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(-)
--- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -987,7 +987,7 @@ enum lru_status binder_alloc_free_page(s trace_binder_unmap_user_end(alloc, index); } up_read(&mm->mmap_sem); - mmput(mm); + mmput_async(mm);
trace_binder_unmap_kernel_start(alloc, index);