On Sat, 11 Nov 2017 16:08:34 +0100 Boris Brezillon boris.brezillon@free-electrons.com wrote:

Commit e8e3edb95ce6 ("mtd: create per-device and module-scope debugfs entries") tried to make MTD related debugfs stuff consistent across the MTD framework by creating a root <debugfs>/mtd/ directory containing one directory per MTD device.

The problem is that, by default, the MTD layer only registers the master device if no partitions are defined for this master. This behavior breaks all drivers that expect mtd->dbg.dfs_dir to be filled correctly after calling mtd_device_register() in order to add their own debugfs entries.

The only way we can force all MTD masters to be registered no matter if they expose partitions or not is by enabling the CONFIG_MTD_PARTITIONED_MASTER option.

In such situations, there's no other solution but to accept skipping debugfs initialization when dbg.dfs_dir is invalid, and when this happens, inform the user that he should consider enabling CONFIG_MTD_PARTITIONED_MASTER.

Fixes: e8e3edb95ce6 ("mtd: create per-device and module-scope debugfs entries") Cc: stable@vger.kernel.org Cc: Mario J. Rugiero mrugiero@gmail.com

Forgot to add:

Reported-by: Richard Weinberger richard@nod.at

Also forgot to mention that this patch is supposed to replace patches "mtd: Make sure MTD objects always have a valid debugfs dir" and "mtd: mtdpart: Create a symlink to the master debugfs dir". Indeed, after discussing it with Brian, I realized those patches were going in the wrong direction: we should encourage people to move to MTD_PARTITIONED_MASTER instead of constantly fixing this kind of bugs (one other example in mind I have is that mtd->dev is not suitable for any devm_xxx() methods because the underlying may or may not be registered).

Regards,

Boris

Signed-off-by: Boris Brezillon boris.brezillon@free-electrons.com

drivers/mtd/devices/docg3.c | 7 ++++++- drivers/mtd/nand/nandsim.c | 13 +++++++++---- 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/mtd/devices/docg3.c b/drivers/mtd/devices/docg3.c index 84b16133554b..0806f72102c0 100644 --- a/drivers/mtd/devices/docg3.c +++ b/drivers/mtd/devices/docg3.c @@ -1814,8 +1814,13 @@ static void __init doc_dbg_register(struct mtd_info *floor) struct dentry *root = floor->dbg.dfs_dir; struct docg3 *docg3 = floor->priv;

• if (IS_ERR_OR_NULL(root))

• if (IS_ERR_OR_NULL(root)) {

• if (IS_ENABLED(CONFIG_DEBUG_FS) &&
  

•     !IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER))
  

• 	dev_warn(floor->dev.parent,
  

• 		 "CONFIG_MTD_PARTITIONED_MASTER must be enabled to expose debugfs stuff\n");
  

  return;
• }

debugfs_create_file("docg3_flashcontrol", S_IRUSR, root, docg3, &flashcontrol_fops); diff --git a/drivers/mtd/nand/nandsim.c b/drivers/mtd/nand/nandsim.c index 246b4393118e..44322a363ba5 100644 --- a/drivers/mtd/nand/nandsim.c +++ b/drivers/mtd/nand/nandsim.c @@ -520,11 +520,16 @@ static int nandsim_debugfs_create(struct nandsim *dev) struct dentry *root = nsmtd->dbg.dfs_dir; struct dentry *dent;

• if (!IS_ENABLED(CONFIG_DEBUG_FS))

• /*

• * Just skip debugfs initialization when the debugfs directory is
  

• * missing.
  

• */
  

• if (IS_ERR_OR_NULL(root)) {

• if (IS_ENABLED(CONFIG_DEBUG_FS) &&
  

•     !IS_ENABLED(CONFIG_MTD_PARTITIONED_MASTER))
  

• 	NS_WARN("CONFIG_MTD_PARTITIONED_MASTER must be enabled to expose debugfs stuff\n");
  

  return 0;

• if (IS_ERR_OR_NULL(root))

• return -1;
  

• }

dent = debugfs_create_file("nandsim_wear_report", S_IRUSR, root, dev, &dfs_fops);