On Fri, 2015-01-30 at 10:00 +0100, Geert Uytterhoeven wrote: > Hi Michael, > > On Fri, Jan 30, 2015 at 5:09 AM, Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote: > > On Wed, 2015-14-01 at 13:51:57 UTC, Geert Uytterhoeven wrote: > >> of_find_node_by_name() calls of_node_put() on its "from" parameter, > >> which must not be done on "master", as it's still in use, and will be > >> released manually later. This may cause a zero kref refcount. > >> Use of_get_child_by_name() instead to fix this. > > > > But of_find_node_by_name() searches *all* nodes, not just the children of the > > parameter. > > That's correct. However, I guess the second mac-io will just be a direct child. Yeah OK, I don't have a system or an example device tree to check. > > So this is a logic change AFAICS, and I have no idea what machines we'd need to > > test on to check it. > > Originally it comes from arch/ppc/platforms/pmac_pic.c, added in 2002 in > full-history-linux commit 5ea3254844ae344a > ("Import arch/ppc and include/asm-ppc changes from linuxppc_2_5 tree"). > > I've also checked my linuxppc mail archives from 1997-2002, but couldn't find > the actual patch and a description. > > So I don't know on which machines it's needed. Yep. Ben or Paul might know, but even then their memory may not be perfect :) > > So I think an of_node_get(master) would be safer and also fix the refcounting. > > If no one can confirm the above, that may indeed be the best solution. I think so. Given how few of these machines are around it's easy to break them with an inadvertent change like this, so I think it's better to be safe. Wanna send a patch for that? cheers -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html