Re: sysfs_bin_mmap lockdep trace.

[Al Viro <viro@ZenIV.linux.org.uk>]

On Wed, Nov 13, 2013 at 01:45:38PM -0500, Dave Jones wrote:
> Al, is this one also known ? Also seen on v3.12-7033-g42a2d923cc34

Umm...  I've seen something like that reported after sysfs merge went in
(right after 3.12), but I hadn't looked into details.

> -> #3 (&mm->mmap_sem){++++++}:

	[sr_block_ioctl() grabs sr_mutex and does copy_from_user() under it]

> -> #2 (sr_mutex){+.+.+.}:
	[sr_block_open() grabs sr_mutex under ->bd_mutex]

> -> #1 (&bdev->bd_mutex){+.+.+.}:
	[sysfs_blk_trace_attr_show() grabs ->bd_mutex and is called under
sysfs_open_file ->mutex]

> -> #0 (&of->mutex){+.+.+.}:
	[sysfs_open_file ->mutex is grabbed by ->mmap()]

Cute...  AFAICS, it came from "sysfs: copy bin mmap support from fs/sysfs/bin.c
to fs/sysfs/file.c".  The first impression is that sysfs_bin_mmap() is
checking for battr->mmap too late, but I'm not sure whether we need of->mutex
to stabilize it...  Tejun, any comments?