Re: [PATCH v2 sl-b 3/5] mm: Make mem_dump_obj() handle vmalloc() memory

[Paul E. McKenney]

On Wed, Dec 09, 2020 at 06:51:20PM +0100, Vlastimil Babka wrote:
> On 12/9/20 2:13 AM, paulmck@xxxxxxxxxx wrote:
> > From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
> > 
> > This commit adds vmalloc() support to mem_dump_obj().  Note that the
> > vmalloc_dump_obj() function combines the checking and dumping, in
> > contrast with the split between kmem_valid_obj() and kmem_dump_obj().
> > The reason for the difference is that the checking in the vmalloc()
> > case involves acquiring a global lock, and redundant acquisitions of
> > global locks should be avoided, even on not-so-fast paths.
> > 
> > Note that this change causes on-stack variables to be reported as
> > vmalloc() storage from kernel_clone() or similar, depending on the degree
> > of inlining that your compiler does.  This is likely more helpful than
> > the earlier "non-paged (local) memory".
> > 
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> > Cc: <linux-mm@xxxxxxxxx>
> > Reported-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> 
> ...
> 
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -3431,6 +3431,18 @@ void pcpu_free_vm_areas(struct vm_struct **vms, int nr_vms)
> >  }
> >  #endif	/* CONFIG_SMP */
> >  
> > +bool vmalloc_dump_obj(void *object)
> > +{
> > +	struct vm_struct *vm;
> > +	void *objp = (void *)PAGE_ALIGN((unsigned long)object);
> > +
> > +	vm = find_vm_area(objp);
> > +	if (!vm)
> > +		return false;
> > +	pr_cont(" vmalloc allocated at %pS\n", vm->caller);
> 
> Would it be useful to print the vm area boundaries too?

Like this?

I also considered instead using vm->size, but that always seems to include
an extra page, so a 4-page span is listed as having 20480 bytes and a
one-page span is 8192 bytes.  This might be more accurate in some sense,
but would be quite confusing to someone trying to compare this size with
that requested in the vmalloc() call.

							Thanx, Paul

------------------------------------------------------------------------

commit 33e0469c289c2f78e5f0d0c463c8ee3357d273c0
Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
Date:   Wed Dec 9 15:15:27 2020 -0800

    mm: Make mem_obj_dump() vmalloc() dumps include start and length
    
    This commit adds the starting address and number of pages to the vmalloc()
    information dumped by way of vmalloc_dump_obj().
    
    Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
    Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
    Cc: <linux-mm@xxxxxxxxx>
    Reported-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
    Suggested-by: Vlastimil Babka <vbabka@xxxxxxx>
    Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 7421719..77b1100 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3439,7 +3439,8 @@ bool vmalloc_dump_obj(void *object)
 	vm = find_vm_area(objp);
 	if (!vm)
 		return false;
-	pr_cont(" vmalloc allocated at %pS\n", vm->caller);
+	pr_cont(" %u-page vmalloc region starting at %#lx allocated at %pS\n",
+		vm->nr_pages, (unsigned long)vm->addr, vm->caller);
 	return true;
 }