Re: [bug report] mm: reduce noise in show_mem for lowmem allocations

[Dan Carpenter <dan.carpenter@oracle.com>]

On Tue, Aug 30, 2022 at 08:46:58AM +0200, Michal Hocko wrote:
> On Tue 30-08-22 09:30:26, Dan Carpenter wrote:
> > Hello Michal Hocko,
> > 
> > The patch e8fedfea3dea: "mm: reduce noise in show_mem for lowmem
> > allocations" from Aug 23, 2022, leads to the following Smatch static
> > checker warning:
> > 
> > 	kernel/panic.c:190 panic_print_sys_info()
> > 	warn: sleeping in atomic context
> 
> What is this warning saying?
> 

This is a Smatch warning.

> >     189         if (panic_print & PANIC_PRINT_MEM_INFO)
> > --> 190                 show_mem(0, NULL, GFP_HIGHUSER_MOVABLE);
> >                                           ^^^^^^^^^^^^^^^^^^^^
> > This obviously seems very deliberate and a lot of weird stuff happens
> > during panic().  But the panic() function disables preemption so
> > shouldn't this be GFP_ATOMIC?  GFP_HIGHUSER_MOVABLE has __GFP_RECLAIM
> > and triggering swap during a panic seems bad.
> 
> This function shouldn't ever be allocating any memory. The flag is
> solely to infer which memory zones should be displayed. It acts as a
> filter. Is it possible that the checker misinterprets the parameter's
> meaning?

Ah.  Yes.  Smatch sees every gfp_t as a sleep/no sleep marker.  I
didn't realize it wasn't used like that here.  Thanks!

regards,
dan carpenter