Re: [PATCH v2] dax: fix for do not print error message for non-persistent memory block device

[Mike Snitzer <snitzer@redhat.com>]

On Thu, Sep 03 2020 at 11:28am -0400,
Coly Li <colyli@suse.de> 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)) {

Don't think I've ever seen a one-liner fix document the diff in its
patch header.  Really no need for that.

> Fixes: c2affe920b0e ("dax: do not print error message for non-persistent memory block device")
> Signed-off-by: Coly Li <colyli@suse.de>
> Reviewed-and-Tested-by: Adrian Huang <ahuang12@lenovo.com>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Cc: Jan Kara <jack@suse.com>
> Cc: Mike Snitzer <snitzer@redhat.com>
> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
> Cc: Vishal Verma <vishal.l.verma@intel.com>

Thanks for fixing this,

Reviewed-by: Mike Snitzer <snitzer@redhat.com>


> ---
> Changelog:
> v2: add Reviewed-and-Tested-by from Adrian Huang.
> v1: initial version.
> 
>  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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