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:

quoted

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