On Tue, Nov 21, 2017 at 2:42 PM, Adrian Hunter [off-list ref] wrote:

The card is not necessarily being removed, but the debugfs files must be
removed when the driver is removed, otherwise they will continue to exist
after unbinding the card from the driver. e.g.

  # echo "mmc1:0001" > /sys/bus/mmc/drivers/mmcblk/unbind
  # cat /sys/kernel/debug/mmc1/mmc1\:0001/ext_csd
  [  173.634584] BUG: unable to handle kernel NULL pointer dereference at 0000000000000050
  [  173.643356] IP: mmc_ext_csd_open+0x5e/0x170

A complication is that the debugfs_root may have already been removed, so
check for that too.

Fixes: 627c3ccfb46a ("mmc: debugfs: Move block debugfs into block module")
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>

Reviewed-by: Linus Walleij <redacted>

I was assuming debugfs would always be removed from debugfs.c
using debugfs_remove_recursive(card->debugfs_root) but that
doesn't work for this case where we bin/unbind the block layer
interactively, sorry for missing it :(

Ulf: I think this can go in as an *early* fix as well, say after -rc1.

Yours,
Linus Walleij