> -----Original Message----- > From: Andrew Jeffery [mailto:andrew@xxxxxxxx] > Sent: Thursday, July 27, 2017 9:01 AM > To: Mykola Kostenok <c_mykolak@xxxxxxxxxxxx>; Joel Stanley > <joel@xxxxxxxxx> > Cc: linux-hwmon@xxxxxxxxxxxxxxx; Jaghathiswari Rankappagounder > Natarajan <jaghu@xxxxxxxxxx>; Jean Delvare <jdelvare@xxxxxxxx>; Ohad > Oz <ohado@xxxxxxxxxxxx>; Vadim Pasternak <vadimp@xxxxxxxxxxxx>; > Patrick Venture <venture@xxxxxxxxxx>; OpenBMC Maillist > <openbmc@xxxxxxxxxxxxxxxx>; Rob Herring <robh+dt@xxxxxxxxxx>; Guenter > Roeck <linux@xxxxxxxxxxxx> > Subject: Re: [patch v3] hwmon: (aspeed-pwm-tacho) cooling device support. > > Hi Mykola, > > I know you've sent out subsequent versions, but I wanted to address one of > your arguments here: > > On Wed, 2017-07-26 at 11:08 +0000, Mykola Kostenok wrote: > > > > @@ -834,10 +946,12 @@ static int aspeed_pwm_tacho_probe(struct > > > > platform_device *pdev) > > > > > > > > for_each_child_of_node(np, child) { > > > > ret = aspeed_create_fan(dev, child, priv); > > > > - of_node_put(child); > > > > - if (ret) > > > > + if (ret) { > > > > + of_node_put(child); > > > > return ret; > > > > + } > > > > } > > > > + of_node_put(child); > > > > > > I'm not sure about these. > > > > > > Cheers, > > > > > > Joel > > > > If CONFIG_OF_UNITTEST is set, system initialization fails on this > of_node_put. > > I checked and found that for_each_child_of_node is macro witch use > > __of_get_next_child > > in cycle. __of_get_next_child do of_node_put previous child but not last. > > > > static struct device_node *__of_get_next_child(const struct > > device_node *node, > > struct device_node > > *prev) { > > struct device_node *next; > > > > if (!node) > > return NULL; > > > > next = prev ? prev->sibling : node->child; > > for (; next; next = next->sibling) > > if (of_node_get(next)) > > break; > > of_node_put(prev); > > return next; > > } > > #define __for_each_child_of_node(parent, child) \ > > for (child = __of_get_next_child(parent, NULL); child != NULL; > > \ > > child = __of_get_next_child(parent, child)) > > > > So inside cycle we should not use of_node_put on each child. We must use > it only on last child in cycle. > > I was just looking at this myself for a different driver, and I don't think this > argument is right. The natural terminating condition of the loop is child == > NULL. child == NULL occurs if we have zero-or-more- children; the child is > always initialised as part of the loop header and would be NULL if there are > no children. If we have more than one child, the reference to the last valid > child is passed to of_node_put() in __of_get_next_child() in order to return > the terminating NULL. Given > __of_get_next_child() is passed the last node and the result is NULL, the call > to of_node_put() after the loop is always invoked on NULL, which performs > an early return. > > As such I think it is unnecessary. > > Cheers, > > Andrew Ok, I agree that we don’t need of_node_put after loop. We must do of_node_put only in case of error. So I will send next patch v6 with this: for_each_child_of_node(np, child) { ret = aspeed_create_fan(dev, child, priv); - of_node_put(child); - if (ret) + if (ret) { + of_node_put(child); return ret; + } } Without it and with CONFIG_OF_UNITTEST we see this: [ 3.000000] [<80010080>] (unwind_backtrace) from [<8000d934>] (show_stack+0x20/0x24) [ 3.000000] [<8000d934>] (show_stack) from [<801dbf8c>] (dump_stack+0x20/0x28) [ 3.000000] [<801dbf8c>] (dump_stack) from [<8030ad14>] (of_node_release+0x98/0xa0) [ 3.000000] [<8030ad14>] (of_node_release) from [<801de0ec>] (kobject_put+0xf8/0x1ec) [ 3.000000] [<801de0ec>] (kobject_put) from [<8030a340>] (of_node_put+0x24/0x28) [ 3.000000] [<8030a340>] (of_node_put) from [<80305fe4>] (__of_get_next_child+0x58/0x70) [ 3.000000] [<80305fe4>] (__of_get_next_child) from [<8030668c>] (of_get_next_child+0x20/0x28) [ 3.000000] [<8030668c>] (of_get_next_child) from [<802e39ac>] (aspeed_pwm_tacho_probe+0x490/0x574) [ 3.000000] [<802e39ac>] (aspeed_pwm_tacho_probe) from [<80244090>] (platform_drv_probe+0x60/0xc0) [ 3.000000] [<80244090>] (platform_drv_probe) from [<80242408>] (driver_probe_device+0x280/0x44c) [ 3.000000] [<80242408>] (driver_probe_device) from [<802426c4>] (__driver_attach+0xf0/0x104) [ 3.000000] [<802426c4>] (__driver_attach) from [<802403d8>] (bus_for_each_dev+0x7c/0xb0) [ 3.000000] [<802403d8>] (bus_for_each_dev) from [<8024286c>] (driver_attach+0x28/0x30) [ 3.000000] [<8024286c>] (driver_attach) from [<80240e38>] (bus_add_driver+0x14c/0x268) [ 3.000000] [<80240e38>] (bus_add_driver) from [<802432f8>] (driver_register+0x88/0x104) [ 3.000000] [<802432f8>] (driver_register) from [<80244cd0>] (__platform_driver_register+0x40/0x54) [ 3.000000] [<80244cd0>] (__platform_driver_register) from [<805bfc64>] (aspeed_pwm_tacho_driver_init+0x18/0x20) [ 3.000000] [<805bfc64>] (aspeed_pwm_tacho_driver_init) from [<8059de70>] (do_one_initcall+0xac/0x168) [ 3.000000] [<8059de70>] (do_one_initcall) from [<8059e040>] (kernel_init_freeable+0x114/0x1cc) [ 3.000000] [<8059e040>] (kernel_init_freeable) from [<804072a0>] (kernel_init+0x18/0x104) [ 3.000000] [<804072a0>] (kernel_init) from [<8000a5e8>] (ret_from_fork+0x14/0x2c) [ 3.200000] OF: ERROR: Bad of_node_put() on /ahb/apb/pwm-tacho-controller@1e786000/fan@1 And kernel panic at the end. Best regards. Mykola Kostenok. ��.n��������+%������w��{.n�����{��&��^n�r������&��z�ޗ�zf���h���~����������_��+v���)ߣ�