On (20/07/19 11:27), Linus Torvalds wrote:
> On Sun, Jul 19, 2020 at 7:35 AM Sergey Senozhatsky
> <sergey.senozhatsky@xxxxxxxxx> wrote:
> >
> > Can we merge lines that we don't want to merge?
> >
> > pr_cont() -> IRQ -> pr_cont() -> NMI -> pr_cont()
>
> That pr_cont in either IRQ or NMI context would be a bug.
>
> You can't validly have a PR_CONT without the non-cont that precedes it.
Do I get it right, what you are saying is - when we process a PR_CONT
message the cont buffer should already contain previous non-LOG_NEWLINE
and non-PR_CONT message, otherwise it's a bug?
lockdep (I'll trim the code)
static void __print_lock_name(struct lock_class *class)
{
..
name = class->name;
if (!name) {
name = __get_key_name(class->key, str);
printk(KERN_CONT "%s", name);
} else {
printk(KERN_CONT "%s", name);
if (class->name_version > 1)
printk(KERN_CONT "#%d", class->name_version);
if (class->subclass)
printk(KERN_CONT "/%d", class->subclass);
}
}
static void print_lock_name(struct lock_class *class)
{
printk(KERN_CONT " (");
__print_lock_name(class);
printk(KERN_CONT "){%s}-{%hd:%hd}", usage, ...
}
static void
print_bad_irq_dependency(struct task_struct *curr,
{
..
pr_warn("which would create a new lock dependency:\n");
print_lock_name(hlock_class(prev));
pr_cont(" ->");
print_lock_name(hlock_class(next));
pr_cont("\n");
..
}
pr_warn() is LOG_NEWLINE, so cont buffer is empty by the time
we call print_lock_name()->__print_lock_name(), which do several
pr_cont() print outs.
I'm quite sure there is more code that does similar things.
But, overall, isn't it by design that we can process pr_cont()
message with no preceding non-cont message? Because of preliminary
flushes. Example:
CPU0
pr_info("foo"); // !LOG_NEWLINE goes into the cont buffer
pr_cont("1"); // OK
-> IRQ / NMI / exception / etc
pr_alert("error\n"); // flush cont buffer, log_store error message (it's LOG_NEWLINE)
<- iret
pr_cont("2"); // cont buffer was flushed. There is no preceding non-cont message
pr_cont("3");
pr_cont("\n");
Or am I misunderstanding what you saying?
-ss
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