dax: alloc_dax() return ERR_PTR(-EOPNOTSUPP) for CONFIG_DAX=n

Change the return value from NULL to PTR_ERR(-EOPNOTSUPP) for
CONFIG_DAX=n to be consistent with the fact that CONFIG_DAX=y
never returns NULL.

This is done in preparation for using cpu_dcache_is_aliasing() in a
following change which will properly support architectures which detect
data cache aliasing at runtime.

Link: https://lkml.kernel.org/r/20240215144633.96437-3-mathieu.desnoyers@efficios.com
Fixes: 4e4ced93794a ("dax: Move mandatory ->zero_page_range() check in alloc_dax()")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Alasdair Kergon <agk@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: kernel test robot <lkp@intel.com>
Cc: Michael Sclafani <dm-devel@lists.linux.dev>
Cc: Mike Snitzer <snitzer@kernel.org>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index f4b635526345adcffb2bf3031c35a464599fef1d..97ef2a9d878d12e8f1ea9e61d629e1af0b7d3e0c 100644 (file)
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -319,6 +319,11 @@ EXPORT_SYMBOL_GPL(dax_alive);
  * that any fault handlers or operations that might have seen
  * dax_alive(), have completed.  Any operations that start after
  * synchronize_srcu() has run will abort upon seeing !dax_alive().
+ *
+ * Note, because alloc_dax() returns an ERR_PTR() on error, callers
+ * typically store its result into a local variable in order to check
+ * the result. Therefore, care must be taken to populate the struct
+ * device dax_dev field make sure the dax_dev is not leaked.
  */
 void kill_dax(struct dax_device *dax_dev)
 {

diff --git a/include/linux/dax.h b/include/linux/dax.h
index e3ffe7c7f01dacd0e5f354bcde4a9d9c966e9fb6..9d3e3327af4c055f0a6d7a907f2e1d68a345814d 100644 (file)
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -88,11 +88,7 @@ static inline void *dax_holder(struct dax_device *dax_dev)
 static inline struct dax_device *alloc_dax(void *private,
                const struct dax_operations *ops)
 {
-       /*
-        * Callers should check IS_ENABLED(CONFIG_DAX) to know if this
-        * NULL is an error or expected.
-        */
-       return NULL;
+       return ERR_PTR(-EOPNOTSUPP);
 }
 static inline void put_dax(struct dax_device *dax_dev)
 {