Re: [PATCH] cfg80211: clear cfg80211_inform_bss() from kmemleak reports

From: Luis R. Rodriguez
Date: Fri Sep 04 2009 - 17:22:12 EST

On Fri, Sep 4, 2009 at 1:25 AM, Catalin Marinas<catalin.marinas@xxxxxxx> wrote:
> On Fri, 2009-09-04 at 07:04 +0200, Johannes Berg wrote:
>> On Thu, 2009-09-03 at 13:43 -0700, Luis R. Rodriguez wrote:
>> > On Thu, Sep 03, 2009 at 11:17:17AM -0700, Johannes Berg wrote:
>> > > On Thu, 2009-09-03 at 11:13 -0700, Luis R. Rodriguez wrote:
>> > >
>> > > > What I meant is it gobbles it up and spits another thing out. When it
>> > > > gobbles it up the routine then uses kref_put().
>> > > >
>> > > > > Why can it not track this?
>> > > >
>> > > > It probably can, just not sure if it follows kref_put(), I was under
>> > > > the impression here it doesn't and because of it we were getting false
>> > > > positives. Catalin, can you confirm?
>> > >
>> > > Ah I'd think that if it can't track it then that's because we use a
>> > > pointer to the middle of the struct to keep track of it much of the
>> > > time.
>> >
>> > So you agree with the patch but not the commit log entry?
>> I'm not sure -- I think kmemleak should be able to figure it out, and if
>> you were using IBSS then we actually have a leak that we need to plug,
>> but otherwise I'd prefer to get some more input from Catalin first.
> First of all, kmemleak_ignore() is not the right function to mark a
> false positive as it completely ignores an object even though it may
> have pointers to others. The kmemleak_not_leak() function should be
> used. However, there are only two places in the kernel where this was
> actually needed (one of them is a real leak but we ignore it as it makes
> the code more complicated).
> So, I think we should try to figure out why kmemleak reports it. There
> are a few common cases:
> Â Â 1. transient false positive - this should disappear after a few
> Â Â Â Âscans
> Â Â 2. a pointer leading to the reported object is stored in an area of
> Â Â Â Âmemory not scanned by kmemleak - most commonly pages allocated
> Â Â Â Âexplicitly (alloc_pages etc.) as kmemleak doesn't track these.
> Â Â Â ÂThe preferred solution is to inform kmemleak about such page
> Â Â Â Â(kmemleak_alloc/kmemleak_free) rather than marking the false
> Â Â Â Âpositive
> Â Â 3. a pointer leading to the reported object isn't actually pointing
> Â Â Â Âto anywhere inside the structure (i.e. using the physical
> Â Â Â Âaddress). Here we would use kmemleak_not_leak()

John please revert this merged patch
(b563f91105758c35d7cd4589992198b9da52d579) on wireless-testing as we'd
like to investigate further why we get this.

BTW I should not I got this kmemleak report after using the clear
command by painting objects black. I'll test it now with your
suggested changes.

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