Mathieu Desnoyers wrote:
> Replace the following fs/Kconfig:FS_DAX dependency:
>
> depends on !(ARM || MIPS || SPARC)
>
> By a runtime check within alloc_dax().
>
> This is done in preparation for its use by each filesystem supporting
> the "dax" mount option to validate whether DAX is indeed supported.
>
> 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 <mathieu.desnoyers@xxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-arch@xxxxxxxxxxxxxxx
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
> Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Russell King <linux@xxxxxxxxxxxxxxx>
> Cc: nvdimm@xxxxxxxxxxxxxxx
> Cc: linux-cxl@xxxxxxxxxxxxxxx
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> Cc: dm-devel@xxxxxxxxxxxxxxx
> ---
> drivers/dax/super.c | 6 ++++++
> fs/Kconfig | 1 -
> 2 files changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index 0da9232ea175..e9f397b8a5a3 100644
> --- a/drivers/dax/super.c
> +++ b/drivers/dax/super.c
> @@ -445,6 +445,12 @@ struct dax_device *alloc_dax(void *private, const struct dax_operations *ops)
> dev_t devt;
> int minor;
>
> + /* Unavailable on architectures with virtually aliased data caches. */
> + if (IS_ENABLED(CONFIG_ARM) ||
> + IS_ENABLED(CONFIG_MIPS) ||
> + IS_ENABLED(CONFIG_SPARC))
> + return NULL;
This function returns ERR_PTR(), not NULL on failure.
...and I notice this mistake is also made in include/linux/dax.h in the
CONFIG_DAX=n case. That function also mentions:
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;
}
...and none of the callers validate the result, but now runtime
validation is necessary. I.e. it is not enough to check
IS_ENABLED(CONFIG_DAX) it also needs to check cpu_dcache_is_aliasing().
With that, there are a few more fixup places needed, pmem_attach_disk(),
dcssblk_add_store(), and virtio_fs_setup_dax().
