linux-kernel - Re: [PATCH v3 8/8] cxl: Convert to ACQUIRE() for conditional rwsem locking

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Message-ID: <20250715172035.00007f96@huawei.com>
Date: Tue, 15 Jul 2025 17:20:35 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Dan Williams <dan.j.williams@...el.com>
CC: <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>, David Lechner
	<dlechner@...libre.com>, Peter Zijlstra <peterz@...radead.org>, "Linus
 Torvalds" <torvalds@...ux-foundation.org>, Ingo Molnar <mingo@...nel.org>,
	"Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>, "Davidlohr
 Bueso" <dave@...olabs.net>, Dave Jiang <dave.jiang@...el.com>, "Alison
 Schofield" <alison.schofield@...el.com>, Vishal Verma
	<vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>, Shiju Jose
	<shiju.jose@...wei.com>
Subject: Re: [PATCH v3 8/8] cxl: Convert to ACQUIRE() for conditional rwsem
 locking

On Fri, 11 Jul 2025 16:49:32 -0700
Dan Williams <dan.j.williams@...el.com> wrote:

> Use ACQUIRE() to cleanup conditional locking paths in the CXL driver
> The ACQUIRE() macro and its associated ACQUIRE_ERR() helpers, like
> scoped_cond_guard(), arrange for scoped-based conditional locking. Unlike
> scoped_cond_guard(), these macros arrange for an ERR_PTR() to be retrieved
> representing the state of the conditional lock.
> 
> The goal of this conversion is to complete the removal of all explicit
> unlock calls in the subsystem. I.e. the methods to acquire a lock are
> solely via guard(), scoped_guard() (for limited cases), or ACQUIRE(). All
> unlock is implicit / scope-based. In order to make sure all lock sites are
> converted, the existing rwsem's are consolidated and renamed in 'struct
> cxl_rwsem'. While that makes the patch noisier it gives a clean cut-off
> between old-world (explicit unlock allowed), and new world (explicit unlock
> deleted).
> 
> Cc: David Lechner <dlechner@...libre.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: "Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>
> Cc: Davidlohr Bueso <dave@...olabs.net>
> Cc: Jonathan Cameron <jonathan.cameron@...wei.com>
> Cc: Dave Jiang <dave.jiang@...el.com>
> Cc: Alison Schofield <alison.schofield@...el.com>
> Cc: Vishal Verma <vishal.l.verma@...el.com>
> Cc: Ira Weiny <ira.weiny@...el.com>
> Cc: Shiju Jose <shiju.jose@...wei.com>
> Acked-by: "Peter Zijlstra (Intel)" <peterz@...radead.org>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>

Two trivial comments inline. 

Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>

> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 4314aaed8ad8..ad60c93be803 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c

>  static int attach_target(struct cxl_region *cxlr,
>  			 struct cxl_endpoint_decoder *cxled, int pos,
>  			 unsigned int state)
>  {
> -	int rc = 0;
> -
> -	if (state == TASK_INTERRUPTIBLE)
> -		rc = down_write_killable(&cxl_region_rwsem);
> -	else
> -		down_write(&cxl_region_rwsem);
> -	if (rc)
> -		return rc;
> -
> -	down_read(&cxl_dpa_rwsem);
> -	rc = cxl_region_attach(cxlr, cxled, pos);
> -	up_read(&cxl_dpa_rwsem);
> -	up_write(&cxl_region_rwsem);
> +	int rc = __attach_target(cxlr, cxled, pos, state);
>  

... (start of block for next comment)

> -	if (rc)
> -		dev_warn(cxled->cxld.dev.parent,
> -			"failed to attach %s to %s: %d\n",
> -			dev_name(&cxled->cxld.dev), dev_name(&cxlr->dev), rc);
> +	if (rc == 0)
> +		return 0;
>  
> +	dev_warn(cxled->cxld.dev.parent, "failed to attach %s to %s: %d\n",
> +		 dev_name(&cxled->cxld.dev), dev_name(&cxlr->dev), rc);

I'm not seeing a reason for this change.  I prefer the original
with the error path as the out of line case.


>  	return rc;
>  }


> @@ -3592,30 +3552,23 @@ static int cxl_region_can_probe(struct cxl_region *cxlr)
...
  
>  	if (test_bit(CXL_REGION_F_NEEDS_RESET, &cxlr->flags)) {
>  		dev_err(&cxlr->dev,
>  			"failed to activate, re-commit region and retry\n");
> -		rc = -ENXIO;
> -		goto out;
> +		return -ENXIO;

		return dev_err_probe(&cxlr->dev, -ENXIO,
				     "failed to activate, re-commit region and retry\n");

perhaps. I always like the cleanup.h stuff enabling this as it improves the patch
line count no end ;)


>  	}
>  
> -out:
> -	up_read(&cxl_region_rwsem);
> -
> -	if (rc)
> -		return rc;
>  	return 0;
>  }