From b0d65a8cbcb097d2110885c3660add97b0125867 Mon Sep 17 00:00:00 2001
From: Oliver O'Halloran <oohall@gmail.com>
Date: Fri, 7 Dec 2018 02:17:12 +1100
Subject: [PATCH] powerpc/papr_scm: Fix DIMM device registration race

References: FATE#326628, bsc#1113295, git-fixes)
Patch-mainline: v4.20-rc7
Git-commit: b0d65a8cbcb097d2110885c3660add97b0125867

When a new nvdimm device is registered with libnvdimm via
nvdimm_create() it is added as a device on the nvdimm bus. The probe
function for the DIMM driver is potentially quite slow so actually
registering and probing the device is done in an async domain rather
than immediately after device creation. This can result in a race where
the region device (created 2nd) is probed first and fails to activate at
boot.

To fix this we use the same approach as the ACPI/NFIT driver which is to
check that all the DIMM devices registered successfully. LibNVDIMM
provides the nvdimm_bus_count_dimms() function which synchronises with
the async domain and verifies that the dimm was successfully registered
with the bus.

If either of these does not occur then we bail.

Fixes: b5beae5e224f ("powerpc/pseries: Add driver for PAPR SCM regions")
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
 arch/powerpc/platforms/pseries/papr_scm.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
index 8b5153c55da6..7dc6a751cb4c 100644
--- a/arch/powerpc/platforms/pseries/papr_scm.c
+++ b/arch/powerpc/platforms/pseries/papr_scm.c
@@ -223,6 +223,9 @@ static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
 		goto err;
 	}
 
+	if (nvdimm_bus_check_dimm_count(p->bus, 1))
+		goto err;
+
 	/* now add the region */
 
 	memset(&mapping, 0, sizeof(mapping));
-- 
2.19.2