2020-05-04 03:41:43

by Kevin Hao

[permalink] [raw]
Subject: [PATCH v5.6-rt] mm: slub: Always flush the delayed empty slubs in flush_all()

After commit f0b231101c94 ("mm/SLUB: delay giving back empty slubs to
IRQ enabled regions"), when the free_slab() is invoked with the IRQ
disabled, the empty slubs are moved to a per-CPU list and will be
freed after IRQ enabled later. But in the current codes, there is
a check to see if there really has the cpu slub on a specific cpu
before flushing the delayed empty slubs, this may cause a reference
of already released kmem_cache in a scenario like below:
cpu 0 cpu 1
kmem_cache_destroy()
flush_all()
--->IPI flush_cpu_slab()
flush_slab()
deactivate_slab()
discard_slab()
free_slab()
c->page = NULL;
for_each_online_cpu(cpu)
if (!has_cpu_slab(1, s))
continue
this skip to flush the delayed
empty slub released by cpu1
kmem_cache_free(kmem_cache, s)

kmalloc()
__slab_alloc()
free_delayed()
__free_slab()
reference to released kmem_cache

Fixes: f0b231101c94 ("mm/SLUB: delay giving back empty slubs to IRQ enabled regions")
Signed-off-by: Kevin Hao <[email protected]>
---
mm/slub.c | 3 ---
1 file changed, 3 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 15c194ff16e6..83b29bf71fd0 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2402,9 +2402,6 @@ static void flush_all(struct kmem_cache *s)
for_each_online_cpu(cpu) {
struct slub_free_list *f;

- if (!has_cpu_slab(cpu, s))
- continue;
-
f = &per_cpu(slub_free_list, cpu);
raw_spin_lock_irq(&f->lock);
list_splice_init(&f->list, &tofree);
--
2.26.0


Subject: Re: [PATCH v5.6-rt] mm: slub: Always flush the delayed empty slubs in flush_all()

On 2020-05-04 11:34:07 [+0800], Kevin Hao wrote:
> After commit f0b231101c94 ("mm/SLUB: delay giving back empty slubs to
…
> Fixes: f0b231101c94 ("mm/SLUB: delay giving back empty slubs to IRQ enabled regions")
> Signed-off-by: Kevin Hao <[email protected]>

Applied, thanks.

Sebastian

2020-05-04 21:26:55

by David Rientjes

[permalink] [raw]
Subject: Re: [PATCH v5.6-rt] mm: slub: Always flush the delayed empty slubs in flush_all()

On Mon, 4 May 2020, Kevin Hao wrote:

> After commit f0b231101c94 ("mm/SLUB: delay giving back empty slubs to
> IRQ enabled regions"), when the free_slab() is invoked with the IRQ
> disabled, the empty slubs are moved to a per-CPU list and will be
> freed after IRQ enabled later. But in the current codes, there is
> a check to see if there really has the cpu slub on a specific cpu
> before flushing the delayed empty slubs, this may cause a reference
> of already released kmem_cache in a scenario like below:
> cpu 0 cpu 1
> kmem_cache_destroy()
> flush_all()
> --->IPI flush_cpu_slab()
> flush_slab()
> deactivate_slab()
> discard_slab()
> free_slab()
> c->page = NULL;
> for_each_online_cpu(cpu)
> if (!has_cpu_slab(1, s))
> continue
> this skip to flush the delayed
> empty slub released by cpu1
> kmem_cache_free(kmem_cache, s)
>
> kmalloc()
> __slab_alloc()
> free_delayed()
> __free_slab()
> reference to released kmem_cache
>
> Fixes: f0b231101c94 ("mm/SLUB: delay giving back empty slubs to IRQ enabled regions")
> Signed-off-by: Kevin Hao <[email protected]>

Acked-by: David Rientjes <[email protected]>