Re: [PATCH v2 08/13] tracing: Improve panic/die notifiers

Baoquan He
2022-08-03T09:53:49Z

On 08/03/22 at 05:36pm, Baoquan He wrote:
> On 07/19/22 at 04:53pm, Guilherme G. Piccoli wrote:
> > Currently the tracing dump_on_oops feature is implemented
> > through separate notifiers, one for die/oops and the other
> > for panic - given they have the same functionality, let's
> > unify them.
> >
> > Also improve the function comment and change the priority of
> > the notifier to make it execute earlier, avoiding showing useless
> > trace data (like the callback names for the other notifiers);
> > finally, we also removed an unnecessary header inclusion.
> >
> > Cc: Petr Mladek <pmladek@suse.com>
> > Cc: Sergei Shtylyov <sergei.shtylyov@gmail.com>
> > Cc: Steven Rostedt <rostedt@goodmis.org>
> > Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
> >
> > ---
> >
> > V2:
> > - Different approach; instead of using IDs to distinguish die and
> > panic events, rely on address comparison like other notifiers do
> > and as per Petr's suggestion;
> >
> > - Removed ACK from Steven since the code changed.
> >
> > kernel/trace/trace.c | 55 ++++++++++++++++++++++----------------------
> > 1 file changed, 27 insertions(+), 28 deletions(-)
> >
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index b8dd54627075..2a436b645c70 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -19,7 +19,6 @@
> > #include <linux/kallsyms.h>
> > #include <linux/security.h>
> > #include <linux/seq_file.h>
> > -#include <linux/notifier.h>
> > #include <linux/irqflags.h>
> > #include <linux/debugfs.h>
> > #include <linux/tracefs.h>
> > @@ -9777,40 +9776,40 @@ static __init int tracer_init_tracefs(void)
> >
> > fs_initcall(tracer_init_tracefs);
> >
> > -static int trace_panic_handler(struct notifier_block *this,
> > - unsigned long event, void *unused)
> > -{
> > - if (ftrace_dump_on_oops)
> > - ftrace_dump(ftrace_dump_on_oops);
> > - return NOTIFY_OK;
> > -}
> > +static int trace_die_panic_handler(struct notifier_block *self,
> > + unsigned long ev, void *unused);
> >
> > static struct notifier_block trace_panic_notifier = {
> > - .notifier_call = trace_panic_handler,
> > - .next = NULL,
> > - .priority = 150 /* priority: INT_MAX >= x >= 0 */
> > + .notifier_call = trace_die_panic_handler,
> > + .priority = INT_MAX - 1,
> > };
> >
> > -static int trace_die_handler(struct notifier_block *self,
> > - unsigned long val,
> > - void *data)
> > -{
> > - switch (val) {
> > - case DIE_OOPS:
> > - if (ftrace_dump_on_oops)
> > - ftrace_dump(ftrace_dump_on_oops);
> > - break;
> > - default:
> > - break;
> > - }
> > - return NOTIFY_OK;
> > -}
> > -
> > static struct notifier_block trace_die_notifier = {
> > - .notifier_call = trace_die_handler,
> > - .priority = 200
> > + .notifier_call = trace_die_panic_handler,
> > + .priority = INT_MAX - 1,
> > };
> >
> > +/*
> > + * The idea is to execute the following die/panic callback early, in order
> > + * to avoid showing irrelevant information in the trace (like other panic
> > + * notifier functions); we are the 2nd to run, after hung_task/rcu_stall
> > + * warnings get disabled (to prevent potential log flooding).
> > + */
> > +static int trace_die_panic_handler(struct notifier_block *self,
> > + unsigned long ev, void *unused)
> > +{
> > + if (!ftrace_dump_on_oops)
> > + goto out;
> > +
> > + if (self == &trace_die_notifier && ev != DIE_OOPS)
> > + goto out;
>
> Although the switch-case code of original trace_die_handler() is werid,
> this unification is not much more comfortable. Just personal feeling
> from code style, not strong opinion. Leave it to trace reviewers.

Please ignore this comment.

I use b4 to grab this patchset and applied, and started to check patch
one by one. Then I realize it's all about cleanups which have got
consensus in earlier rounds. Hope it can be merged when other people's
concern is addressed, the whole series looks good to me, I have no
strong concern to them.

>
> > +
> > + ftrace_dump(ftrace_dump_on_oops);
> > +
> > +out:
> > + return NOTIFY_DONE;
> > +}
> > +
> > /*
> > * printk is set to max of 1024, we really don't need it that big.
> > * Nothing should be printing 1000 characters anyway.
> > --
> > 2.37.1
> >
>