linux-kernel - Re: [PATCH v7 1/5] dax/bus.c: replace driver-core lock usage by a local rwsem

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Date: Tue, 12 Mar 2024 13:07:11 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Vishal Verma <vishal.l.verma@...el.com>, Dan Williams
	<dan.j.williams@...el.com>, Dave Jiang <dave.jiang@...el.com>, Andrew Morton
	<akpm@...ux-foundation.org>, Oscar Salvador <osalvador@...e.de>
CC: <linux-kernel@...r.kernel.org>, <nvdimm@...ts.linux.dev>,
	<linux-cxl@...r.kernel.org>, David Hildenbrand <david@...hat.com>, "Dave
 Hansen" <dave.hansen@...ux.intel.com>, Huang Ying <ying.huang@...el.com>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>, Matthew Wilcox
	<willy@...radead.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH v7 1/5] dax/bus.c: replace driver-core lock usage by a
 local rwsem

Vishal Verma wrote:
> The dax driver incorrectly used driver-core device locks to protect
> internal dax region and dax device configuration structures. Replace the
> device lock usage with a local rwsem, one each for dax region
> configuration and dax device configuration. As a result of this
> conversion, no device_lock() usage remains in dax/bus.c.
> 
> Cc: Dan Williams <dan.j.williams@...el.com>
> Reported-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Signed-off-by: Vishal Verma <vishal.l.verma@...el.com>
> ---
>  drivers/dax/bus.c | 220 ++++++++++++++++++++++++++++++++++++++----------------
>  1 file changed, 157 insertions(+), 63 deletions(-)
> 
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index 1ff1ab5fa105..cb148f74ceda 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -12,6 +12,18 @@
>  
>  static DEFINE_MUTEX(dax_bus_lock);
>  
> +/*
> + * All changes to the dax region configuration occur with this lock held
> + * for write.
> + */
> +DECLARE_RWSEM(dax_region_rwsem);
> +
> +/*
> + * All changes to the dax device configuration occur with this lock held
> + * for write.
> + */
> +DECLARE_RWSEM(dax_dev_rwsem);
> +
>  #define DAX_NAME_LEN 30
>  struct dax_id {
>  	struct list_head list;
> @@ -180,7 +192,7 @@ static u64 dev_dax_size(struct dev_dax *dev_dax)
>  	u64 size = 0;
>  	int i;
>  
> -	device_lock_assert(&dev_dax->dev);
> +	WARN_ON_ONCE(!rwsem_is_locked(&dax_dev_rwsem));

Apologies for the late review, but...

All of these WARN_ON_ONCE() usages should be replaced with
lockdep_assert_held() and lockdep_assert_held_write() where appropriate.