Re: Possible memory leak via alloc_pid()

[Serge E. Hallyn]

Quoting Andrew Morton (akpm@xxxxxxxxxxxxxxxxxxxx):
> On Wed, 8 Jul 2009 22:33:31 +0100
> Catalin Marinas <catalin.marinas@xxxxxxx> wrote:
> 
> > Hi,
> > 
> > There's a kmemleak report of a struct pid allocation in alloc_pid()
> > which somehow gets lost:
> > 
> > unreferenced object 0xc307aa00 (size 44):
> >   comm "gdm", pid 2734, jiffies 4294902040
> >   backtrace:
> >     [<c01e721a>] create_object+0xfa/0x250
> >     [<c01e73cd>] kmemleak_alloc+0x5d/0x70
> >     [<c01e0ad6>] kmem_cache_alloc+0x156/0x1a0
> >     [<c01552f9>] alloc_pid+0x19/0x350
> >     [<c013e6e0>] copy_process+0x800/0x1230
> >     [<c013f17f>] do_fork+0x6f/0x370
> >     [<c0101986>] sys_clone+0x36/0x40
> >     [<c010319c>] sysenter_do_call+0x12/0x38
> >     [<ffffffff>] 0xffffffff
> > 
> > This is the gdm fork for starting Xorg (with pid 2739). It first
> > logged me in automatically, after which I logged out and gdm started
> > another Xorg. The pid structure for the first Xorg is reported as a
> > leak. The Xorg with pid 2739 is no longer present on my system.
> > 
> > Using gdb vmlinux /proc/kcore shows that the pid->count is 2, so
> > that's why it probably wasn't freed by put_pid():
> > 
> > (gdb) print ({struct pid}0xc307aa00)
> > $20 = {count = {counter = 2}, level = 0, tasks = {{first = 0x0}, {
> >       first = 0x0}, {first = 0x0}}, rcu = {next = 0xc24bfd64,
> >     func = 0xc0154e90 <delayed_put_pid>}, numbers = {{nr = 2739,
> >       ns = 0xc0737540, pid_chain = {next = 0x0, pprev = 0x200200}}}}
> > 
> > Note that kmemleak is aware of and scans pid_hash (which was recorded
> > in kmemleak as a 16KB object).
> > 
> 
> Thanks.  Let's cc some recent pid fiddlers.

Hi,

thanks for the report.  Note that kernel modules can increment those
counds through find_get_pid().  Can you send your kernel .config and
the output of lsmod?

thanks,
-serge
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