diff mbox series

[23/30] printk: kmsg_dump: Introduce helper to inform number of dumpers

Message ID 20220427224924.592546-24-gpiccoli@igalia.com (mailing list archive)
State Not Applicable
Headers show
Series The panic notifiers refactor | expand

Commit Message

Guilherme G. Piccoli April 27, 2022, 10:49 p.m. UTC
Currently we don't have a way to check if there are dumpers set,
except counting the list members maybe. This patch introduces a very
simple helper to provide this information, by just keeping track of
registered/unregistered kmsg dumpers. It's going to be used on the
panic path in the subsequent patch.

Notice that the spinlock guarding kmsg_dumpers list also guards
increment/decrement of the dumper's counter, but there's no need
for that when reading the counter in the panic path, since that is
an atomic path and there's no other (planned) user.

Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
---
 include/linux/kmsg_dump.h |  7 +++++++
 kernel/printk/printk.c    | 14 ++++++++++++++
 2 files changed, 21 insertions(+)

Comments

Steven Rostedt May 10, 2022, 5:40 p.m. UTC | #1
On Wed, 27 Apr 2022 19:49:17 -0300
"Guilherme G. Piccoli" <gpiccoli@igalia.com> wrote:

> Currently we don't have a way to check if there are dumpers set,
> except counting the list members maybe. This patch introduces a very
> simple helper to provide this information, by just keeping track of
> registered/unregistered kmsg dumpers. It's going to be used on the
> panic path in the subsequent patch.

FYI, it is considered "bad form" to reference in the change log "this
patch". We know this is a patch. The change log should just talk about what
is being done. So can you reword your change logs (you do this is almost
every patch). Here's what I would reword the above to be:

 Currently we don't have a way to check if there are dumpers set, except
 perhaps by counting the list members. Introduce a very simple helper to
 provide this information, by just keeping track of registered/unregistered
 kmsg dumpers. This will simplify the refactoring of the panic path.


-- Steve
Guilherme G. Piccoli May 11, 2022, 8:03 p.m. UTC | #2
On 10/05/2022 14:40, Steven Rostedt wrote:
> On Wed, 27 Apr 2022 19:49:17 -0300
> "Guilherme G. Piccoli" <gpiccoli@igalia.com> wrote:
> 
>> Currently we don't have a way to check if there are dumpers set,
>> except counting the list members maybe. This patch introduces a very
>> simple helper to provide this information, by just keeping track of
>> registered/unregistered kmsg dumpers. It's going to be used on the
>> panic path in the subsequent patch.
> 
> FYI, it is considered "bad form" to reference in the change log "this
> patch". We know this is a patch. The change log should just talk about what
> is being done. So can you reword your change logs (you do this is almost
> every patch). Here's what I would reword the above to be:
> 
>  Currently we don't have a way to check if there are dumpers set, except
>  perhaps by counting the list members. Introduce a very simple helper to
>  provide this information, by just keeping track of registered/unregistered
>  kmsg dumpers. This will simplify the refactoring of the panic path.

Thanks for the hint, you're right - it's almost in all of my patches.
I'll reword all of them (except the ones already merged) to remove this
"bad form".

Cheers,


Guilherme
Petr Mladek May 16, 2022, 2:50 p.m. UTC | #3
On Wed 2022-05-11 17:03:51, Guilherme G. Piccoli wrote:
> On 10/05/2022 14:40, Steven Rostedt wrote:
> > On Wed, 27 Apr 2022 19:49:17 -0300
> > "Guilherme G. Piccoli" <gpiccoli@igalia.com> wrote:
> > 
> >> Currently we don't have a way to check if there are dumpers set,
> >> except counting the list members maybe. This patch introduces a very
> >> simple helper to provide this information, by just keeping track of
> >> registered/unregistered kmsg dumpers. It's going to be used on the
> >> panic path in the subsequent patch.
> > 
> > FYI, it is considered "bad form" to reference in the change log "this
> > patch". We know this is a patch. The change log should just talk about what
> > is being done. So can you reword your change logs (you do this is almost
> > every patch). Here's what I would reword the above to be:
> > 
> >  Currently we don't have a way to check if there are dumpers set, except
> >  perhaps by counting the list members. Introduce a very simple helper to
> >  provide this information, by just keeping track of registered/unregistered
> >  kmsg dumpers. This will simplify the refactoring of the panic path.
> 
> Thanks for the hint, you're right - it's almost in all of my patches.
> I'll reword all of them (except the ones already merged) to remove this
> "bad form".

Shame on me that I do not care that much about the style of the commit
message :-)

Anyway, the code looks good to me. With the better commit message:

Reviewed-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr
Guilherme G. Piccoli May 16, 2022, 4:09 p.m. UTC | #4
On 16/05/2022 11:50, Petr Mladek wrote:
> [...]
> Shame on me that I do not care that much about the style of the commit
> message :-)
> 
> Anyway, the code looks good to me. With the better commit message:
> 
> Reviewed-by: Petr Mladek <pmladek@suse.com>
> 

Heheh, cool - I'll add your tag and improve the message in V2.
Thanks,


Guilherme
diff mbox series

Patch

diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 906521c2329c..abea1974bff8 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -65,6 +65,8 @@  bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 
 void kmsg_dump_rewind(struct kmsg_dump_iter *iter);
 
+bool kmsg_has_dumpers(void);
+
 int kmsg_dump_register(struct kmsg_dumper *dumper);
 
 int kmsg_dump_unregister(struct kmsg_dumper *dumper);
@@ -91,6 +93,11 @@  static inline void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
 }
 
+static inline bool kmsg_has_dumpers(void)
+{
+	return false;
+}
+
 static inline int kmsg_dump_register(struct kmsg_dumper *dumper)
 {
 	return -EINVAL;
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index da03c15ecc89..e3a1c429fbbc 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3399,6 +3399,18 @@  EXPORT_SYMBOL(printk_timed_ratelimit);
 
 static DEFINE_SPINLOCK(dump_list_lock);
 static LIST_HEAD(dump_list);
+static int num_dumpers;
+
+/**
+ * kmsg_has_dumpers - inform if there is any kmsg dumper registered.
+ *
+ * Returns true if there's at least one registered dumper, or false
+ * if otherwise.
+ */
+bool kmsg_has_dumpers(void)
+{
+	return num_dumpers ? true : false;
+}
 
 /**
  * kmsg_dump_register - register a kernel log dumper.
@@ -3423,6 +3435,7 @@  int kmsg_dump_register(struct kmsg_dumper *dumper)
 		dumper->registered = 1;
 		list_add_tail_rcu(&dumper->list, &dump_list);
 		err = 0;
+		num_dumpers++;
 	}
 	spin_unlock_irqrestore(&dump_list_lock, flags);
 
@@ -3447,6 +3460,7 @@  int kmsg_dump_unregister(struct kmsg_dumper *dumper)
 		dumper->registered = 0;
 		list_del_rcu(&dumper->list);
 		err = 0;
+		num_dumpers--;
 	}
 	spin_unlock_irqrestore(&dump_list_lock, flags);
 	synchronize_rcu();