On Tue, 28 Nov 2017 12:36:19 -0800, Jeff Kirsher wrote:
> From: Jacob Keller <jacob.e.kel...@intel.com>
>
> Commit 799ba82de01e ("sched/deadline: Use C bitfields for the state
> flags", 2017-10-10) introduced the use of C bitfields for these
> variables. However, sparse complains about them:
>
> ./include/linux/sched.h:476:62: error: dubious one-bit signed bitfield
> ./include/linux/sched.h:477:62: error: dubious one-bit signed bitfield
> ./include/linux/sched.h:478:62: error: dubious one-bit signed bitfield
> ./include/linux/sched.h:479:62: error: dubious one-bit signed bitfield
>
> This is because a one-bit signed bitfield can only hold the values 0 and
> -1, which can cause problems if the program expects to be able to
> represent the value positive 1.
>
> In practice, this may not cause a bug since -1 would be considered
> "true" in logical tests, however we should avoid the practice anyways.
>
> Fixes: 799ba82de01e ("sched/deadline: Use C bitfields for the state flags",
> 2017-10-10)
> Signed-off-by: Jacob Keller <jacob.e.kel...@intel.com>
> Cc: luca abeni <luca.ab...@santannapisa.it>
> Tested-by: Andrew Bowers <andrewx.bow...@intel.com>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirs...@intel.com>
This is already in Linus's tree (I've been waiting for it to land as
well :))
commit aa5222e92f8000ed3c1c38dddf11c83222aadfb3
Author: Dan Carpenter <dan.carpen...@oracle.com>
Date: Fri Oct 13 10:01:22 2017 +0300
sched/deadline: Don't use dubious signed bitfields
It doesn't cause a run-time bug, but these bitfields should be unsigned.
When it's signed ->dl_throttled is set to either 0 or -1, instead of
0 and 1 as expected.
The sched.h file is included into tons of places so Sparse generates
a flood of warnings like this:
./include/linux/sched.h:477:54: error: dubious one-bit signed bitfield
Reported-by: Matthew Wilcox <wi...@infradead.org>
Reported-by: Xin Long <lucien....@gmail.com>
Signed-off-by: Dan Carpenter <dan.carpen...@oracle.com>
Reviewed-by: Luca Abeni <luca.ab...@santannapisa.it>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: kernel-janit...@vger.kernel.org
Cc: luca abeni <luca.ab...@santannapisa.it>
Link: http://lkml.kernel.org/r/20171013070121.dzcncojuj2f4utij@mwanda
Signed-off-by: Ingo Molnar <mi...@kernel.org>
