linux-kernel - Re: [PATCH] sysfs: check if one entry has been removed before freeing

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Message-ID: <CACVXFVMV6cFhrybrE_oNSthzPF71xOE7dbwTK9GP+x08d3TpQA@mail.gmail.com>
Date:	Wed, 3 Apr 2013 15:05:37 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Dave Jones <davej@...hat.com>, linux-kernel@...r.kernel.org,
	Sasha Levin <levinsasha928@...il.com>
Subject: Re: [PATCH] sysfs: check if one entry has been removed before freeing

On Wed, Apr 3, 2013 at 1:35 PM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Wed, Apr 03, 2013 at 11:52:39AM +0800, Ming Lei wrote:
>> On Wed, Apr 3, 2013 at 11:04 AM, Dave Jones <davej@...hat.com> wrote:
>> > On Wed, Apr 03, 2013 at 10:58:23AM +0800, Ming Lei wrote:
>> >
>> >  > diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
>> >  > index 1bf016b..328ef9b 100644
>> >  > --- a/fs/sysfs/dir.c
>> >  > +++ b/fs/sysfs/dir.c
>> >  > @@ -268,6 +268,13 @@ void release_sysfs_dirent(struct sysfs_dirent * sd)
>> >  >       */
>> >  >      parent_sd = sd->s_parent;
>> >  >
>> >  > +    if (unlikely(!(sd->s_flags & SYSFS_FLAG_REMOVED))) {
>> >  > +            printk(KERN_ERR "sysfs: free using entry: %s/%s\n",
>> >  > +                    parent_sd ? parent_sd->s_name : "",
>> >  > +                    sd->s_name);
>> >  > +            BUG();
>> >  > +    }
>> >
>> > Please use WARN instead of BUG.  For an in-ram filesystem like
>> > sysfs, there's no real reason to lock-up the machine in this way
>> > making it harder to debug.
>>
>> If WARN is used, the freed memory will be allocated to other
>> kernel components, then sysfs may change the memory and cause
>> destruction, so maybe it is better to use BUG to stop kernel.
>
> No, it's never ok to call BUG(), sorry, please fix this.

Sorry, could you explain it in a bit detail? IMO, it is really a bug
when code runs here, and there are much similar BUG_ON()
uses in current sysfs code too.

Thanks,
--
Ming Lei
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