linux-kernel - CONFIG_VMAP_STACK, on-stack struct, and wake_up

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Date:   Wed, 26 Oct 2016 14:51:57 +0200
From:   Andreas Gruenbacher <agruenba@...hat.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Bob Peterson <rpeterso@...hat.com>,
        Steven Whitehouse <swhiteho@...hat.com>
Subject: CONFIG_VMAP_STACK, on-stack struct, and wake_up_bit

Hi,

CONFIG_VMAP_STACK has broken gfs2 and I'm trying to figure out what's
going on. What I'm seeing is the following: on a fresh gfs2 filesystem
created with:

  mkfs.gfs2 -p lock_nolock $DEVICE

I get the following BUG with 4.9-rc2, CONFIG_VMAP_STACK and
CONFIG_DEBUG_VIRTUAL turned on:

  kernel BUG at arch/x86/mm/physaddr.c:26!

Stack of kernel thread:

  __phys_addr(x)
  bit_waitqueue(word, bit)
  wake_up_bit(word = &gh->gh_iflags, bit = HIF_WAIT)
  gfs2_holder_wake(gh)

The gh here is on the stack of another kernel thread:

  static int fill_super(struct super_block *sb, struct gfs2_args
*args, int silent)
  {
    struct gfs2_holder mount_gh;
  }

Which is waiting on the bit with:

  wait_on_bit(&gh->gh_iflags, HIF_WAIT, TASK_UNINTERRUPTIBLE)

Is accessing a struct on another kernel thread's stack no longer working?

Thanks,
Andreas