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

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Message-ID: <691f8616-f39f-449c-bb6e-541c0dcfa974@intel.com>
Date: Tue, 15 Jul 2025 10:38:00 -0700
From: Dave Jiang <dave.jiang@...el.com>
To: dan.j.williams@...el.com, Jonathan Cameron <Jonathan.Cameron@...wei.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>,
 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 7/15/25 10:13 AM, dan.j.williams@...el.com wrote:
> Jonathan Cameron wrote:
>> 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.
> 
> I prefer the out-dent of the message. I'll let Dave tie-break.

I'm leaning towards leaving it alone if there's no functional change. If there's a v4 then revert the changes, otherwise I guess just let it be.

DJ

> 
>>>  	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 ;)
> 
> I think that looks good, but perhaps as a follow-on cleanup?