From: John Ogness <john.ogness@linutronix.de>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org, linux-parisc@vger.kernel.org
Subject: Re: [PATCH printk-rework 08/14] printk: add syslog_lock
Date: Fri, 19 Feb 2021 17:33:13 +0100 [thread overview]
Message-ID: <8735xs10hi.fsf@jogness.linutronix.de> (raw)
In-Reply-To: <875z2o15ha.fsf@jogness.linutronix.de>
Added CC: linux-parisc@vger.kernel.org
On 2021-02-19, John Ogness <john.ogness@linutronix.de> wrote:
>>> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
>>> index 20c21a25143d..401df370832b 100644
>>> --- a/kernel/printk/printk.c
>>> +++ b/kernel/printk/printk.c
>>> +/* Return a consistent copy of @syslog_seq. */
>>> +static u64 read_syslog_seq_irq(void)
>>> +{
>>> + u64 seq;
>>> +
>>> + raw_spin_lock_irq(&syslog_lock);
>>> + seq = syslog_seq;
>>> + raw_spin_unlock_irq(&syslog_lock);
>>
>> Is there any particular reason to disable interrupts here?
>>
>> It would make sense only when the lock could be taken in IRQ
>> context. Then we would need to always disable interrupts when
>> the lock is taken. And if it is taken in IRQ context, we would
>> need to safe flags.
>
> All other instances of locking @syslog_lock are done with interrupts
> disabled. And we have:
>
> register_console()
> logbuf_lock_irqsave()
> raw_spin_lock(&syslog_lock)
>
> I suppose I need to go through all the console drivers to see if any
> register in interrupt context. If not, that logbuf_lock_irqsave()
> should be replaced with logbuf_lock_irq(). And then locking
> @syslog_lock will not need to disable interrupts.
I found a possible call chain in interrupt context. From arch/parisc
there is the interrupt handler:
handle_interruption(code=1) /* High-priority machine check (HPMC) */
pdc_console_restart()
pdc_console_init_force()
register_console()
All other register_console() calls in the kernel are either during init
(within __init sections and probe functions) or are clearly not in
interrupt context (using mutex, kzalloc, spin_lock_irq, etc).
I am not familiar with parisc, but I am assuming handle_interruption()
is always called with interrupts disabled (unless the HPMC interrupt is
somehow an exception).
John Ogness
next prev parent reply other threads:[~2021-02-19 16:34 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-18 8:18 [PATCH printk-rework 00/14] printk: remove logbuf_lock John Ogness
2021-02-18 8:18 ` [PATCH printk-rework 01/14] printk: limit second loop of syslog_print_all John Ogness
2021-02-18 16:15 ` Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 02/14] printk: kmsg_dump: remove unused fields John Ogness
2021-02-18 16:18 ` Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 03/14] printk: refactor kmsg_dump_get_buffer() John Ogness
2021-02-18 8:18 ` [PATCH printk-rework 04/14] printk: consolidate kmsg_dump_get_buffer/syslog_print_all code John Ogness
2021-02-19 12:28 ` Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 05/14] printk: introduce CONSOLE_LOG_MAX for improved multi-line support John Ogness
2021-02-19 12:44 ` Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 06/14] printk: use seqcount_latch for clear_seq John Ogness
2021-02-18 8:18 ` [PATCH printk-rework 07/14] printk: use atomic64_t for devkmsg_user.seq John Ogness
2021-02-19 12:59 ` Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 08/14] printk: add syslog_lock John Ogness
2021-02-19 13:30 ` Petr Mladek
2021-02-19 14:45 ` John Ogness
2021-02-19 16:33 ` John Ogness [this message]
2021-02-21 21:39 ` Helge Deller
2021-02-22 16:28 ` Petr Mladek
2021-02-23 12:22 ` Helge Deller
2021-02-23 14:23 ` Petr Mladek
2021-02-23 14:45 ` Helge Deller
2021-02-22 16:05 ` Petr Mladek
2021-02-22 16:43 ` John Ogness
2021-02-23 14:38 ` Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 09/14] printk: introduce a kmsg_dump iterator John Ogness
2021-02-19 15:56 ` Petr Mladek
2021-02-19 16:50 ` Michael Kelley
2021-02-19 17:57 ` synchronization model: was: " Petr Mladek
2021-02-24 12:27 ` John Ogness
2021-02-24 15:40 ` John Ogness
2021-02-25 12:33 ` Petr Mladek
2021-02-26 8:36 ` John Ogness
2021-02-26 9:48 ` Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 10/14] um: synchronize kmsg_dumper John Ogness
2021-02-18 8:18 ` [PATCH printk-rework 11/14] printk: remove logbuf_lock John Ogness
2021-02-23 11:44 ` Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 12/14] printk: kmsg_dump: remove _nolock() variants John Ogness
2021-02-23 11:51 ` Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 13/14] printk: kmsg_dump: use kmsg_dump_rewind John Ogness
2021-02-23 11:53 ` Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 14/14] printk: console: remove unnecessary safe buffer usage John Ogness
2021-02-23 12:55 ` Petr Mladek
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