Re: [PATCH] kcsan: Don't flush the consoles while holding report_lock

[John Ogness]

On 2026-11-03, Breno Leitao <leitao@xxxxxxxxxx> wrote:
> Since commit 59cd94ef8009 ("lockdep: Mark emergency sections in lockdep
> splats"), print_irqtrace_events() runs inside an nbcon emergency
> section. In an emergency section, every printk() flushes all pending
> records to the nbcon consoles from the calling context (instead of the
> printk thread).
>
> With CONFIG_KCSAN_VERBOSE, print_report() calls print_irqtrace_events()
> while holding the raw report_lock with interrupts disabled, so every
> verbose report writes out the whole console backlog under report_lock,
> as consoles/UARTs are usually slow, this is not good.

I am fine with this patch, but am not happy about the motivation. You
are right that it is "not good", but it is "not good" because the CPU is
being put into an emergency state when it is not really an
emergency. Even if the report_lock was not being held, this patch would
be equally valid.

I would even say this patch fixes 59cd94ef8009 because
print_irqtrace_events() is not exclusively used for lockdep splats.

John