Messages in this thread Patch in this message | | | Subject | [PATCH v2][GIT PULL] WARN_ON_SMP(): Add comment to explain ({0;}) | From | Steven Rostedt <> | Date | Mon, 28 Mar 2011 10:35:56 -0400 |
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Ingo,
As there were conflicts with the first version, I rebased on top of Linus's latest tree. It's just a comment change so I doubt this would cause any harm wrt rebasing.
-- Steve
Please pull the latest tip/futex/devel-2 tree, which can be found at:
git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-rt.git tip/futex/devel-2
Steven Rostedt (1): WARN_ON_SMP(): Add comment to explain ({0;})
---- include/asm-generic/bug.h | 7 +++++++ 1 files changed, 7 insertions(+), 0 deletions(-) --------------------------- commit ccd0d44fad38dc1bb4b26dcc7a30e9f2c3b36870 Author: Steven Rostedt <srostedt@redhat.com> Date: Fri Mar 25 16:21:06 2011 -0400
WARN_ON_SMP(): Add comment to explain ({0;}) The define to use ({0;}) for the !CONFIG_SMP case of WARN_ON_SMP() can be confusing. As the WARN_ON_SMP() needs to be a nop when CONFIG_SMP is not set, including all its parameters must not be evaluated, and that it must work as both a stand alone statement and inside an if condition, we define it to a funky ({0;}). A simple "0" will not work as it causes gcc to give the warning that the statement has no effect. As this strange definition has raised a few eyebrows from some major kernel developers, it is wise to document why we create such a work of art. Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Alexey Dobriyan <adobriyan@gmail.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h index f2d2faf..e5a3f58 100644 --- a/include/asm-generic/bug.h +++ b/include/asm-generic/bug.h @@ -194,6 +194,13 @@ extern void warn_slowpath_null(const char *file, const int line); #ifdef CONFIG_SMP # define WARN_ON_SMP(x) WARN_ON(x) #else +/* + * Use of ({0;}) because WARN_ON_SMP(x) may be used either as + * a stand alone line statement or as a condition in an if () + * statement. + * A simple "0" would cause gcc to give a "statement has no effect" + * warning. + */ # define WARN_ON_SMP(x) ({0;}) #endif
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