dax: Fix deadlock in dax_lock_mapping_entry()

When dax_lock_mapping_entry() has to sleep to obtain entry lock, it will
fail to unlock mapping->i_pages spinlock and thus immediately deadlock
against itself when retrying to grab the entry lock again. Fix the
problem by unlocking mapping->i_pages before retrying.

Fixes: c2a7d2a11552 ("filesystem-dax: Introduce dax_lock_mapping_entry()")
Reported-by: Barret Rhoden <brho@google.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/fs/dax.c b/fs/dax.c
index f32d712..e4ef8af 100644 (file)
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -447,6 +447,7 @@ bool dax_lock_mapping_entry(struct page *page)
                        xa_unlock_irq(&mapping->i_pages);
                        break;
                } else if (IS_ERR(entry)) {
+                       xa_unlock_irq(&mapping->i_pages);
                        WARN_ON_ONCE(PTR_ERR(entry) != -EAGAIN);
                        continue;
                }