linux-kernel - Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount

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Date:	Sun, 1 Sep 2013 07:10:08 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	George Spelvin <linux@...izon.com>
Cc:	torvalds@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk,
	waiman.long@...com, Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless
 update of refcount

Speaking of bool (and I'm not a fan of it either), is this warning
just noise (which is bad enough since it masks real warnings), or is
this going to cause serious problems?

  CHECK   /usr/projects/linux/ext4/kernel/trace/trace.c
/usr/projects/linux/ext4/kernel/trace/trace.c:559:6: warning: symbol 'free_snapshot' was not declared. Should it be static?
/usr/projects/linux/ext4/kernel/trace/trace.c:1489:14: warning: expression using sizeof bool
/usr/projects/linux/ext4/kernel/trace/trace.c:1489:14: warning: expression using sizeof bool
/usr/projects/linux/ext4/kernel/trace/trace.c:1489:14: warning: expression using sizeof bool
/usr/projects/linux/ext4/kernel/trace/trace.c:1489:14: warning: expression using sizeof bool
/usr/projects/linux/ext4/kernel/trace/trace.c:1492:9: warning: expression using sizeof bool
/usr/projects/linux/ext4/kernel/trace/trace.c:1492:9: warning: expression using sizeof bool
/usr/projects/linux/ext4/kernel/trace/trace.c:1492:9: warning: expression using sizeof bool
/usr/projects/linux/ext4/kernel/trace/trace.c:1492:9: warning: expression using sizeof bool
/usr/projects/linux/ext4/kernel/trace/trace.c:1539:9: warning: expression using sizeof bool
/usr/projects/linux/ext4/kernel/trace/trace.c:1539:9: warning: expression using sizeof bool
/usr/projects/linux/ext4/kernel/trace/trace.c:1539:9: warning: expression using sizeof bool
/usr/projects/linux/ext4/kernel/trace/trace.c:1539:9: warning: expression using sizeof bool

(i.e., is a C compiler allowed to pack multiple bools stored in a data
structure into a single byte, with potentially hilarious results for C
code trying to do magic utilizing sizeof and offsetof (which some of
our kernel macros do use, IIRC)?

				- Ted

P.S.  BTW, this is not the only set of sparse warnings that are
emitted by files in kernel/trace/*; maybe it would be good if the
ftrace maintianers worked on nuking them all?  There are also a bunch
of warnings like which I've only recently learned indicated potential
RCU bugs:

/usr/projects/linux/ext4/kernel/trace/trace.c:1885:17: warning: incorrect type in assignment (different address spaces)
/usr/projects/linux/ext4/kernel/trace/trace.c:1885:17:    expected struct trace_buffer_struct *buffers
/usr/projects/linux/ext4/kernel/trace/trace.c:1885:17:    got struct trace_buffer_struct [noderef] <asn:3>*<noident>
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