From: Sergey Senozhatsky <senozhatsky@chromium.org>
To: Petr Mladek <pmladek@suse.com>
Cc: John Ogness <john.ogness@linutronix.de>,
Sergey Senozhatsky <senozhatsky@chromium.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH printk v2 2/5] printk: Add NMI safety to console_flush_on_panic() and console_unblank()
Date: Wed, 12 Jul 2023 01:07:58 +0900 [thread overview]
Message-ID: <20230711160758.GG12154@google.com> (raw)
In-Reply-To: <ZK14p-ocWuuHkSAQ@alley>
On (23/07/11 17:43), Petr Mladek wrote:
> On Mon 2023-07-10 15:51:21, John Ogness wrote:
> > The printk path is NMI safe because it only adds content to the
> > buffer and then triggers the delayed output via irq_work. If the
> > console is flushed or unblanked on panic (from NMI context) then it
> > can deadlock in down_trylock_console_sem() because the semaphore is
> > not NMI safe.
>
> <thinking loudly>
>
> Just to be sure. The semaphore is not NMI safe because even the
> trylock takes an internal spin lock. Am I right, please?
>
> Alternative solution would be to make down_trylock() NMI safe
> by using raw_spin_trylock_irqsave() for the internal lock.
>
> But this actually would not solve the whole problem. If the NMI safe
> down_trylock() succeeded then up() would need to be called
> in NMI as well. And up() really needs to take the spin lock
> which might get blocked in the meantime.
I guess another problem with up() is that it also may call
try_to_wake_up(), that may attempt to acquire a bunch of other
spin_lock-s.
next prev parent reply other threads:[~2023-07-11 16:08 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-10 13:45 [PATCH printk v2 0/5] various cleanups John Ogness
2023-07-10 13:45 ` [PATCH printk v2 1/5] kdb: do not assume write() callback available John Ogness
2023-07-11 0:25 ` Sergey Senozhatsky
2023-07-11 8:23 ` Daniel Thompson
2023-07-11 8:58 ` John Ogness
2023-07-11 9:01 ` Daniel Thompson
2023-07-10 13:45 ` [PATCH printk v2 2/5] printk: Add NMI safety to console_flush_on_panic() and console_unblank() John Ogness
2023-07-11 15:43 ` Petr Mladek
2023-07-11 16:07 ` Sergey Senozhatsky [this message]
2023-07-12 21:11 ` John Ogness
2023-07-13 14:43 ` Petr Mladek
2023-07-14 4:00 ` Sergey Senozhatsky
2023-07-14 9:41 ` Petr Mladek
2023-07-10 13:45 ` [PATCH printk v2 3/5] printk: Consolidate console deferred printing John Ogness
2023-07-11 15:17 ` Sergey Senozhatsky
2023-07-13 14:51 ` Petr Mladek
2023-07-10 13:45 ` [PATCH printk v2 4/5] printk: Add per-console suspended state John Ogness
2023-07-11 15:08 ` Sergey Senozhatsky
2023-07-11 15:23 ` John Ogness
2023-07-11 15:26 ` Sergey Senozhatsky
2023-07-11 15:30 ` Sergey Senozhatsky
2023-07-13 15:53 ` Petr Mladek
2023-07-10 13:45 ` [PATCH printk v2 5/5] printk: Rename abandon_console_lock_in_panic() to other_cpu_in_panic() John Ogness
2023-07-11 0:22 ` Sergey Senozhatsky
2023-07-13 15:55 ` Petr Mladek
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