linux-kernel - Re: [PATCH v5 3/4] kdb: Make kdb_printf() console handling more robust

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Message-ID: <20200603081025.GC14855@linux-b0ei>
Date:   Wed, 3 Jun 2020 10:10:26 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Sumit Garg <sumit.garg@...aro.org>
Cc:     daniel.thompson@...aro.org, kgdb-bugreport@...ts.sourceforge.net,
        jason.wessel@...driver.com, dianders@...omium.org,
        sergey.senozhatsky@...il.com, gregkh@...uxfoundation.org,
        jslaby@...e.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/4] kdb: Make kdb_printf() console handling more
 robust

On Wed 2020-06-03 12:52:14, Sumit Garg wrote:
> While rounding up CPUs via NMIs, its possible that a rounded up CPU
> maybe holding a console port lock leading to kgdb master CPU stuck in
> a deadlock during invocation of console write operations. A similar
> deadlock could also be possible while using synchronous breakpoints.
> 
> So in order to avoid such a deadlock, set oops_in_progress to encourage
> the console drivers to disregard their internal spin locks: in the
> current calling context the risk of deadlock is a bigger problem than
> risks due to re-entering the console driver. We operate directly on
> oops_in_progress rather than using bust_spinlocks() because the calls
> bust_spinlocks() makes on exit are not appropriate for this calling
> context.
> 
> Suggested-by: Petr Mladek <pmladek@...e.com>

I think that this was actually suggested by Sergey.

> Signed-off-by: Sumit Garg <sumit.garg@...aro.org>
> Reviewed-by: Douglas Anderson <dianders@...omium.org>

Otherwise, it looks good. With updated suggested by:

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr