linux-kernel - Re: [PATCH] xen/gntdev: fix up blockable calls to mn_invl_range

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Message-ID: <20180823135151.GM29735@dhcp22.suse.cz>
Date:   Thu, 23 Aug 2018 15:51:51 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        xen-devel@...ts.xenproject.org,
        LKML <linux-kernel@...r.kernel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH] xen/gntdev: fix up blockable calls to mn_invl_range_start

On Thu 23-08-18 22:44:07, Tetsuo Handa wrote:
> On 2018/08/23 21:07, Michal Hocko wrote:
> > diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> > index 57390c7666e5..e7d8bb1bee2a 100644
> > --- a/drivers/xen/gntdev.c
> > +++ b/drivers/xen/gntdev.c
> > @@ -519,21 +519,20 @@ static int mn_invl_range_start(struct mmu_notifier *mn,
> >  	struct gntdev_grant_map *map;
> >  	int ret = 0;
> >  
> > -	/* TODO do we really need a mutex here? */
> >  	if (blockable)
> >  		mutex_lock(&priv->lock);
> >  	else if (!mutex_trylock(&priv->lock))
> >  		return -EAGAIN;
> >  
> >  	list_for_each_entry(map, &priv->maps, next) {
> > -		if (in_range(map, start, end)) {
> > +		if (!blockable && in_range(map, start, end)) {
> 
> This still looks strange. Prior to 93065ac753e4, in_range() test was
> inside unmap_if_in_range(). But this patch removes in_range() test
> if blockable == true. That is, unmap_if_in_range() will unconditionally
> unmap if blockable == true, which seems to be an unexpected change.

You are right. I completely forgot I've removed in_range there. Does
this look any better?

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index e7d8bb1bee2a..30f81004ea63 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -525,14 +525,20 @@ static int mn_invl_range_start(struct mmu_notifier *mn,
 		return -EAGAIN;
 
 	list_for_each_entry(map, &priv->maps, next) {
-		if (!blockable && in_range(map, start, end)) {
+		if (in_range(map, start, end)) {
+			if (blockable)
+				continue;
+
 			ret = -EAGAIN;
 			goto out_unlock;
 		}
 		unmap_if_in_range(map, start, end);
 	}
 	list_for_each_entry(map, &priv->freeable_maps, next) {
-		if (!blockable && in_range(map, start, end)) {
+		if (in_range(map, start, end)) {
+			if (blockable)
+				continue;
+			
 			ret = -EAGAIN;
 			goto out_unlock;
 		}
-- 
Michal Hocko
SUSE Labs