Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965080AbbD0Snr (ORCPT ); Mon, 27 Apr 2015 14:43:47 -0400 Received: from mail-wg0-f50.google.com ([74.125.82.50]:35379 "EHLO mail-wg0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964801AbbD0Sno convert rfc822-to-8bit (ORCPT ); Mon, 27 Apr 2015 14:43:44 -0400 Subject: Re: [PATCH v3 2/4] of: overlay: global sysfs enable attribute Mime-Version: 1.0 (Mac OS X Mail 8.2 \(2098\)) Content-Type: text/plain; charset=utf-8 From: Pantelis Antoniou In-Reply-To: <20150427183915.GA29312@kroah.com> Date: Mon, 27 Apr 2015 21:43:39 +0300 Cc: Rob Herring , Grant Likely , Andrew Morton , Matt Porter , Koen Kooi , Guenter Roeck , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org Content-Transfer-Encoding: 8BIT Message-Id: <1B376CD2-6F5C-4357-9A17-43046079E5CD@konsulko.com> References: <1429868744-19863-1-git-send-email-pantelis.antoniou@konsulko.com> <1429868744-19863-3-git-send-email-pantelis.antoniou@konsulko.com> <20150424202922.GA14970@kroah.com> <355B6AF0-7F58-4BE4-BEE6-A77246D40652@konsulko.com> <20150427183915.GA29312@kroah.com> To: Greg KH X-Mailer: Apple Mail (2.2098) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4817 Lines: 152 Hi Greg, > On Apr 27, 2015, at 21:39 , Greg KH wrote: > > On Mon, Apr 27, 2015 at 09:13:56PM +0300, Pantelis Antoniou wrote: >> Hi Greg, >> >>> On Apr 24, 2015, at 23:29 , Greg KH wrote: >>> >>> On Fri, Apr 24, 2015 at 12:45:42PM +0300, Pantelis Antoniou wrote: >>>> A throw once master enable switch to protect against any >>>> further overlay applications if the administrator desires so. >>>> >>>> Signed-off-by: Pantelis Antoniou >>>> --- >>>> drivers/of/overlay.c | 45 ++++++++++++++++++++++++++++++++++++++++++++- >>>> 1 file changed, 44 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c >>>> index f17f5ef..c335809 100644 >>>> --- a/drivers/of/overlay.c >>>> +++ b/drivers/of/overlay.c >>>> @@ -21,6 +21,7 @@ >>>> #include >>>> #include >>>> #include >>>> +#include >>>> >>>> #include "of_private.h" >>>> >>>> @@ -55,8 +56,12 @@ struct of_overlay { >>>> struct kobject kobj; >>>> }; >>>> >>>> +/* master enable switch; once set to 0 can't be re-enabled */ >>>> +static atomic_t ov_enable = ATOMIC_INIT(1); >>>> + >>>> static int of_overlay_apply_one(struct of_overlay *ov, >>>> struct device_node *target, const struct device_node *overlay); >>>> +static int overlay_removal_is_ok(struct of_overlay *ov); >>>> >>>> static int of_overlay_apply_single_property(struct of_overlay *ov, >>>> struct device_node *target, struct property *prop) >>>> @@ -339,6 +344,37 @@ void of_overlay_release(struct kobject *kobj) >>>> kfree(ov); >>>> } >>>> >>>> +static ssize_t enable_show(struct kobject *kobj, >>>> + struct kobj_attribute *attr, char *buf) >>>> +{ >>>> + return snprintf(buf, PAGE_SIZE, "%d\n", atomic_read(&ov_enable)); >>>> +} >>>> + >>>> +static ssize_t enable_store(struct kobject *kobj, >>>> + struct kobj_attribute *attr, const char *buf, size_t count) >>>> +{ >>>> + int ret; >>>> + long new_enable; >>>> + >>>> + ret = kstrtol(buf, 10, &new_enable); >>>> + if (ret != 0) >>>> + return ret; >>>> + if ((unsigned long)new_enable > 1) >>>> + return -EINVAL; >>>> + /* if we've disabled it, no going back */ >>>> + if (atomic_read(&ov_enable) == 0) >>>> + return -EPERM; >>>> + atomic_set(&ov_enable, (int)new_enable); >>>> + return count; >>>> +} >>>> + >>>> +static struct kobj_attribute enable_attr = __ATTR_RW(enable); >>>> + >>>> +static const struct attribute *overlay_global_attrs[] = { >>>> + &enable_attr.attr, >>>> + NULL >>>> +}; >>> >>> Why not make this an attribute group and then attach it to the kobj_type >>> to create the files in a race-free manner? >>> >> >> Err, these are the global attributes. They are attached to the >> parent of the overlay objects which is a kset object itself. > > Ick, no, never attach attributes to a kobject that you don't create > yourself, otherwise it's a race that you lost. > Err, it is created by me. It’s a kset by the following call: > ov_kset = kset_create_and_add("overlays", NULL, &of_kset->kobj); > What is the problem with this? >>>> + >>>> static struct kobj_type of_overlay_ktype = { >>>> .release = of_overlay_release, >>>> }; >>>> @@ -360,6 +396,10 @@ int of_overlay_create(struct device_node *tree) >>>> struct of_overlay *ov; >>>> int err, id; >>>> >>>> + /* administratively disabled */ >>>> + if (!atomic_read(&ov_enable)) >>>> + return -EPERM; >>>> + >>>> /* allocate the overlay structure */ >>>> ov = kzalloc(sizeof(*ov), GFP_KERNEL); >>>> if (ov == NULL) >>>> @@ -596,5 +636,8 @@ int of_overlay_init(void) >>>> if (!ov_kset) >>>> return -ENOMEM; >>>> >>>> - return 0; >>>> + rc = sysfs_create_files(&ov_kset->kobj, overlay_global_attrs); >>>> + WARN(rc, "%s: error adding global attributes\n", __func__); >>> >>> What can a user do with this warning message? If nothing, then don't >>> print it out, right? >>> >>> You are creating sysfs files _after_ the kobject has been announced to >>> userspace, causing nasty race conditions. Please don't do that. >>> >> >> This is at overlay_init() time, which is way way before userspace ever >> has a chance to start. If there’s a different way to attach a attribute >> group to a kset object I’d like to find out how :) > > You can't load this as a module? Where exactly in sysfs is this > kobject, and who creates it? > No, there’s no way to load this as a module, it’s in /sys/firmware/devicetree And it’s created by the call to kset_create_and_add() > thanks, > > greg k-h Regards — Pantelis -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/