From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> commit f867c771f98891841c217fa8459244ed0dd28921 upstream. 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=bc9e7303f537c41b2b0cc2dfcea3fc42964c2d4... Reported-by: syzbot <syzbot+1068f09c44d151250c33@syzkaller.appspotmail.com> Reported-by: syzbot <syzbot+e5344baa319c9a96edec@syzkaller.appspotmail.com> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Reviewed-by: Michal Hocko <mhocko@suse.com> Acked-by: Todd Kjos <tkjos@google.com> Acked-by: Christian Brauner <christian.brauner@ubuntu.com> Cc: stable <stable@vger.kernel.org> Link: https://lore.kernel.org/r/4ba9adb2-43f5-2de0-22de-f6075c1fab50@i-love.sakura... Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- 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 6e5e6fb7e4c9..3371b986e3b4 100644 --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -987,7 +987,7 @@ enum lru_status binder_alloc_free_page(struct list_head *item, trace_binder_unmap_user_end(alloc, index); } up_read(&mm->mmap_sem); - mmput(mm); + mmput_async(mm); trace_binder_unmap_kernel_start(alloc, index); -- 2.25.1