Re: [PATCH 0/5] SLUB debugfs improvements based on stackdepot

[Mike Rapoport]

On Mon, Feb 28, 2022 at 09:27:02PM +0000, Hyeonggon Yoo wrote:
> On Mon, Feb 28, 2022 at 08:10:18PM +0100, Vlastimil Babka wrote:
> > On 2/26/22 08:19, Hyeonggon Yoo wrote:
> > > On Fri, Feb 25, 2022 at 07:03:13PM +0100, Vlastimil Babka wrote:
> > >> Hi,
> > >> 
> > >> this series combines and revives patches from Oliver's last year
> > >> bachelor thesis (where I was the advisor) that make SLUB's debugfs
> > >> files alloc_traces and free_traces more useful.
> > >> The resubmission was blocked on stackdepot changes that are now merged,
> > >> as explained in patch 2.
> > >> 
> > > 
> > > Hello. I just started review/testing this series.
> > > 
> > > it crashed on my system (arm64)
> > 
> > Hmm, interesting. On x86_64 this works for me and stackdepot is allocated
> > from memblock. arm64 must have memblock freeing happen earlier or something.
> > (CCing memblock experts)
> > 
> > > I ran with boot parameter slub_debug=U, and without KASAN.
> > > So CONFIG_STACKDEPOT_ALWAYS_INIT=n.
> > > 
> > > void * __init memblock_alloc_try_nid(
> > >                         phys_addr_t size, phys_addr_t align,
> > >                         phys_addr_t min_addr, phys_addr_t max_addr,
> > >                         int nid)
> > > {
> > >         void *ptr;
> > > 
> > >         memblock_dbg("%s: %llu bytes align=0x%llx nid=%d from=%pa max_addr=%pa %pS\n",
> > >                      __func__, (u64)size, (u64)align, nid, &min_addr,
> > >                      &max_addr, (void *)_RET_IP_);
> > >         ptr = memblock_alloc_internal(size, align,
> > >                                            min_addr, max_addr, nid, false);
> > >         if (ptr)
> > >                 memset(ptr, 0, size); <--- Crash Here
> > > 
> > >         return ptr;
> > > }
> > > 
> > > It crashed during create_boot_cache() -> stack_depot_init() ->
> > > memblock_alloc().
> > > 
> > > I think That's because, in kmem_cache_init(), both slab and memblock is not
> > > available. (AFAIU memblock is not available after mem_init() because of
> > > memblock_free_all(), right?)
> > 
> > Hm yes I see, even in x86_64 version mem_init() calls memblock_free_all().
> > But then, I would expect stack_depot_init() to detect that memblock_alloc()
> > returns NULL, we print ""Stack Depot hash table allocation failed,
> > disabling" and disable it. Instead it seems memblock_alloc() returns
> > something that's already potentially used by somebody else? Sounds like a bug?
> 
> 
> By the way, I fixed this by allowing stack_depot_init() to be called in
> kmem_cache_init() too [1] and Marco suggested that calling
> stack_depot_init() depending on slub_debug parameter for simplicity. [2]
> 
> I would prefer [2], Would you take a look?
> 
> [1] https://lkml.org/lkml/2022/2/27/31
> 
> [2] https://lkml.org/lkml/2022/2/28/717

I have the third version :)

diff --git a/mm/slub.c b/mm/slub.c
index a74afe59a403..0c3ab2335b46 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1548,6 +1548,10 @@ static int __init setup_slub_debug(char *str)
 	}
 out:
 	slub_debug = global_flags;
+
+	if (slub_flags & SLAB_STORE_USER && IS_ENABLED(CONFIG_STACKDEPOT))
+		stack_depot_early_init();
+
 	if (slub_debug != 0 || slub_debug_string)
 		static_branch_enable(&slub_debug_enabled);
 	else
@@ -4221,9 +4225,6 @@ static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
 	s->remote_node_defrag_ratio = 1000;
 #endif
 
-	if (s->flags & SLAB_STORE_USER && IS_ENABLED(CONFIG_STACKDEPOT))
-		stack_depot_init();
-
 	/* Initialize the pre-computed randomized freelist if slab is up */
 	if (slab_state >= UP) {
 		if (init_cache_random_seq(s))
 
> -- 
> Thank you, You are awesome!
> Hyeonggon :-)

-- 
Sincerely yours,
Mike.