Hi Petr, first of all, I'd like to thank you for the _very_ complete and informative response, pretty useful! Some comments inline below: On 03/01/2022 11:58, Petr Mladek wrote: > [...] > I see the point. Unfortunately, there is some risk in this change > so I have to ask: > > Did you miss this behavior in practice? > Or does it just look like something that might be useful? Heh it's a valid question! And the answer is that indeed, we miss this behavior in practice - the plan is to use pstore as panic "fast" log collection (instead of kdump), and to print some extra info through panic_print. Hence the surprise when that information wasn't properly stored in the pstore saved logs... > [...] > Note that panic_print_sys_info() might produce a lot of lines. There is > non-trivial chance that a lot of information might get lost because > of the limited log buffer size. > > It might cause regression even when no dumpers are registered and > crash kernel is not loaded. panic_print_sys_info() might overwrite > the existing messages before we try hard to flush them via > console_flush_on_panic(). Sure, we already account for this risk, and make use of "log_buf_len" to increase dmesg size, something like 4M/8M. Now, the second portion of your statement is a bit frightening! Maybe a silly question, but the risk is to lose some messages in the *dmesg* or only in the output console, like a serial/graphic console? If the risk is to lose messages even in the dmesg (that is going to be collected through pstore/any other kmsg dumper), do you think would make sense to have a second (in fact, first!) "console_flush_on_panic(...)" _before_ "panic_print_sys_info()"? What would be the cons in this approach? I understand that we may need to (at least) disable debug_locks earlier than it's currently done, for example. If kexec is more risky having this earlier flush, we could flush conditionally on not having a crash kernel loaded. > [...] > IMHO, the best solution would be to allow dumping messages produced > by panic_print_sys_info() using the registered dumpers directly. > But it might require redesigning the kmsg_dump API. > > > After all, the proposed patch might be good enough. > panic_print_sys_info() does nothing by default. > It might be enough to document that a large enough log buffer > should be used when some output is enabled, especially when > a dumper is used. > > Also we should mention these pitfalls and risks in the commit > message. OK, makes total sense. I'll wait on your feedback to my points above, and maybe others could also provide ideas/concerns, and then, I'll rework the commit message/code accordingly. Thanks again, and a happy new year to you and family =) Cheers, Guilherme _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
