Re: proc_flush_task oops

[Dave Jones]

On Thu, Dec 21, 2017 at 07:31:26PM -0600, Eric W. Biederman wrote:
 > Dave Jones <davej@xxxxxxxxxxxxxxxxx> writes:
 > 
 > > On Thu, Dec 21, 2017 at 12:38:12PM +0200, Alexey Dobriyan wrote:
 > >  
 > >  > > with proc_mnt still set to NULL is a mystery to me.
 > >  > >
 > >  > > Is there any chance the idr code doesn't always return the lowest valid
 > >  > > free number?  So init gets assigned something other than 1?
 > >  > 
 > >  > Well, this theory is easy to test (attached).
 > >
 > > I didn't hit this BUG, but I hit the same oops in proc_flush_task.
 > 
 > Scratch one idea.
 > 
 > If it isn't too much trouble can you try this.
 > 
 > I am wondering if somehow the proc_mnt that is NULL is somewhere in the
 > middle of the stack of pid namespaces.
 > 
 > This adds two warnings.  The first just reports which pid namespace in
 > the stack of pid namespaces is problematic, and the pid number in that
 > pid namespace.  Which should give a whole lot more to go by.
 > 
 > The second warning complains if we manage to create a pid namespace
 > where the parent pid namespace is not properly set up.  The test to
 > prevent that looks quite robust, but at this point I don't know where to
 > look.

Progress ?

[ 1653.030190] ------------[ cut here ]------------
[ 1653.030852] 1/1: 2 no proc_mnt
[ 1653.030946] WARNING: CPU: 2 PID: 4420 at kernel/pid.c:213 alloc_pid+0x24f/0x2a0