of: make of_update_property() usable earlier in the boot process

Commit 75b57ecf9d ('of: Make device
nodes kobjects so they show up in sysfs') has turned Device Tree nodes
in kobjects and added a sysfs based representation for Device Tree
nodes. Since the sysfs logic is only available after the execution of
a core_initcall(), the patch took precautions in of_add_property() and
of_remove_property() to not do any sysfs related manipulation early in
the boot process.

However, it forgot to do the same for of_update_property(), which if
used early in the boot process (before core_initcalls have been
called), tries to call sysfs_remove_bin_file(), and crashes:

------------[ cut here ]------------
WARNING: CPU: 0 PID: 0 at /home/thomas/projets/linux-2.6/fs/kernfs/dir.c:1216 kernfs_remove_by_name_ns+0x80/0x88()
kernfs: can not remove '(null)', no directory
Modules linked in:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.15.0-rc1-00127-g1d7e7b2-dirty #423
[<c0014910>] (unwind_backtrace) from [<c00110ec>] (show_stack+0x10/0x14)
[<c00110ec>] (show_stack) from [<c04c84b8>] (dump_stack+0x84/0x94)
[<c04c84b8>] (dump_stack) from [<c001d8c0>] (warn_slowpath_common+0x6c/0x88)
[<c001d8c0>] (warn_slowpath_common) from [<c001d90c>] (warn_slowpath_fmt+0x30/0x40)
[<c001d90c>] (warn_slowpath_fmt) from [<c0104468>] (kernfs_remove_by_name_ns+0x80/0x88)
[<c0104468>] (kernfs_remove_by_name_ns) from [<c0394d98>] (of_update_property+0xc0/0xf0)
[<c0394d98>] (of_update_property) from [<c0647248>] (mvebu_timer_and_clk_init+0xfc/0x194)
[<c0647248>] (mvebu_timer_and_clk_init) from [<c0640934>] (start_kernel+0x218/0x350)
[<c0640934>] (start_kernel) from [<00008070>] (0x8070)
---[ end trace 3406ff24bd97382e ]---
Unable to handle kernel NULL pointer dereference at virtual address 0000003c
pgd = c0004000
[0000003c] *pgd=00000000
Internal error: Oops: 5 [#1] SMP ARM
Modules linked in:
CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W     3.15.0-rc1-00127-g1d7e7b2-dirty #423
task: c10ad4d8 ti: c10a2000 task.ti: c10a2000
PC is at kernfs_find_ns+0x8/0xf0
LR is at kernfs_find_and_get_ns+0x30/0x48
pc : [<c0103834>]    lr : [<c010394c>]    psr: 600001d3
sp : c10a3f34  ip : 00000073  fp : 00000000
r10: 00000000  r9 : cfffc240  r8 : cfdf2980
r7 : cf812c00  r6 : 00000000  r5 : 00000000  r4 : c10b45e0
r3 : c10ad4d8  r2 : 00000000  r1 : cf812c00  r0 : 00000000
Flags: nZCv  IRQs off  FIQs off  Mode SVC_32  ISA ARM  Segment kernel
Control: 10c53c7d  Table: 0000404a  DAC: 00000015
Process swapper/0 (pid: 0, stack limit = 0xc10a2240)
Stack: (0xc10a3f34 to 0xc10a4000)
3f20:                                              c10b45e0 00000000 00000000
3f40: cf812c00 c010394c 00000063 cf812c00 00000001 cf812c00 cfdf29ac c03932cc
3f60: 00000063 cf812bc0 cfdf29ac cf812c00 ffffffff c03943f8 cfdf2980 c0104468
3f80: cfdf2a04 cfdf2980 cf812bc0 c06634b0 c10aa3c0 c0394da4 c10f74dc cfdf2980
3fa0: cf812bc0 c0647248 c10aa3c0 ffffffff c10de940 c10aa3c0 ffffffff c0640934
3fc0: ffffffff ffffffff c06404ec 00000000 00000000 c06634b0 00000000 10c53c7d
3fe0: c10aa434 c06634ac c10ae4c8 0000406a 414fc091 00008070 00000000 00000000
[<c0103834>] (kernfs_find_ns) from [<00000001>] (0x1)
Code: e5c89001 eaffffcf e92d40f0 e1a06002 (e1d023bc)
---[ end trace 3406ff24bd97382f ]---
Kernel panic - not syncing: Attempted to kill the idle task!
---[ end Kernel panic - not syncing: Attempted to kill the idle task!

To fix this problem, we simply skip the sysfs related calls in
of_update_property(), and rely on of_init() to fix up things when it
will be called, exactly as is done in of_add_property() and
of_remove_property().

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Fixes: 75b57ecf9d ("of: Make device nodes kobjects so they show up in sysfs")
Signed-off-by: Grant Likely <grant.likely@linaro.org>

drivers/of/base.c

@@ -1831,6 +1831,10 @@ int of_update_property(struct device_node *np, struct property *newprop)
 	if (!found)
 		return -ENODEV;
 
+	/* At early boot, bail out and defer setup to of_init() */
+	if (!of_kset)
+		return found ? 0 : -ENODEV;
+
 	/* Update the sysfs attribute */
 	sysfs_remove_bin_file(&np->kobj, &oldprop->attr);
 	__of_add_property_sysfs(np, newprop);