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SubjectRe: [PATCH 1/2] printk: Add an option to flush all messages on panic
Hi Mukesh,

On Mon, Apr 01, 2019 at 05:20:33PM +0530, Mukesh Ojha wrote:
>
> On 4/1/2019 4:18 PM, Feng Tang wrote:
> > Current console_flush_on_panic() will only dump the new messages
> > in buffer, and users may need an opportunity to check all the
> > messages on panic which could help debugging, as user may haven't
> > seen the log before panic due to loglevel settings.
> >
> > Add a flag for console_flush_on_panic() to chose whether to
> > dump all messages.
> >
> > Signed-off-by: Feng Tang <feng.tang@intel.com>
>
>
> Looks good to me.

Thanks for the review.

>
>
> But, Will it not be good if put it under a config and not change the
> prototype, as it is a debug feature?

My understanding is the console_flush_on_panic() is also a debug
feature too :), and my 2/2 patch will has a bitmask (either controlled
by kernel cmdline or sysctl) to turn on this.

Thanks,
Feng


>
> Thanks,
> Mukesh
>
> > ---
> > arch/powerpc/kernel/traps.c | 2 +-
> > include/linux/console.h | 2 +-
> > kernel/panic.c | 2 +-
> > kernel/printk/printk.c | 9 ++++++++-
> > 4 files changed, 11 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> > index 1fd45a8..58d9580 100644
> > --- a/arch/powerpc/kernel/traps.c
> > +++ b/arch/powerpc/kernel/traps.c
> > @@ -179,7 +179,7 @@ extern void panic_flush_kmsg_end(void)
> > kmsg_dump(KMSG_DUMP_PANIC);
> > bust_spinlocks(0);
> > debug_locks_off();
> > - console_flush_on_panic();
> > + console_flush_on_panic(false);
> > }
> > static unsigned long oops_begin(struct pt_regs *regs)
> > diff --git a/include/linux/console.h b/include/linux/console.h
> > index ec9bdb3..825ecf5 100644
> > --- a/include/linux/console.h
> > +++ b/include/linux/console.h
> > @@ -175,7 +175,7 @@ extern int console_trylock(void);
> > extern void console_unlock(void);
> > extern void console_conditional_schedule(void);
> > extern void console_unblank(void);
> > -extern void console_flush_on_panic(void);
> > +extern void console_flush_on_panic(bool flush_all);
> > extern struct tty_driver *console_device(int *);
> > extern void console_stop(struct console *);
> > extern void console_start(struct console *);
> > diff --git a/kernel/panic.c b/kernel/panic.c
> > index 0ae0d73..fb77e01 100644
> > --- a/kernel/panic.c
> > +++ b/kernel/panic.c
> > @@ -277,7 +277,7 @@ void panic(const char *fmt, ...)
> > * panic() is not being callled from OOPS.
> > */
> > debug_locks_off();
> > - console_flush_on_panic();
> > + console_flush_on_panic(false);
> > panic_print_sys_info();
> > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> > index 02ca827..8ff099b 100644
> > --- a/kernel/printk/printk.c
> > +++ b/kernel/printk/printk.c
> > @@ -2525,10 +2525,11 @@ void console_unblank(void)
> > /**
> > * console_flush_on_panic - flush console content on panic
> > + * @flush_all: whether to print all messages in buffer
> > *
> > * Immediately output all pending messages no matter what.
> > */
> > -void console_flush_on_panic(void)
> > +void console_flush_on_panic(bool flush_all)
> > {
> > /*
> > * If someone else is holding the console lock, trylock will fail
> > @@ -2539,6 +2540,12 @@ void console_flush_on_panic(void)
> > */
> > console_trylock();
> > console_may_schedule = 0;
> > +
> > + /* User may want to see all the printk messages on panic */
> > + if (flush_all) {
> > + console_seq = log_first_seq;
> > + console_idx = log_first_idx;
> > + }
> > console_unlock();
> > }

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