On 14/02/2023 11:46, Petr Mladek wrote:
[...]
My understanding is that it's a mechanism to prevent some concurrency, in case some other CPU modify this variable while panic() is running. I find it very unlikely, hence I removed it - but if people consider this copy needed, I can respin this patch and keep it, even providing a comment about that, in order to be explict about its need.
Yes, I think that it makes the behavior consistent even when the global variable manipulated in parallel.
I would personally prefer to keep the local copy. Better safe than sorry.
Hi Petr, thanks for your review! OK, we could keep this local copy, makes sense...even adding a comment, to make its purpose really clear.
[...] @@ -211,9 +211,6 @@ static void panic_print_sys_info(bool console_flush) return; }
- if (panic_print & PANIC_PRINT_ALL_CPU_BT)
trigger_all_cpu_backtrace();
Sigh, this is yet another PANIC_PRINT_ action that need special timing. We should handle both the same way.
What about the following? The parameter @mask says what actions are allowed at the given time. < ..code..>
I think your approach is interesting, it's very "organized".
But I think it's a bit conflicting with that purpose we had on notifiers refactor, to deprecate "bogus" usages of panic_print, as in https://lore.kernel.org/lkml/20220427224924.592546-26-gpiccoli@igalia.com/ .
So, the idea of my approach is to allow:
(a) Easy removal of panic_print_sys_info() of panic(), once we move it to a panic notifier;
(b) Better separate and identify the "bogus" cases. The CPU backtrace one is less a bogus case in my opinion, more a "complicated" one, since it's related with the CPUs stop routines. But the console flush, as we discussed, it's clearly something that calls for a new parameter (and such param was added in the refactor patch).
In the end, I think your approach is interesting but it's kinda like we're adding the fix to later, on refactor, entirely remove/rework it. With my approach we wouldn't be calling panic_print_sys_info() again (3rd time!) on panic(), and also would be more natural to move it later to a new panic notifier.
What you / others think? If your approach is in the end preferred, it's fine by me - I'd just ask you to submit as a full patch so we can get it merged as a fix in 6.3, if possible (and backport it to the 6.1/6.2 stable). Now, if my approach is fine, I can resubmit as a V5 keeping the local variable - lemme know.
Cheers,
Guilherme