of: fix phandle cache creation for DTs with no phandles

commit e54192b48da75f025ae4b277925eaf6aca1d13bd upstream.

With commit 0b3ce78e90fc ("of: cache phandle nodes to reduce cost of
of_find_node_by_phandle()"), a G3 PowerMac fails to boot. The root cause
is the DT for this system has no phandle properties when booted with
BootX. of_populate_phandle_cache() does not handle the case of no
phandles correctly. The problem is roundup_pow_of_two() for 0 is
undefined. The implementation subtracts 1 underflowing and then things
are in the weeds.

Fixes: 0b3ce78e90fc ("of: cache phandle nodes to reduce cost of of_find_node_by_phandle()")
Cc: stable@vger.kernel.org # 4.17+
Reported-by: Finn Thain <fthain@telegraphics.com.au>
Tested-by: Stan Johnson <userm57@yahoo.com>
Reviewed-by: Frank Rowand <frank.rowand@sony.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/of/base.c b/drivers/of/base.c
index 466e3c8582f0fd62628b90872b2046971e064776..71d10e392736a3bbf5f8547acce4db13b796a042 100644 (file)
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -118,6 +118,9 @@ void of_populate_phandle_cache(void)
                if (np->phandle && np->phandle != OF_PHANDLE_ILLEGAL)
                        phandles++;
 
+       if (!phandles)
+               goto out;
+
        cache_entries = roundup_pow_of_two(phandles);
        phandle_cache_mask = cache_entries - 1;