[PATCH v2 hmm 09/11] mm/hmm: Poison hmm_range during unregister

[Jason Gunthorpe]

From: Jason Gunthorpe <jgg at mellanox.com>

Trying to misuse a range outside its lifetime is a kernel bug. Use WARN_ON
and poison bytes to detect this condition.

Signed-off-by: Jason Gunthorpe <jgg at mellanox.com>
Reviewed-by: Jérôme Glisse <jglisse at redhat.com>
---
v2
- Keep range start/end valid after unregistration (Jerome)
---
 mm/hmm.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/hmm.c b/mm/hmm.c
index 6802de7080d172..c2fecb3ecb11e1 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -937,7 +937,7 @@ void hmm_range_unregister(struct hmm_range *range)
 	struct hmm *hmm = range->hmm;
 
 	/* Sanity check this really should not happen. */
-	if (hmm == NULL || range->end <= range->start)
+	if (WARN_ON(range->end <= range->start))
 		return;
 
 	mutex_lock(&hmm->lock);
@@ -948,7 +948,10 @@ void hmm_range_unregister(struct hmm_range *range)
 	range->valid = false;
 	mmput(hmm->mm);
 	hmm_put(hmm);
-	range->hmm = NULL;
+
+	/* The range is now invalid, leave it poisoned. */
+	range->valid = false;
+	memset(&range->hmm, POISON_INUSE, sizeof(range->hmm));
 }
 EXPORT_SYMBOL(hmm_range_unregister);
 
-- 
2.21.0