Re: [PATCH 02/18] mm: memcontrol: fix theoretical race in charge moving

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Mon, Apr 20, 2020 at 06:11:10PM -0400, Johannes Weiner wrote:
> The move_lock is a per-memcg lock, but the VM accounting code that
> needs to acquire it comes from the page and follows page->mem_cgroup
> under RCU protection. That means that the page becomes unlocked not
> when we drop the move_lock, but when we update page->mem_cgroup. And
> that assignment doesn't imply any memory ordering. If that pointer
> write gets reordered against the reads of the page state -
> page_mapped, PageDirty etc. the state may change while we rely on it
> being stable and we can end up corrupting the counters.
> 
> Place an SMP memory barrier to make sure we're done with all page
> state by the time the new page->mem_cgroup becomes visible.
> 
> Also replace the open-coded move_lock with a lock_page_memcg() to make
> it more obvious what we're serializing against.
> 
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Reviewed-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>

Thanks.



[Index of Archives]     [Linux ARM Kernel]     [Linux ARM]     [Linux Omap]     [Fedora ARM]     [IETF Annouce]     [Security]     [Bugtraq]     [Linux OMAP]     [Linux MIPS]     [eCos]     [Asterisk Internet PBX]     [Linux API]     [Monitors]

  Powered by Linux