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Subject[PATCH] fs/dax: Fix pmd vs pte conflict detection
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Check for NULL entries before checking the entry order, otherwise NULL
is misinterpreted as a present pte conflict. The 'order' check needs to
happen before the locked check as an unlocked entry at the wrong order
must fallback to lookup the correct order.

Reported-by: Jeff Smits <jeff.smits@intel.com>
Reported-by: Doug Nelson <doug.nelson@intel.com>
Cc: <stable@vger.kernel.org>
Fixes: 23c84eb78375 ("dax: Fix missed wakeup with PMD faults")
Cc: Jan Kara <jack@suse.cz>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
fs/dax.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index a71881e77204..08160011d94c 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -221,10 +221,11 @@ static void *get_unlocked_entry(struct xa_state *xas, unsigned int order)

for (;;) {
entry = xas_find_conflict(xas);
+ if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
+ return entry;
if (dax_entry_order(entry) < order)
return XA_RETRY_ENTRY;
- if (!entry || WARN_ON_ONCE(!xa_is_value(entry)) ||
- !dax_is_locked(entry))
+ if (!dax_is_locked(entry))
return entry;

wq = dax_entry_waitqueue(xas, entry, &ewait.key);
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