From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.10]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 353E234DB48; Fri, 20 Feb 2026 15:55:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.10 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771602907; cv=none; b=KM7l5IupFxMsAJ8h1/84OqQgHFfH1iIzU1S5WKQqyD5KvJAgtKJPIytgf6DOmGh2pDJO1WOw3ab7GzZ39YhfQR/FlFhGlGCVEQ+Bm/4kuIuTjhugZxI1nTSxI7h4FoTCLHx3Tfro5D5AWjqze/7YHxo6l3SouevqwEeQ7xN4yoo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771602907; c=relaxed/simple; bh=TNAwc4bN+gdZnNY9DlBqYik5zqX6LZBfVTFFf/fjt+I=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ajT7cDHfIvmqQwRdgBDFcj2o5hpYnvWfklnGRlqDc2Rf2CwNmGJib0MZfgf6aaX5pUfTqHsDmQHnhJbEN1QijQUQ5fFXla5tPTvYrxIEwKFrcLlcZA8Nq+JFHMbkAWF8rumQWOwbLUUkQ4S4MBkuRNzUhl4GoGYaQZsqUAxtHUo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=fqrrNLFo; arc=none smtp.client-ip=192.198.163.10 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="fqrrNLFo" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1771602906; x=1803138906; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=TNAwc4bN+gdZnNY9DlBqYik5zqX6LZBfVTFFf/fjt+I=; b=fqrrNLFoewZcbcvOgj5jpvTsGEeBE9UW91a1+d1lrDR7a1B6vbTV5GNH +NFMjIn2TEhizghIaY+govh04h5PsWE1d6RmlklcT2wT2bA7M5eYz6dRP 2UST3+Lp4p3+mxq92Dgh0RRC3JItFe6Yyx1LJHZ5RoM3DCfh6lt+dxUvD EK9TlB7mn0lni/z/uAt0QKB/DG6/GBsXHjv7uAEA4QtNA6VLAmYIshEqS UUVKPc4VXwkkWxwnHvthPSyP667ftPc2EbJQ68JxA2MLwpOqqm4Dc39Rf G94aMDxemgBMGRJuj37/+vBiYngSY0QoRW0w62kpqUWeXMlTZFg8Cuf2n A==; X-CSE-ConnectionGUID: ig7gjOZqTd6JPNxZYYSl0g== X-CSE-MsgGUID: 4PDTh675Tti2HAHCiayX3w== X-IronPort-AV: E=McAfee;i="6800,10657,11707"; a="84057103" X-IronPort-AV: E=Sophos;i="6.21,302,1763452800"; d="scan'208";a="84057103" Received: from fmviesa010.fm.intel.com ([10.60.135.150]) by fmvoesa104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Feb 2026 07:55:05 -0800 X-CSE-ConnectionGUID: Z22wXQvOSY6+DvjpXIPJRA== X-CSE-MsgGUID: DyzgI+7cRBmJGEbceuo8xA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.21,302,1763452800"; d="scan'208";a="213432501" Received: from gabaabhi-mobl2.amr.corp.intel.com (HELO [10.125.110.83]) ([10.125.110.83]) by fmviesa010-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Feb 2026 07:55:03 -0800 Message-ID: <00813ddb-e737-4b61-9ebd-07ca2d02fd6c@intel.com> Date: Fri, 20 Feb 2026 08:55:02 -0700 Precedence: bulk X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 7/9] dax: Add deferred-work helpers for dax_hmem and dax_cxl coordination To: "Koralahalli Channabasappa, Smita" , Smita Koralahalli , linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org, nvdimm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-pm@vger.kernel.org Cc: Ard Biesheuvel , Alison Schofield , Vishal Verma , Ira Weiny , Dan Williams , Jonathan Cameron , Yazen Ghannam , Davidlohr Bueso , Matthew Wilcox , Jan Kara , "Rafael J . Wysocki" , Len Brown , Pavel Machek , Li Ming , Jeff Johnson , Ying Huang , Yao Xingtao , Peter Zijlstra , Greg Kroah-Hartman , Nathan Fontenot , Terry Bowman , Robert Richter , Benjamin Cheatham , Zhijian Li , Borislav Petkov , Tomasz Wolski References: <20260210064501.157591-1-Smita.KoralahalliChannabasappa@amd.com> <20260210064501.157591-8-Smita.KoralahalliChannabasappa@amd.com> <0c464a2c-3722-45e5-9023-5a2fce8aa096@intel.com> <9b54bd0a-86dd-493b-92be-680c99b23479@amd.com> Content-Language: en-US From: Dave Jiang In-Reply-To: <9b54bd0a-86dd-493b-92be-680c99b23479@amd.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 2/19/26 5:02 PM, Koralahalli Channabasappa, Smita wrote: > Hi Dave, > > On 2/18/2026 9:52 AM, Dave Jiang wrote: >> >> >> On 2/9/26 11:44 PM, Smita Koralahalli wrote: >>> Add helpers to register, queue and flush the deferred work. >>> >>> These helpers allow dax_hmem to execute ownership resolution outside the >>> probe context before dax_cxl binds. >>> >>> Signed-off-by: Smita Koralahalli >>> --- >>>   drivers/dax/bus.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++ >>>   drivers/dax/bus.h |  7 ++++++ >>>   2 files changed, 65 insertions(+) >>> >>> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c >>> index 5f387feb95f0..92b88952ede1 100644 >>> --- a/drivers/dax/bus.c >>> +++ b/drivers/dax/bus.c >>> @@ -25,6 +25,64 @@ DECLARE_RWSEM(dax_region_rwsem); >>>    */ >>>   DECLARE_RWSEM(dax_dev_rwsem); >>>   +static DEFINE_MUTEX(dax_hmem_lock); >>> +static dax_hmem_deferred_fn hmem_deferred_fn; >>> +static void *dax_hmem_data; >>> + >>> +static void hmem_deferred_work(struct work_struct *work) >>> +{ >>> +    dax_hmem_deferred_fn fn; >>> +    void *data; >>> + >>> +    scoped_guard(mutex, &dax_hmem_lock) { >>> +        fn = hmem_deferred_fn; >>> +        data = dax_hmem_data; >>> +    } >>> + >>> +    if (fn) >>> +        fn(data); >>> +} >> >> Instead of having a global lock and dealing with all the global variables, why not just do this with the typical work_struct usage pattern and allocate a work item when queuing work? >> >> DJ > > Thanks for the feedback. > > Just to clarify, are you hinting towards a statically allocated struct > with an embedded work_struct, something like below? Rather than the typical kmalloc + container_of pattern? > > +struct dax_hmem_deferred_ctx { > +    struct work_struct work; > +    dax_hmem_deferred_fn fn; > +    void *data; > +}; > > +static struct dax_hmem_deferred_ctx dax_hmem_ctx; > > +int dax_hmem_register_work(dax_hmem_deferred_fn fn, void *data) > +{ > +    if (dax_hmem_ctx.fn) > +        return -EINVAL; > > +    INIT_WORK(&dax_hmem_ctx.work, hmem_deferred_work); > .. > > My understanding is that Dan wanted this to remain a singleton deferred work item queued once and flushed from dax_cxl. I think with kmalloc + container_of approach, every call would allocate and queue a new independent work item.. > > Regarding the mutex: looking at it again, it may not be necessary I think. If we can rely on the call ordering (register_work() before queue_work()), and if flush_work() in kill_defer_work() ensures the work has fully completed before unregister_work() NULLs the pointers, then the static struct above would be sufficient without additional locking. If I'm missing a scenario or race here, please correct me. Ok I missed the history on the single issue work item. Yes what you proposed above should work if it's single issue. and if we are only sending 1 item, a statically declared work context should be sufficient I think. DJ > > Thanks, > Smita > >> >>> + >>> +static DECLARE_WORK(dax_hmem_work, hmem_deferred_work); >>> + >>> +int dax_hmem_register_work(dax_hmem_deferred_fn fn, void *data) >>> +{ >>> +    guard(mutex)(&dax_hmem_lock); >>> + >>> +    if (hmem_deferred_fn) >>> +        return -EINVAL; >>> + >>> +    hmem_deferred_fn = fn; >>> +    dax_hmem_data = data; >>> +    return 0; >>> +} >>> +EXPORT_SYMBOL_GPL(dax_hmem_register_work); >>> + >>> +int dax_hmem_unregister_work(dax_hmem_deferred_fn fn, void *data) >>> +{ >>> +    guard(mutex)(&dax_hmem_lock); >>> + >>> +    if (hmem_deferred_fn != fn || dax_hmem_data != data) >>> +        return -EINVAL; >>> + >>> +    hmem_deferred_fn = NULL; >>> +    dax_hmem_data = NULL; >>> +    return 0; >>> +} >>> +EXPORT_SYMBOL_GPL(dax_hmem_unregister_work); >>> + >>> +void dax_hmem_queue_work(void) >>> +{ >>> +    queue_work(system_long_wq, &dax_hmem_work); >>> +} >>> +EXPORT_SYMBOL_GPL(dax_hmem_queue_work); >>> + >>> +void dax_hmem_flush_work(void) >>> +{ >>> +    flush_work(&dax_hmem_work); >>> +} >>> +EXPORT_SYMBOL_GPL(dax_hmem_flush_work); >>> + >>>   #define DAX_NAME_LEN 30 >>>   struct dax_id { >>>       struct list_head list; >>> diff --git a/drivers/dax/bus.h b/drivers/dax/bus.h >>> index cbbf64443098..b58a88e8089c 100644 >>> --- a/drivers/dax/bus.h >>> +++ b/drivers/dax/bus.h >>> @@ -41,6 +41,13 @@ struct dax_device_driver { >>>       void (*remove)(struct dev_dax *dev); >>>   }; >>>   +typedef void (*dax_hmem_deferred_fn)(void *data); >>> + >>> +int dax_hmem_register_work(dax_hmem_deferred_fn fn, void *data); >>> +int dax_hmem_unregister_work(dax_hmem_deferred_fn fn, void *data); >>> +void dax_hmem_queue_work(void); >>> +void dax_hmem_flush_work(void); >>> + >>>   int __dax_driver_register(struct dax_device_driver *dax_drv, >>>           struct module *module, const char *mod_name); >>>   #define dax_driver_register(driver) \ >> >