linux-kernel - [PATCH 4.19 28/30] powerpc/pseries: Fix regression while building external modules

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Date:   Mon,  2 Aug 2021 15:45:06 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, marc.c.dionne@...il.com,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: [PATCH 4.19 28/30] powerpc/pseries: Fix regression while building external modules

From: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>

commit 333cf507465fbebb3727f5b53e77538467df312a upstream.

With commit c9f3401313a5 ("powerpc: Always enable queued spinlocks for
64s, disable for others") CONFIG_PPC_QUEUED_SPINLOCKS is always
enabled on ppc64le, external modules that use spinlock APIs are
failing.

  ERROR: modpost: GPL-incompatible module XXX.ko uses GPL-only symbol 'shared_processor'

Before the above commit, modules were able to build without any
issues. Also this problem is not seen on other architectures. This
problem can be workaround if CONFIG_UNINLINE_SPIN_UNLOCK is enabled in
the config. However CONFIG_UNINLINE_SPIN_UNLOCK is not enabled by
default and only enabled in certain conditions like
CONFIG_DEBUG_SPINLOCKS is set in the kernel config.

  #include <linux/module.h>
  spinlock_t spLock;

  static int __init spinlock_test_init(void)
  {
          spin_lock_init(&spLock);
          spin_lock(&spLock);
          spin_unlock(&spLock);
          return 0;
  }

  static void __exit spinlock_test_exit(void)
  {
  	printk("spinlock_test unloaded\n");
  }
  module_init(spinlock_test_init);
  module_exit(spinlock_test_exit);

  MODULE_DESCRIPTION ("spinlock_test");
  MODULE_LICENSE ("non-GPL");
  MODULE_AUTHOR ("Srikar Dronamraju");

Given that spin locks are one of the basic facilities for module code,
this effectively makes it impossible to build/load almost any non GPL
modules on ppc64le.

This was first reported at https://github.com/openzfs/zfs/issues/11172

Currently shared_processor is exported as GPL only symbol.
Fix this for parity with other architectures by exposing
shared_processor to non-GPL modules too.

Fixes: 14c73bd344da ("powerpc/vcpu: Assume dedicated processors as non-preempt")
Cc: stable@...r.kernel.org # v5.5+
Reported-by: marc.c.dionne@...il.com
Signed-off-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Link: https://lore.kernel.org/r/20210729060449.292780-1-srikar@linux.vnet.ibm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/powerpc/platforms/pseries/setup.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -76,7 +76,7 @@
 #include "../../../../drivers/pci/pci.h"

 DEFINE_STATIC_KEY_FALSE(shared_processor);
-EXPORT_SYMBOL_GPL(shared_processor);
+EXPORT_SYMBOL(shared_processor);

 int CMO_PrPSP = -1;
 int CMO_SecPSP = -1;