On Tue 2022-05-10 13:16:54, Guilherme G. Piccoli wrote:

On 10/05/2022 12:16, Petr Mladek wrote:

quoted

[...]
Hmm, this looks like a hack. PANIC_UNUSED will never be used.
All notifiers will be always called with PANIC_NOTIFIER.

The @val parameter is normally used when the same notifier_list
is used in different situations.

But you are going to use it when the same notifier is used
in more lists. This is normally distinguished by the @nh
(atomic_notifier_head) parameter.

IMHO, it is a bad idea. First, it would confuse people because
it does not follow the original design of the parameters.
Second, the related code must be touched anyway when
the notifier is moved into another list so it does not
help much.

Or do I miss anything, please?

Best Regards,
Petr

Hi Petr, thanks for the review.

I'm not strong attached to this patch, so we could drop it and refactor
the code of next patches to use the @nh as identification - but
personally, I feel this parameter could be used to identify the list
that called such function, in other words, what is the event that
triggered the callback. Some notifiers are even declared with this
parameter called "ev", like the event that triggers the notifier.


You mentioned 2 cases:

(a) Same notifier_list used in different situations;

(b) Same *notifier callback* used in different lists;

Mine is case (b), right? Can you show me an example of case (a)?

There are many examples of case (a):

   + module_notify_list:
	MODULE_STATE_LIVE, 	/* Normal state. */
	MODULE_STATE_COMING,	/* Full formed, running module_init. */
	MODULE_STATE_GOING,	/* Going away. */
	MODULE_STATE_UNFORMED,	/* Still setting it up. */


   + netdev_chain:

	NETDEV_UP	= 1,	/* For now you can't veto a device up/down */
	NETDEV_DOWN,
	NETDEV_REBOOT,		/* Tell a protocol stack a network interface
				   detected a hardware crash and restarted
				   - we can use this eg to kick tcp sessions
				   once done */
	NETDEV_CHANGE,		/* Notify device state change */
	NETDEV_REGISTER,
	NETDEV_UNREGISTER,
	NETDEV_CHANGEMTU,	/* notify after mtu change happened */
	NETDEV_CHANGEADDR,	/* notify after the address change */
	NETDEV_PRE_CHANGEADDR,	/* notify before the address change */
	NETDEV_GOING_DOWN,
	...

    + vt_notifier_list:

	#define VT_ALLOCATE		0x0001 /* Console got allocated */
	#define VT_DEALLOCATE		0x0002 /* Console will be deallocated */
	#define VT_WRITE		0x0003 /* A char got output */
	#define VT_UPDATE		0x0004 /* A bigger update occurred */
	#define VT_PREWRITE		0x0005 /* A char is about to be written to the console */

    + die_chain:

	DIE_OOPS = 1,
	DIE_INT3,
	DIE_DEBUG,
	DIE_PANIC,
	DIE_NMI,
	DIE_DIE,
	DIE_KERNELDEBUG,
	...

These all call the same list/chain in different situations.
The situation is distinguished by @val.

You can see in the following patches (or grep the kernel) that people are using
this identification parameter to determine which kind of OOPS trigger
the callback to condition the execution of the function to specific
cases.

Could you please show me some existing code for case (b)?
I am not able to find any except in your patches.

Anyway, the solution in 16th patch is bad, definitely.
hv_die_panic_notify_crash() uses "val" to disinguish
both:

     + "panic_notifier_list" vs "die_chain"
     + die_val when callen via "die_chain"

The API around "die_chain" API is not aware of enum panic_notifier_val
and the API using "panic_notifier_list" is not aware of enum die_val.
As I said, it is mixing apples and oranges and it is error prone.

Best Regards,
Petr