linux-kernel - Re: [PATCH] [HACK] drop zen5

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Message-ID: <aFo68StiDKzLjNdS@rric.localdomain>
Date: Tue, 24 Jun 2025 07:43:13 +0200
From: Robert Richter <rrichter@....com>
To: Joshua Hahn <joshua.hahnjy@...il.com>
Cc: Gregory Price <gourry@...rry.net>,
	Alison Schofield <alison.schofield@...el.com>,
	Vishal Verma <vishal.l.verma@...el.com>,
	Ira Weiny <ira.weiny@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Terry Bowman <terry.bowman@....com>, linux-cxl@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>
Subject: Re: [PATCH] [HACK] drop zen5_init checks due to segfault

On 17.06.25 13:33:18, Joshua Hahn wrote:
> I was hoping for some help in understanding your explanation here -- I don't
> think I can see where the dependency appears. (In particular, I'm having
> trouble understanding where the efi_rts_wq dependnecy matters during the
> cxl_zen5_init function). 

Here a temporary patch with an explanation in the description:


>From a540b814d48574b67a9aaa97a5d7536c61d4deda Mon Sep 17 00:00:00 2001
From: Robert Richter <rrichter@....com>
Date: Tue, 13 May 2025 15:02:16 +0200
Subject: [PATCH] cxl/acpi: Prepare use of EFI runtime services

In order to use EFI runtime services, esp. ACPI PRM which uses the
efi_rts_wq workqueue, initialize EFI before CXL ACPI.

There is a subsys_initcall order dependency if driver is builtin:

 subsys_initcall(cxl_acpi_init);
 subsys_initcall(efisubsys_init);

Prevent the efi_rts_wq workqueue being used by cxl_acpi_init() before
its allocation. Use subsys_initcall_sync(cxl_acpi_init) to always run
efisubsys_init() first.

Reported-by: Gregory Price <gourry@...rry.net>
Signed-off-by: Robert Richter <rrichter@....com>
---
 drivers/cxl/acpi.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
index a1a99ec3f12c..af750a8bd373 100644
--- a/drivers/cxl/acpi.c
+++ b/drivers/cxl/acpi.c
@@ -932,8 +932,12 @@ static void __exit cxl_acpi_exit(void)
 	cxl_bus_drain();
 }
 
-/* load before dax_hmem sees 'Soft Reserved' CXL ranges */
-subsys_initcall(cxl_acpi_init);
+/*
+ * Load before dax_hmem sees 'Soft Reserved' CXL ranges. Use
+ * subsys_initcall_sync() since there is an order dependency with
+ * subsys_initcall(efisubsys_init), which must run first.
+ */
+subsys_initcall_sync(cxl_acpi_init);
 
 /*
  * Arrange for host-bridge ports to be active synchronous with
-- 
2.39.5