linux-kernel - [RFC PATCH v4 5/9] printk-rb: remove extra data buffer size allocation

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Message-Id: <20190807222634.1723-6-john.ogness@linutronix.de>
Date:   Thu,  8 Aug 2019 00:32:30 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Brendan Higgins <brendanhiggins@...gle.com>
Subject: [RFC PATCH v4 5/9] printk-rb: remove extra data buffer size allocation

The buffer for the raw data storage included extra space at the
end for a long. This was meant to guarantee space for the ID of a
wrapping datablock. However, since datablocks are padded and the
dataring is implemented such that no datablock can end at exactly
the end of the data buffer:
	 DATA_WRAPS(begin) != DATA_WRAPS(next)
there will always be space available for the ID of a wrapping
datablock.

Signed-off-by: John Ogness <john.ogness@...utronix.de>
---
 kernel/printk/ringbuffer.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/printk/ringbuffer.h b/kernel/printk/ringbuffer.h
index 462b4d3a3ee2..698d2328ea9e 100644
--- a/kernel/printk/ringbuffer.h
+++ b/kernel/printk/ringbuffer.h
@@ -175,8 +175,7 @@ struct dr_desc *prb_getdesc(unsigned long id, void *arg);
  * * descriptor 1 will be the next descriptor
  */
 #define DECLARE_PRINTKRB(name, avgdatabits, descbits)			\
-char _##name##_data[(1 << ((avgdatabits) + (descbits))) +		\
-				 sizeof(long)]				\
+char _##name##_data[1 << ((avgdatabits) + (descbits))]			\
 	__aligned(__alignof__(long));					\
 struct prb_desc _##name##_descs[1 << (descbits)] = {			\
 		{							\
-- 
2.20.1