.org> 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 <pmladek@suse.com>
> > Suggested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> > Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
> > ---
> >
> > 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.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2020-05-26 7:57 UTC | newest]
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2020-05-22 14:33 [PATCH v2] kdb: Make kdb_printf robust to run in NMI context Sumit Garg
2020-05-22 16:35 ` Daniel Thompson
2020-05-26 7:57 ` Sumit Garg
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