Re: [PATCH] mm/slab_common: fix possiable double free of kmem_cache

[Waiman Long]

On 9/19/22 08:50, Feng Tang wrote:
> On Mon, Sep 19, 2022 at 05:12:38PM +0800, Vlastimil Babka wrote:
> > On 9/19/22 05:12, Feng Tang wrote:
> [...]
> > > The cause is inside kmem_cache_destroy():
> > >
> > > kmem_cache_destroy
> > >      acquire lock/mutex
> > >      shutdown_cache
> > >          schedule_work(kmem_cache_release) (if RCU flag set)
> > >      release lock/mutex
> > >      kmem_cache_release (if RCU flag set)
> > 				      ^ not set
> >
> > I've fixed that up.
> Oops.. Thanks for catching it!
>
> > > in some certain timing, the scheduled work could be run before
> > > the next RCU flag checking which will get a wrong state.
> > >
> > > Fix it by caching the RCU flag inside protected area, just like 'refcnt'
> > >
> > > Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>
> > Thanks!
> >
> > > ---
> > >
> > > note:
> > >
> > > The error only happens on linux-next tree, and not in Linus' tree,
> > > which already has Waiman's commit:
> > > 0495e337b703 ("mm/slab_common: Deleting kobject in kmem_cache_destroy()
> > > without holding slab_mutex/cpu_hotplug_lock")
> > Actually that commit is already in Linus' rc5 too, so I will send your fix
> > this week too. Added a Fixes: 0495e337b703 (...) too.
> Got it, thanks
>
> - Feng

Thanks for catching this bug.

Reviewed-by: Waiman Long <longman@xxxxxxxxxx>

Cheers,
Longman