On (07/13/19 09:46), Konstantin Khlebnikov wrote:
> > On (07/12/19 17:54), Konstantin Khlebnikov wrote:
>
> Yep printk() can deal with NMI, but kmsg_dump() is a different beast.
> It reads printk buffer and saves content into persistent storage like ACPI
> ERST.
Ah, sorry! I misread your patch. Yeah, I see what you are doing.
OK. So, I guess that for kmsg_dump(KMSG_DUMP_PANIC) we should be
fine in general.
We call kmsg_dump(KMSG_DUMP_PANIC) after smp_send_stop() and after
printk_safe_flush_on_panic(). printk_safe_flush_on_panic() resets
the state of logbuf_lock, so logbuf_lock, in general case, should
be unlocked by the time we call kmsg_dump(KMSG_DUMP_PANIC).
Even for nested contexts.
CPU0
printk()
logbuf_lock_irqsave(flags)
-> NMI
panic()
smp_send_stop()
printk_safe_flush_on_panic()
raw_spin_lock_init(&logbuf_lock) << reinit >>
kmsg_dump(KMSG_DUMP_PANIC)
logbuf_lock_irqsave(flags) << expected to be OK >>
So do we have strong reasons to disable NMI->panic->kmsg_dump(DUMP_PANIC)?
Other kmsg_dump(), maybe, can experience some troubles sometimes,
need to check that.
-ss
