On Tue, Mar 10, 2015 at 02:39:39PM +0000, Alexander Gordeev wrote:
> On Mon, Mar 09, 2015 at 09:43:18PM -0700, Paul E. McKenney wrote:
> > On Mon, Mar 09, 2015 at 04:49:43PM -0700, Paul E. McKenney wrote:
> > > On Mon, Mar 09, 2015 at 04:39:47PM -0700, Paul E. McKenney wrote:
> > > > On Mon, Mar 09, 2015 at 02:40:21PM -0700, Paul E. McKenney wrote:
> > > > > On Mon, Mar 09, 2015 at 09:34:04AM +0100, Alexander Gordeev wrote:
> > > > > > Hi Paul,
> > > > > >
> > > > > > Here is cleanup of RCU tree initialization rebased on linux-rcu
> > > > > > rcu/next
> > > > > > repo, as you requested. Please, note an extra patch #10 that was not
> > > > > > present in the first post.
> > > > > >
> > > > > > The series successfully passes kernel build test with
> > > > > > CONFIG_RCU_FANOUT
> > > > > > and CONFIG_RCU_FANOUT_LEAF equal to 5.
> > > > >
> > > > > I queued up 1-9, as discussed and have started testing. I will let
> > > > > you
> > > > > know how it goes.
> > > >
> > > > Initial testing went well except for the following warning:
> > > >
> > > > /home/paulmck/public_git/linux-rcu/kernel/rcu/tree.c: In function
> > > > ‘rcu_init_one.isra.63’:
> > > > /home/paulmck/public_git/linux-rcu/kernel/rcu/tree.c:3961:3: warning:
> > > > ‘levelcnt[0]’ may be used uninitialized in this function
> > > > [-Wmaybe-uninitialized]
> > > > for (j = 0; j < levelcnt[i]; j++, rnp++) {
> > > >
> > > > This warning looks like a false positive to me, given that the loop
> > > > near the beginning of the function initializes levelcnt[0]. Am I
> > > > missing something here, and either way, what is the best way to shut
> > > > this warning up?
> > >
> > > My suggestion is the following:
> > >
> > > if (rcu_num_lvls <= 0)
> > > panic("rcu_init_one: rcu_num_lvls underflow");
> > >
> > > Just following the other panic() in rcu_init_one().
> >
> > As in the following patch.
> >
> > Thanx, Paul
> >
> > ------------------------------------------------------------------------
> >
> > rcu: Shut up spurious gcc uninitialized-variable warning
> >
> > Because gcc doesn't realize that rcu_num_lvls must be strictly greater
> > than zero, some versions give a spurious warning about levelcnt[0] being
> > uninitialized in rcu_init_one(). This commit adds a panic() in that
> > case in order to educate gcc on this point.
> >
> > Signed-off-by: Paul E. McKenney <[email protected]>
> >
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index bd5a9a1db048..5b42d94335e3 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -3942,6 +3942,8 @@ static void __init rcu_init_one(struct rcu_state *rsp,
> > /* Silence gcc 4.8 warning about array index out of range. */
> > if (rcu_num_lvls > RCU_NUM_LVLS)
> > panic("rcu_init_one: rcu_num_lvls overflow");
> > + if (rcu_num_lvls <= 0)
> > + panic("rcu_init_one: rcu_num_lvls underflow");
>
> I believe '... else if (rcu_num_lvls <= 0)' is more appropriate here.
Good point.
> But do you think keeping two static strings just to shut the compiler
> worth it? May be a single complain would be enough?
As in the following?
if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
panic("rcu_init_one: rcu_num_lvls out of range");
For Tree RCU, I doubt that the memory size matters, but I do like
having two lines of code instead of four lines. I took this approach.
Thanx, Paul
> if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
> panic("rcu_init_one: rcu_num_lvls is out of range");
>
> > /* Initialize the level-tracking arrays. */
> >
> >
>
> --
> Regards,
> Alexander Gordeev
> [email protected]
>
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