linux-kernel - Re: [PATCH 1/1] PATCH: KGDB/KDB Fix no KDB config problem.

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Date:	Thu, 3 Oct 2013 19:15:20 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Mike Travis <travis@....com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Jason Wessel <jason.wessel@...driver.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dimitri Sivanich <sivanich@....com>,
	Hedi Berriche <hedi@....com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] PATCH: KGDB/KDB Fix no KDB config problem.


* Mike Travis <travis@....com> wrote:

> 
> 
> On 10/3/2013 9:51 AM, Ingo Molnar wrote:
> > 
> > * Mike Travis <travis@....com> wrote:
> > 
> >> Some code added to the debug_core module had KDB dependencies
> >> that it shouldn't have.
> >>
> >> Signed-off-by: Mike Travis <travis@....com>
> >> ---
> >>  kernel/debug/debug_core.c |    8 ++++----
> >>  kernel/debug/debug_core.h |    2 ++
> >>  2 files changed, 6 insertions(+), 4 deletions(-)
> >>
> >> --- linux.orig/kernel/debug/debug_core.c
> >> +++ linux/kernel/debug/debug_core.c
> >> @@ -575,8 +575,8 @@ return_normal:
> >>  		raw_spin_lock(&dbg_slave_lock);
> >>  
> >>  #ifdef CONFIG_SMP
> >> -	/* If SYSTEM_NMI, slaves are already waiting */
> >> -	if (ks->err_code == KDB_REASON_SYSTEM_NMI)
> >> +	/* If send_ready set, slaves are already waiting */
> >> +	if (ks->send_ready)
> >>  		atomic_set(ks->send_ready, 1);
> >>  
> >>  	/* Signal the other CPUs to enter kgdb_wait() */
> >> @@ -682,11 +682,11 @@ kgdb_handle_exception(int evector, int s
> >>  	if (arch_kgdb_ops.enable_nmi)
> >>  		arch_kgdb_ops.enable_nmi(0);
> >>  
> >> +	memset(ks, 0, sizeof(struct kgdb_state));
> >>  	ks->cpu			= raw_smp_processor_id();
> >>  	ks->ex_vector		= evector;
> >>  	ks->signo		= signo;
> >>  	ks->err_code		= ecode;
> >> -	ks->kgdb_usethreadid	= 0;
> >>  	ks->linux_regs		= regs;
> >>  
> >>  	if (kgdb_reenter_check(ks))
> >> @@ -750,7 +750,7 @@ int kgdb_nmicallin(int cpu, int trapnr,
> >>  		ks->cpu			= cpu;
> >>  		ks->ex_vector		= trapnr;
> >>  		ks->signo		= SIGTRAP;
> >> -		ks->err_code		= KDB_REASON_SYSTEM_NMI;
> >> +		ks->err_code		= KGDB_KDB_REASON_SYSTEM_NMI;
> >>  		ks->linux_regs		= regs;
> >>  		ks->send_ready		= send_ready;
> >>  		kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
> >> --- linux.orig/kernel/debug/debug_core.h
> >> +++ linux/kernel/debug/debug_core.h
> >> @@ -75,11 +75,13 @@ extern int kdb_stub(struct kgdb_state *k
> >>  extern int kdb_parse(const char *cmdstr);
> >>  extern int kdb_common_init_state(struct kgdb_state *ks);
> >>  extern int kdb_common_deinit_state(void);
> >> +#define KGDB_KDB_REASON_SYSTEM_NMI KDB_REASON_SYSTEM_NMI
> >>  #else /* ! CONFIG_KGDB_KDB */
> >>  static inline int kdb_stub(struct kgdb_state *ks)
> >>  {
> >>  	return DBG_PASS_EVENT;
> >>  }
> >> +#define KGDB_KDB_REASON_SYSTEM_NMI 0
> >>  #endif /* CONFIG_KGDB_KDB */
> >>  
> >>  #endif /* _DEBUG_CORE_H_ */
> > 
> > Hm, the KGDB_KDB_REASON_SYSTEM_NMI definition is a bit ugly. I still think 
> > there are layering violations here and just kludging it around doesn't 
> > solve it - a helper function that keeps kgdb details to the kgdb code 
> > would.
> > 
> > Anyway, if Jason is fine with this solution and upholds his Acked-by then 
> > I'll merge this into the first patch and apply the two patches.
> > 
> > Thanks,
> > 
> > 	Ingo
> > 
> 
> Would you prefer a simple #ifdef CONFIG_KGDB_KDB around the assignment?

An #ifdef doesn't solve the layering violation!

kernel/debug/debug_core.c didn't have any serious use of #ifdef 
CONFIG_KGDB_KDB before (it used it to flavor a few printks) and I'm not 
convinced it needs one for this feature either.

So if that whole chunk is kdb dependent, why not shuffle that into a 
nicely named function and host it somewhere appropriate in 
kernel/debug/kdb/? That function would turn into an empty inline function 
in the !CONFIG_KGDB_KDB case.

But ... it's up to Jason really whether he wants to abstract that piece of 
code out, I'm just kibitzing here really.

Thanks,

	Ingo
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