linux-kernel - Re: [PATCH] printk: Fix discarding of records

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Date:	Sun, 16 Feb 2014 18:23:43 -0500
From:	"Banerjee, Debabrata" <dbanerje@...mai.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kay Sievers <kay.sievers@...y.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jeff Mahoney <jeffm@...e.com>,
	"dbavatar@...il.com" <dbavatar@...il.com>,
	"Hunt, Joshua" <johunt@...mai.com>, stable <stable@...r.kernel.org>
Subject: Re: [PATCH] printk: Fix discarding of records

On 2/16/14, 2:28 PM, "Linus Torvalds" <torvalds@...ux-foundation.org>
wrote:

>Why are *those* particular two "prev = msg->flags" incorrect, when
>every other case where we walk the messages they are required?
>
>The code/logic makes no sense. You remove the "prev = msg->flags" at
>line 1070, when the *identical* loop just above it has it. So now the
>two loops count the number of characters differently. That makes no
>sense.
>
>So I don't think this fixes the fundamental problem. I'm more inclined
>to believe that LOG_CONT is wrongly set somewhere, for example because
>a continuation wasn't actually originally printed due to coming from
>different users or something like that.
>
>Or at the very least I want a coherent explanation why one loop would
>do this and the other would not, and why counting up *different*
>numbers could possibly make sense.

The explanation is: the loops look identical but they are not. When a
record is printed first, its size can expand due to adding the prefix and
timestamp. The second loop is calculating len with the first line printed
possibly changing every iteration.


>
>Because as it is, there clearly is some problem, but the patch does
>not look sensible to me.

You are right, the patch is still flawed, sending V2.


-Debabrata

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