On Tue, 2021-08-10 at 11:03 +0200, Vlastimil Babka wrote:
> On 8/9/21 3:41 PM, Qian Cai wrote:
> > >
> > > +static DEFINE_MUTEX(flush_lock);
> > > +static DEFINE_PER_CPU(struct slub_flush_work, slub_flush);
> > > +
> > > static void flush_all(struct kmem_cache *s)
> > > {
> > > - on_each_cpu_cond(has_cpu_slab, flush_cpu_slab, s, 1);
> > > + struct slub_flush_work *sfw;
> > > + unsigned int cpu;
> > > +
> > > + mutex_lock(&flush_lock);
> >
> > Vlastimil, taking the lock here could trigger a warning during memory offline/online due to the locking order:
> >
> > slab_mutex -> flush_lock
> >
> > [ 91.374541] WARNING: possible circular locking dependency detected
> > [ 91.381411] 5.14.0-rc5-next-20210809+ #84 Not tainted
> > [ 91.387149] ------------------------------------------------------
> > [ 91.394016] lsbug/1523 is trying to acquire lock:
> > [ 91.399406] ffff800018e76530 (flush_lock){+.+.}-{3:3}, at: flush_all+0x50/0x1c8
> > [ 91.407425]
> > but task is already holding lock:
> > [ 91.414638] ffff800018e48468 (slab_mutex){+.+.}-{3:3}, at: slab_memory_callback+0x44/0x280
> > [ 91.423603]
> > which lock already depends on the new lock.
> >
>
> OK, managed to reproduce in qemu and this fixes it for me on top of
> next-20210809. Could you test as well, as your testing might be more
> comprehensive? I will format is as a fixup for the proper patch in the series then.
As it appeared it should, moving cpu_hotplug_lock outside slab_mutex in
kmem_cache_destroy() on top of that silenced the cpu offline gripe.
---
mm/slab_common.c | 2 ++
mm/slub.c | 2 +-
2 files changed, 3 insertions(+), 1 deletion(-)
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -502,6 +502,7 @@ void kmem_cache_destroy(struct kmem_cach
if (unlikely(!s))
return;
+ cpus_read_lock();
mutex_lock(&slab_mutex);
s->refcount--;
@@ -516,6 +517,7 @@ void kmem_cache_destroy(struct kmem_cach
}
out_unlock:
mutex_unlock(&slab_mutex);
+ cpus_read_unlock();
}
EXPORT_SYMBOL(kmem_cache_destroy);
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4234,7 +4234,7 @@ int __kmem_cache_shutdown(struct kmem_ca
int node;
struct kmem_cache_node *n;
- flush_all(s);
+ flush_all_cpus_locked(s);
/* Attempt to free all objects */
for_each_kmem_cache_node(s, node, n) {
free_partial(s, n);
