On Fri 17-07-20 00:12:15, Tetsuo Handa wrote:
> syzbot is reporting that mmput() from shrinker function has a risk of
> deadlock [1], for delayed_uprobe_add() from update_ref_ctr() calls
> kzalloc(GFP_KERNEL) with delayed_uprobe_lock held, and
> uprobe_clear_state() from __mmput() also holds delayed_uprobe_lock.
>
> Commit a1b2289cef92ef0e ("android: binder: drop lru lock in isolate
> callback") replaced mmput() with mmput_async() in order to avoid sleeping
> with spinlock held. But this patch replaces mmput() with mmput_async() in
> order not to start __mmput() from shrinker context.
>
> [1] https://syzkaller.appspot.com/bug?id=bc9e7303f537c41b2b0cc2dfcea3fc42964c2d45
>
> Reported-by: syzbot <syzbot+1068f09c44d151250c33@xxxxxxxxxxxxxxxxxxxxxxxxx>
> Reported-by: syzbot <syzbot+e5344baa319c9a96edec@xxxxxxxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Reviewed-by: Michal Hocko <mhocko@xxxxxxxx>
Thanks!
> ---
> drivers/android/binder_alloc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
> index 42c672f1584e..cbe6aa77d50d 100644
> --- a/drivers/android/binder_alloc.c
> +++ b/drivers/android/binder_alloc.c
> @@ -947,7 +947,7 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
> trace_binder_unmap_user_end(alloc, index);
> }
> mmap_read_unlock(mm);
> - mmput(mm);
> + mmput_async(mm);
>
> trace_binder_unmap_kernel_start(alloc, index);
>
> --
> 2.18.4
--
Michal Hocko
SUSE Labs
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