linux-kernel - Re: [PATCH 0/2] printk: replace ringbuffer

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Date:   Fri, 07 Feb 2020 08:43:39 +0100
From:   John Ogness <john.ogness@...utronix.de>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        lijiang <lijiang@...hat.com>, Petr Mladek <pmladek@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrea Parri <parri.andrea@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] printk: replace ringbuffer

On 2020-02-07, Steven Rostedt <rostedt@...dmis.org> wrote:
>> The quick fixup:
>> 
>> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
>> index d0d24ee1d1f4..5ad67ff60cd9 100644
>> --- a/kernel/printk/printk.c
>> +++ b/kernel/printk/printk.c
>> @@ -883,6 +883,7 @@ static int devkmsg_open(struct inode *inode, struct file *file)
>>  	user->record.text_buf_size = sizeof(user->text_buf);
>>  	user->record.dict_buf = &user->dict_buf[0];
>>  	user->record.dict_buf_size = sizeof(user->dict_buf);
>> +	user->record.text_line_count = NULL;
>>  
>>  	logbuf_lock_irq();
>>  	user->seq = prb_first_seq(prb);
>
> FYI, I used your patch set to test out Konstantin's new get-lore-mbox
> script, and then applied them. It locked up on boot up as well, and
> applying this appears to fix it.

Yes, this is a horrible bug. In preparation for my v2 I implemented:

    prb_rec_init_rd()
    prb_rec_init_wr()

as static inline functions to initialize the records. There is a reader
and writer variant because they initialize the records differently:
readers provide buffers, writers request buffers. This eliminates the
manual twiddling with the record struct and ensures that the struct is
always properly initialized.

John Ogness