4.16 kernel: atomic_dec_and_test() changed

[tonyhutter]

I hit these errors building against the 4.16 nightly kernel packages (http://kernel.ubuntu.com/~kernel-ppa/mainline/daily/current/):

  CC [M]  /home/hutter/zfs/module/zcommon/zpool_prop.o
  CC [M]  /home/hutter/zfs/module/lua/lfunc.o
In file included from /home/hutter/zfs/include/sys/zpl.h:37:0,
                 from /home/hutter/zfs/module/zfs/arc.c:298:
/home/hutter/zfs/include/linux/vfs_compat.h: In function ‘zpl_posix_acl_release’:
/home/hutter/zfs/include/linux/vfs_compat.h:292:26: error: passing argument 1 of ‘atomic_dec_and_test’ from incompatible pointer type [-Werror=incompatible-pointer-types]
  if (atomic_dec_and_test(&acl->a_refcount))
                          ^
In file included from ./arch/x86/include/asm/msr.h:67:0,
                 from ./arch/x86/include/asm/processor.h:21,
                 from ./arch/x86/include/asm/cpufeature.h:5,
                 from ./arch/x86/include/asm/thread_info.h:53,
                 from ./include/linux/thread_info.h:38,
                 from ./arch/x86/include/asm/preempt.h:7,
                 from ./include/linux/preempt.h:81,
                 from ./include/linux/spinlock.h:51,
                 from ./include/linux/seqlock.h:36,
                 from ./include/linux/time.h:6,
                 from ./include/linux/stat.h:19,
                 from ./include/linux/module.h:10,
                 from /home/hutter/zfs/../spl/include/sys/sysmacros.h:28,
                 from /home/hutter/zfs/../spl/include/sys/types.h:29,
                 from /home/hutter/zfs/include/sys/avl.h:42,
                 from /home/hutter/zfs/include/sys/spa.h:35,
                 from /home/hutter/zfs/module/zfs/arc.c:278:
./arch/x86/include/asm/atomic.h:116:29: note: expected ‘atomic_t * {aka struct <anonymous> *}’ but argument is of type ‘refcount_t * {aka struct refcount_struct *}’
 static __always_inline bool atomic_dec_and_test(atomic_t *v)
                             ^~~~~~~~~~~~~~~~~~~
  CC [M]  /home/hutter/zfs/module/icp/core/kcf_prov_tabs.o
  CC [M]  /home/hutter/zfs/module/zcommon/zprop_common.o

System information

Type	Version/Name
Distribution Name	Ubuntu
Distribution Version	17.10
Linux Kernel	4.16.0-999-generic
Architecture	x86-64
ZFS Version	master e921f65
SPL Version	master 48ef8ba

[tonyhutter]

This seems to fix it:

diff --git a/include/linux/vfs_compat.h b/include/linux/vfs_compat.h
index 7fcf3c055..f20905b34 100644
--- a/include/linux/vfs_compat.h
+++ b/include/linux/vfs_compat.h
@@ -289,7 +289,7 @@ zpl_posix_acl_release(struct posix_acl *acl)
        if ((acl == NULL) || (acl == ACL_NOT_CACHED))
                return;
 
-       if (atomic_dec_and_test(&acl->a_refcount))
+       if (refcount_dec_and_test(&acl->a_refcount))
                zpl_posix_acl_release_impl(acl);
 }
 #endif /* HAVE_POSIX_ACL_RELEASE */

https://www.redhat.com/archives/linux-audit/2017-July/msg00060.html

I'll put together a PR

[behlendorf]

It looks like we're going to need a little more compatibility code for this.

[tonyhutter]

@behlendorf yea, I'll do the normal autoconf tests for it.