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

    > +
    > + 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
    >

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