From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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,
Francesco Dolcini <francesco@dolcini.it>,
kernel test robot <oliver.sang@intel.com>
Subject: Re: [PATCH printk v3 02/14] printk: Adjust mapping for 32bit seq macros
Date: Mon, 15 Jan 2024 09:51:41 +0100 [thread overview]
Message-ID: <20240115085141.MSS4LLsR@linutronix.de> (raw)
In-Reply-To: <ZaGBlDTuQ0hYBpeJ@alley>
On 2024-01-12 19:14:44 [+0100], Petr Mladek wrote:
>
> That said, I am a bit nervous that a bug like this might cause
> workqueue stall and panic() the kernel.
> At least, this is how I read
> https://lore.kernel.org/oe-lkp/202311171611.78d41dbe-oliver.sang@intel.com/
well, workqueue stalls and RCU as well because the CPU spins. That is a
natural consequence because the CPU makes no progress (at boot). The
panic _might_ be due to panic_on_error or so.
There is no scheduler, nothing so one CPU is blocked and the world ends…
> It looks like it caused some loop and refcout overlow or so.
> But I might be wrong.
>
> I would like to better understand this and check if we could prevent
> it somehow.
Based on memory: the problem is that the sign extension bug (the fixed
bug) returned the wrong or too low sequence number. So the printk code
tried again to obtain a new sequence number. And got the wrong
again. And this is what looped during boot.
I'm not sure if this sort of lockup can happen now after the bug is
fixed. I can issue a NMI backtrace on all CPUs (32) without the sync (so
they all can printk immediately and not one after the other) and it
prints and continues…
> Best Regards,
> Petr
Sebastian
next prev parent reply other threads:[~2024-01-15 8:51 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-14 21:41 [PATCH printk v3 00/14] fix console flushing John Ogness
2023-12-14 21:41 ` [PATCH printk v3 01/14] printk: nbcon: Relocate 32bit seq macros John Ogness
2024-01-12 10:14 ` Petr Mladek
2023-12-14 21:41 ` [PATCH printk v3 02/14] printk: Adjust mapping for " John Ogness
2023-12-15 9:55 ` Sebastian Andrzej Siewior
2023-12-15 10:10 ` John Ogness
2023-12-15 10:58 ` Sebastian Andrzej Siewior
2024-01-12 10:28 ` Petr Mladek
2024-01-12 18:14 ` Petr Mladek
2024-01-15 8:51 ` Sebastian Andrzej Siewior [this message]
2024-01-15 10:52 ` John Ogness
2024-01-15 16:17 ` Petr Mladek
2024-01-15 17:08 ` John Ogness
2023-12-14 21:41 ` [PATCH printk v3 03/14] printk: Use prb_first_seq() as base " John Ogness
2024-01-12 16:19 ` Petr Mladek
2023-12-14 21:41 ` [PATCH printk v3 04/14] printk: ringbuffer: Do not skip non-finalized records with prb_next_seq() John Ogness
2024-01-12 18:05 ` Petr Mladek
2024-01-15 11:55 ` John Ogness
2024-01-15 17:00 ` Petr Mladek
2024-02-05 11:33 ` John Ogness
2024-02-06 17:27 ` Petr Mladek
2023-12-14 21:41 ` [PATCH printk v3 05/14] printk: ringbuffer: Clarify special lpos values John Ogness
2024-01-30 13:12 ` Petr Mladek
2023-12-14 21:41 ` [PATCH printk v3 06/14] printk: For @suppress_panic_printk check for other CPU in panic John Ogness
2023-12-14 21:41 ` [PATCH printk v3 07/14] printk: Add this_cpu_in_panic() John Ogness
2023-12-14 21:41 ` [PATCH printk v3 08/14] printk: ringbuffer: Cleanup reader terminology John Ogness
2024-01-30 14:36 ` Petr Mladek
2023-12-14 21:41 ` [PATCH printk v3 09/14] printk: Wait for all reserved records with pr_flush() John Ogness
2024-01-31 11:36 ` Petr Mladek
2024-02-05 13:33 ` John Ogness
2024-02-07 9:20 ` Petr Mladek
2023-12-14 21:41 ` [PATCH printk v3 10/14] printk: ringbuffer: Skip non-finalized records in panic John Ogness
2024-02-01 16:56 ` Petr Mladek
2023-12-14 21:41 ` [PATCH printk v3 11/14] printk: ringbuffer: Consider committed as finalized " John Ogness
2024-02-01 18:00 ` Petr Mladek
2024-02-05 14:08 ` John Ogness
2024-02-07 10:11 ` Petr Mladek
2023-12-14 21:41 ` [PATCH printk v3 12/14] printk: Disable passing console lock owner completely during panic() John Ogness
2023-12-14 21:42 ` [PATCH printk v3 13/14] printk: Avoid non-panic CPUs writing to ringbuffer John Ogness
2024-02-02 9:26 ` Petr Mladek
2023-12-14 21:42 ` [PATCH printk v3 14/14] panic: Flush kernel log buffer at the end John Ogness
2024-02-02 9:30 ` Petr Mladek
2024-02-02 9:38 ` [PATCH printk v3 00/14] fix console flushing Petr Mladek
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