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,
Miquel Raynal <miquel.raynal@bootlin.com>,
Richard Weinberger <richard@nod.at>,
Vignesh Raghavendra <vigneshr@ti.com>,
linux-mtd@lists.infradead.org
Subject: Re: [PATCH next v3 02/15] mtd: mtdoops: synchronize kmsg_dumper
Date: Tue, 02 Mar 2021 11:45:27 +0100 [thread overview]
Message-ID: <87tuptq1fc.fsf@jogness.linutronix.de> (raw)
In-Reply-To: <YDzaYqrk3Dv37uDa@alley>
On 2021-03-01, Petr Mladek <pmladek@suse.com> wrote:
>> The kmsg_dumper can be called from any context and CPU, possibly
>> from multiple CPUs simultaneously. Since the writing of the buffer
>> can occur from a later scheduled work queue, the oops buffer must
>> be protected against simultaneous dumping.
>>
>> Use an atomic bit to mark when the buffer is protected. Release the
>> protection in between setting the buffer and the actual writing in
>> order for a possible panic (immediate write) to be written during
>> the scheduling of a previous oops (delayed write).
>
> Just to be sure. You did not use spin lock to prevent problems
> with eventual double unlock in panic(). Do I get it correctly,
> please?
I do not understand what possible double unlock you are referring to.
I chose not to use spinlocks because I wanted something that does not
cause any scheduling or preemption side-effects for mtd. The mtd dumper
sometimes dumps directly, sometimes delayed (via scheduled work), and
they use different mtd callbacks in different contexts.
mtd_write() expects to be called in a non-atomic context. The callbacks
can take a mutex.
John Ogness
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http://lists.infradead.org/mailman/listinfo/linux-mtd/
next prev parent reply other threads:[~2021-03-03 21:57 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-25 20:24 [PATCH next v3 00/15] printk: remove logbuf_lock John Ogness
2021-02-25 20:24 ` [PATCH next v3 02/15] mtd: mtdoops: synchronize kmsg_dumper John Ogness
2021-03-01 12:13 ` Petr Mladek
2021-03-02 10:45 ` John Ogness [this message]
2021-03-02 12:48 ` Petr Mladek
2021-02-25 20:24 ` [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator John Ogness
2021-02-25 21:59 ` Kees Cook
2021-02-26 7:59 ` John Ogness
2021-03-01 18:07 ` Petr Mladek
2021-03-02 13:20 ` John Ogness
2021-03-02 13:55 ` Petr Mladek
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