Re: [PATCH v5 1/8] dax: alloc_dax() return ERR_PTR(-EOPNOTSUPP) for CONFIG_DAX=n
On 2024-02-13 14:07, Dan Williams wrote:
Lukas Wunner wrote:
On Mon, Feb 12, 2024 at 11:30:54AM -0500, Mathieu Desnoyers wrote:
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.
All the callers of alloc_dax() only check for IS_ERR().
Doesn't this result in a change of behavior in all the callers?
Previously they'd ignore the NULL return value and continue,
now they'll error out.
Given that, seems dangerous to add a Fixes tag with a v4.0 commit
and thus risk regressing all stable kernels.
Oh, good catch, yes that Fixes tag should be:
4e4ced93794a dax: Move mandatory ->zero_page_range() check in alloc_dax()
...as that was the one that updated the alloc_dax() calling convention
without fixing up the CONFIG_DAX=n case.
This is a pre-requisite for restoring DAX operation on ARM32.
I'll change the Fixes tag in this commit to:
Fixes: 4e4ced93794a ("dax: Move mandatory ->zero_page_range() check in
alloc_dax()")
for v6.
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
Re: [PATCH v5 1/8] dax: alloc_dax() return ERR_PTR(-EOPNOTSUPP) for CONFIG_DAX=n
Lukas Wunner wrote: > On Mon, Feb 12, 2024 at 11:30:54AM -0500, Mathieu Desnoyers wrote: > > 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. > > All the callers of alloc_dax() only check for IS_ERR(). > > Doesn't this result in a change of behavior in all the callers? > Previously they'd ignore the NULL return value and continue, > now they'll error out. > > Given that, seems dangerous to add a Fixes tag with a v4.0 commit > and thus risk regressing all stable kernels. Oh, good catch, yes that Fixes tag should be: 4e4ced93794a dax: Move mandatory ->zero_page_range() check in alloc_dax() ...as that was the one that updated the alloc_dax() calling convention without fixing up the CONFIG_DAX=n case. This is a pre-requisite for restoring DAX operation on ARM32.
Re: [PATCH v5 1/8] dax: alloc_dax() return ERR_PTR(-EOPNOTSUPP) for CONFIG_DAX=n
On Mon, Feb 12, 2024 at 11:30:54AM -0500, Mathieu Desnoyers wrote: > 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. All the callers of alloc_dax() only check for IS_ERR(). Doesn't this result in a change of behavior in all the callers? Previously they'd ignore the NULL return value and continue, now they'll error out. Given that, seems dangerous to add a Fixes tag with a v4.0 commit and thus risk regressing all stable kernels. Thanks, Lukas
[PATCH v5 1/8] 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.
Fixes: d92576f1167c ("dax: does not work correctly with virtual aliasing
caches")
Signed-off-by: Mathieu Desnoyers
Reviewed-by: Dan Williams
Cc: Andrew Morton
Cc: Linus Torvalds
Cc: Dan Williams
Cc: Vishal Verma
Cc: Dave Jiang
Cc: Matthew Wilcox
Cc: Arnd Bergmann
Cc: Russell King
Cc: linux-a...@vger.kernel.org
Cc: linux-...@vger.kernel.org
Cc: linux-fsde...@vger.kernel.org
Cc: linux...@kvack.org
Cc: linux-...@vger.kernel.org
Cc: dm-devel@lists.linux.dev
Cc: nvd...@lists.linux.dev
---
drivers/dax/super.c | 5 +
include/linux/dax.h | 6 +-
2 files changed, 6 insertions(+), 5 deletions(-)
diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 0da9232ea175..205b888d45bf 100644
--- 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 b463502b16e1..df2d52b8a245 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -86,11 +86,7 @@ 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)
{
--
2.39.2
