On Thu, Sep 03, 2020 at 07:55:49PM +0800, Coly Li wrote:
> When calling __generic_fsdax_supported(), a dax-unsupported device may
> not have dax_dev as NULL, e.g. the dax related code block is not enabled
> by Kconfig.
>
> Therefore in __generic_fsdax_supported(), to check whether a device
> supports DAX or not, the following order should be performed,
> - If dax_dev pointer is NULL, it means the device driver explicitly
> announce it doesn't support DAX. Then it is OK to directly return
> false from __generic_fsdax_supported().
> - If dax_dev pointer is NOT NULL, it might be because the driver doesn't
> support DAX and not explicitly initialize related data structure. Then
> bdev_dax_supported() should be called for further check.
>
> IMHO if device driver desn't explicitly set its dax_dev pointer to NULL,
> this is not a bug. Calling bdev_dax_supported() makes sure they can be
> recognized as dax-unsupported eventually.
>
> This patch does the following change for the above purpose,
> - if (!dax_dev && !bdev_dax_supported(bdev, blocksize)) {
> + if (!dax_dev || !bdev_dax_supported(bdev, blocksize)) {
>
>
> Fixes: c2affe920b0e ("dax: do not print error message for non-persistent memory block device")
> Signed-off-by: Coly Li <colyli@xxxxxxx>
I hate to do this because I realize this is a bug which people really need
fixed.
However, shouldn't we also check (!dax_dev || !bdev_dax_supported()) as the
_first_ check in __generic_fsdax_supported()?
It seems like the other pr_info's could also be called when DAX is not
supported and we probably don't want them to be?
Perhaps that should be a follow on patch though. So...
As a direct fix to c2affe920b0e
Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> Cc: Adrian Huang <ahuang12@xxxxxxxxxx>
> Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxxx>
> Cc: Mike Snitzer <snitzer@xxxxxxxxxx>
> Cc: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx>
> Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
> ---
> drivers/dax/super.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index 32642634c1bb..e5767c83ea23 100644
> --- a/drivers/dax/super.c
> +++ b/drivers/dax/super.c
> @@ -100,7 +100,7 @@ bool __generic_fsdax_supported(struct dax_device *dax_dev,
> return false;
> }
>
> - if (!dax_dev && !bdev_dax_supported(bdev, blocksize)) {
> + if (!dax_dev || !bdev_dax_supported(bdev, blocksize)) {
> pr_debug("%s: error: dax unsupported by block device\n",
> bdevname(bdev, buf));
> return false;
> --
> 2.26.2
>
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