linux-kernel - Re: [PATCH v3 1/3] msi: free msi_desc entry only after we've released the kobject

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Message-ID: <CA+55aFxt9KnmZnK5QdkPcpHNR+Ath5WTzhRibu5Y=xOhiz3fzA@mail.gmail.com>
Date:	Tue, 29 Oct 2013 09:34:28 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Veaceslav Falico <vfalico@...hat.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Yinghai Lu <yinghai@...nel.org>,
	Knut Petersen <Knut_Petersen@...nline.de>,
	Ingo Molnar <mingo@...nel.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Neil Horman <nhorman@...driver.com>
Subject: Re: [PATCH v3 1/3] msi: free msi_desc entry only after we've released
 the kobject

On Tue, Oct 29, 2013 at 3:30 AM, Veaceslav Falico <vfalico@...hat.com> wrote:
>                 /*
>                  * Its possible that we get into this path
>                  * When populate_msi_sysfs fails, which means the entries
>                  * were not registered with sysfs.  In that case don't
> -                * unregister them.
> +                * unregister them, and just free. Otherwise the
> +                * kobject->release will take care of freeing the entry via
> +                * msi_kobj_release().
>                  */
>                 if (entry->kobj.parent) {
>                         kobject_del(&entry->kobj);
>                         kobject_put(&entry->kobj);
> +               } else {
> +                       kfree(entry);
>                 }
> -
> -               list_del(&entry->list);
> -               kfree(entry);

So this code sequence still makes me very unhappy.

Why does not just a simple unconditional

        kobject_del(&entry->kobj);
        kobject_put(&entry->kobj);

work for the "not registered with sysfs" case? And if the sysfs code
really gets confused, why not

        if (entry->kobj.parent)
                kobject_del(&entry->kobj);
        kobject_put(&entry->kobj);

(btw, looking at the sysfs code, this looks *very* suspicious in
sysfs_remove_dir():

        struct sysfs_dirent *sd = kobj->sd;

        spin_lock(&sysfs_assoc_lock);
        kobj->sd = NULL;
        spin_unlock(&sysfs_assoc_lock);

and I would suggest that "sd = kobj->sd" should be done under the
lock, because otherwise the lock is kind of pointless..)

Greg?

                Linus
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