[lustre-devel] [PATCH] staging: lustre: Move assignments out of function calls.

[Elise Lennion <elise.lennion@gmail.com>]

On Fri, Oct 21, 2016 at 10:34:53PM +0000, Dilger, Andreas wrote:
> On Oct 21, 2016, at 16:14, Elise Lennion <elise.lennion@gmail.com> wrote:
> > 
> > Assignments inside of function calls confuse the reader and should be
> > avoided, so they were moved out before the call.
> 
> Thanks for your patch.  I agree that this kind of usage is bad and avoid
> it in my own code and try to remove it when I see it.  However, in some
> cases it is needed to simplify the code flow (e.g. in conditionals that
> would otherwise need to duplicate logic).
> 
> More comments below.
> 
> > Found with Coccinelle, semantic patch:
> > @@
> > identifier f;
> > expression e1, e2;
> > assignment operator a;
> > @@
> > 
> > + e1 a e2;
> > f(...,
> > - (e1 a e2)
> > + e1
> > ,...);
> > 
> > Signed-off-by: Elise Lennion <elise.lennion@gmail.com>
> > ---
> > drivers/staging/lustre/lustre/ldlm/ldlm_lockd.c | 5 ++---
> > drivers/staging/lustre/lustre/llite/vvp_io.c    | 3 ++-
> > 2 files changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/staging/lustre/lustre/ldlm/ldlm_lockd.c b/drivers/staging/lustre/lustre/ldlm/ldlm_lockd.c
> > index 12647af..ec7f2a8 100644
> > --- a/drivers/staging/lustre/lustre/ldlm/ldlm_lockd.c
> > +++ b/drivers/staging/lustre/lustre/ldlm/ldlm_lockd.c
> > @@ -764,9 +764,8 @@ static int ldlm_bl_thread_main(void *arg)
> > 
> > 		if (!blwi) {
> > 			atomic_dec(&blp->blp_busy_threads);
> > -			l_wait_event_exclusive(blp->blp_waitq,
> > -					       (blwi = ldlm_bl_get_work(blp)),
> > -					       &lwi);
> > +			blwi = ldlm_bl_get_work(blp);
> > +			l_wait_event_exclusive(blp->blp_waitq, blwi, &lwi);
> 
> This first change is broken, since l_wait_event_exclusive() is actually a
> macro that is waiting until ldlm_bl_get_work() returns a work item.  Moving
> the blwi assignment before the wait means that this will wait forever.
> 
> This can be ignored for now, as there is a patch in the pipeline to clean
> up this code (http://review.whamcloud.com/5843) that James should be
> getting close to pushing, and it removes this inline assignment.
> 
> > 			busy = atomic_inc_return(&blp->blp_busy_threads);
> > 		} else {
> > 			busy = atomic_read(&blp->blp_busy_threads);
> > diff --git a/drivers/staging/lustre/lustre/llite/vvp_io.c b/drivers/staging/lustre/lustre/llite/vvp_io.c
> > index 1a4b897..87fdab2 100644
> > --- a/drivers/staging/lustre/lustre/llite/vvp_io.c
> > +++ b/drivers/staging/lustre/lustre/llite/vvp_io.c
> > @@ -450,7 +450,8 @@ static void vvp_io_advance(const struct lu_env *env,
> > 	struct vvp_io	 *vio = cl2vvp_io(env, ios);
> > 	CLOBINVRNT(env, obj, vvp_object_invariant(obj));
> > 
> > -	iov_iter_reexpand(vio->vui_iter, vio->vui_tot_count  -= nob);
> > +	vio->vui_tot_count -= nob;
> > +	iov_iter_reexpand(vio->vui_iter, vio->vui_tot_count);
> 
> This one is fine.  Please resubmit the patch with just this change.  You
> can add "Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>" for that
> patch.
> 
> Cheers, Andreas
> 
> > }
> > 
> > static void vvp_io_update_iov(const struct lu_env *env,
> > -- 
> > 2.7.4
> > 
> 

Sorry for the confusion with the macro usage, I'll send a v2 without
this undesired change.

thank you all for the detailed answer,

elise