Messages in this thread | | | Date | Tue, 28 Nov 2017 20:07:53 -0800 | From | Jakub Kicinski <> | Subject | Re: [PATCH] sched/deadline: fix one-bit signed bitfields to be unsigned |
| |
On Tue, 28 Nov 2017 12:36:19 -0800, Jeff Kirsher wrote: > From: Jacob Keller <jacob.e.keller@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.keller@intel.com> > Cc: luca abeni <luca.abeni@santannapisa.it> > Tested-by: Andrew Bowers <andrewx.bowers@intel.com> > Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@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.carpenter@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 <willy@infradead.org> Reported-by: Xin Long <lucien.xin@gmail.com> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com> Reviewed-by: Luca Abeni <luca.abeni@santannapisa.it> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: kernel-janitors@vger.kernel.org Cc: luca abeni <luca.abeni@santannapisa.it> Link: http://lkml.kernel.org/r/20171013070121.dzcncojuj2f4utij@mwanda Signed-off-by: Ingo Molnar <mingo@kernel.org>
| |