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| author | Steven Rostedt <srostedt@redhat.com> | 2011-03-25 16:21:06 -0400 |
|---|---|---|
| committer | Steven Rostedt <rostedt@goodmis.org> | 2011-03-28 10:10:42 -0400 |
| commit | ccd0d44fad38dc1bb4b26dcc7a30e9f2c3b36870 (patch) | |
| tree | 4b3953b84fffb65bdf7b54955aed40d45d538e4a /include | |
| parent | 18bcd0c8cb7d85a9063b88ec810dc1cdc0974518 (diff) | |
| download | linux-stable-ccd0d44fad38dc1bb4b26dcc7a30e9f2c3b36870.tar.gz linux-stable-ccd0d44fad38dc1bb4b26dcc7a30e9f2c3b36870.tar.bz2 linux-stable-ccd0d44fad38dc1bb4b26dcc7a30e9f2c3b36870.zip | |
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>
Diffstat (limited to 'include')
| -rw-r--r-- | include/asm-generic/bug.h | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h index f2d2faf4d9ae..e5a3f5880001 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 |