Re: Possible memory leak via alloc_pid()

[Catalin Marinas <catalin.marinas@arm.com>]

On Sun, 2009-08-02 at 18:44 -0700, Eric W. Biederman wrote:
> Hmm.  I'm starting to wonder if kmemleak is right.  I don't know how
> it works but something about the way pids are used might be confusing it.

It could as well be a false positive but I can't find its source.

Basically, the pid structure for the dead Xorg is still allocated
minutes after Xorg died with a pid->count of 2. Kmemleak scans the data
and bss sections, task stacks and most of the allocated objects (which
are not reported as leaks) but cannot find a pointer to this pid
structure (or anywhere inside it like pid->number.pid_chain).

The supposedly leaked pid structure also have pid_chain.pprev ==
LIST_POISON2 which means that it was already removed from the pid_hash
(this block of memory is scanned by kmemleak anyway).

The free_pid() function was also called on this object according to the
pid->rcu values but put_pid() couldn't free it because of pid->count.

If this structure in not on pid_hash, is there any other place where its
pointer may be stored for a long time? Otherwise it looks like a real
leak (though not a big one).

I'll do more tests in the next few days as suggested by Oleg.

-- 
Catalin