Users reported a v5.3 performance regression and inability to establish huge page mappings. A revised version of the ndctl "dax.sh" huge page unit test identifies commit 23c84eb78375 "dax: Fix missed wakeup with PMD faults" as the source.
Update get_unlocked_entry() to 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") Reviewed-by: Jan Kara jack@suse.cz Cc: Jeff Moyer jmoyer@redhat.com Cc: Matthew Wilcox (Oracle) willy@infradead.org Signed-off-by: Dan Williams dan.j.williams@intel.com --- Changes in v2: - Update the changelog to reflect the user visible effects of the bug (Jeff)
fs/dax.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c index 6bf81f931de3..2cc43cd914eb 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -220,10 +220,11 @@ 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);