Re: [PATCH v2 2/2] mm/vmalloc: Print a warning message first on failure

[Matthew Wilcox]

On Sun, May 09, 2021 at 10:05:19PM +0200, Uladzislau Rezki wrote:
> On Sun, May 09, 2021 at 08:47:12PM +0100, Matthew Wilcox wrote:
> > > +++ b/mm/vmalloc.c
> > > @@ -2781,11 +2781,11 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
> > >  	}
> > >  
> > >  	if (!area->pages) {
> > > -		free_vm_area(area);
> > >  		warn_alloc(gfp_mask, NULL,
> > >  			   "vmalloc size %lu allocation failure: "
> > >  			   "page array size %lu allocation failed",
> > >  			   nr_small_pages * PAGE_SIZE, array_size);
> > > +		free_vm_area(area);
> > >  		return NULL;
> > >  	}
> > 
> > I think this is a bad idea.  We're clearly low on memory (a memory
> > allocation just failed).  We should free the memory we have allocated
> > to improve the chances of the warning message making it out.
> Not sure if i fully follow you here. We do free the memory. The intention
> was to print a warning message first because, if, potentially, the
> free_vm_area(area) also does some prints it would be a bit messy from the
> point what has been broken first.
> 
> So, could you please clarify what was your concern?

We may need to allocate memory in order to emit the error message.
Your commit message didn't mention the potential confusion, and I think
that is worth adding for a v4.