dax: Fix deadlock in dax_lock_mapping_entry()

jankara · djbw · commit f52afc93cd01 · 2018-09-27T10:56:15.000-07:00
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: c2a7d2a ("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
@@ -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;
 		}

Original file line number	Diff line number	Diff line change
`@@ -447,6 +447,7 @@ bool dax_lock_mapping_entry(struct page *page)`
`447`	`447`	`xa_unlock_irq(&mapping->i_pages);`
`448`	`448`	`break;`
`449`	`449`	`} else if (IS_ERR(entry)) {`
	`450`	`+ xa_unlock_irq(&mapping->i_pages);`
`450`	`451`	`WARN_ON_ONCE(PTR_ERR(entry) != -EAGAIN);`
`451`	`452`	`continue;`
`452`	`453`	`}`