| Message ID | 20220427224924.592546-15-gpiccoli@igalia.com (mailing list archive) |
|---|---|
| State | Handled Elsewhere |
| Headers | show |
| Series | The panic notifiers refactor | expand |
On Wed 2022-04-27 19:49:08, Guilherme G. Piccoli wrote: > The notifiers infrastructure provides a way to pass an "id" to the > callbacks to determine what kind of event happened, i.e., what is > the reason behind they getting called. > > The panic notifier currently pass 0, but this is soon to be > used in a multi-targeted notifier, so let's pass a meaningful > "id" over there. > > Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com> > --- > include/linux/panic_notifier.h | 5 +++++ > kernel/panic.c | 2 +- > 2 files changed, 6 insertions(+), 1 deletion(-) > > diff --git a/include/linux/panic_notifier.h b/include/linux/panic_notifier.h > index 41e32483d7a7..07dced83a783 100644 > --- a/include/linux/panic_notifier.h > +++ b/include/linux/panic_notifier.h > @@ -9,4 +9,9 @@ extern struct atomic_notifier_head panic_notifier_list; > > extern bool crash_kexec_post_notifiers; > > +enum panic_notifier_val { > + PANIC_UNUSED, > + PANIC_NOTIFIER = 0xDEAD, > +}; 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
On 10/05/2022 12:16, Petr Mladek wrote: > [...] > 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)? 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. IIUIC, this is more or less what I'm doing, but extending the idea for panic notifiers. Again, as a personal preference, it makes sense to me using id's VS comparing pointers to differentiate events/callers. Cheers, Guilherme
On Tue 2022-05-10 13:16:54, Guilherme G. Piccoli wrote: > On 10/05/2022 12:16, Petr Mladek wrote: > > [...] > > 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
On 17/05/2022 10:11, Petr Mladek wrote: > [...] >> 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): > > [... snip ...] > 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. > Hi Petr, thanks for the examples - I agree with you. In the end, seems I'm kind of abusing the API. This id is used to distinguish different situations in which the callback is called, but in the same "realm"/notifier list. In my case I have different list calling the same callback and (ab-)using the id to make distinction. I can rework the patches using pointer comparison, it's fine =) So, I'll drop this patch in V2. > 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. > OK, I'll re-work that patch - there's more there to be changed, that one is complex heheh Cheers!
diff --git a/include/linux/panic_notifier.h b/include/linux/panic_notifier.h index 41e32483d7a7..07dced83a783 100644 --- a/include/linux/panic_notifier.h +++ b/include/linux/panic_notifier.h @@ -9,4 +9,9 @@ extern struct atomic_notifier_head panic_notifier_list; extern bool crash_kexec_post_notifiers; +enum panic_notifier_val { + PANIC_UNUSED, + PANIC_NOTIFIER = 0xDEAD, +}; + #endif /* _LINUX_PANIC_NOTIFIERS_H */ diff --git a/kernel/panic.c b/kernel/panic.c index eb4dfb932c85..523bc9ccd0e9 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -287,7 +287,7 @@ void panic(const char *fmt, ...) * Run any panic handlers, including those that might need to * add information to the kmsg dump output. */ - atomic_notifier_call_chain(&panic_notifier_list, 0, buf); + atomic_notifier_call_chain(&panic_notifier_list, PANIC_NOTIFIER, buf); panic_print_sys_info(false);
The notifiers infrastructure provides a way to pass an "id" to the callbacks to determine what kind of event happened, i.e., what is the reason behind they getting called. The panic notifier currently pass 0, but this is soon to be used in a multi-targeted notifier, so let's pass a meaningful "id" over there. Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com> --- include/linux/panic_notifier.h | 5 +++++ kernel/panic.c | 2 +- 2 files changed, 6 insertions(+), 1 deletion(-)