Hi, tj,
On Fri, Aug 1, 2014 at 8:50 PM, Tejun Heo <t...@kernel.org> wrote:
> The *only* reason we have the warning at all is because the driver
> model wants to enforce that destruction is performed in the proper
> order and what you're doing is just circumventing the detection logic.
> We might as well just remove it. Please track down why the specific
> warning that you saw happened. We wanna learn about them and fix
> them.
The problem I met is in an old kernel, in sysfs_create_dir(), at thie line:
sysfs_create_dir()
if (kobj->parent)
parent = kobj->parent->sd;
I found kobj->parent is valid, so parent == kobj->parent->sd,
then it is passed into create_dir() function, in which it is dereferenced,
however the parent passed in is NULL, so a panic.
Apprently, there is a race, as my case is a test of fast removal and plugging
of a block device.
The race is that the kerfs_node(was sysfs_dirent) is disassociated with
parent kobject, but parent kobject is still alive, so we saw it.
And the commit 3a198886 ("sysfs: handle 'parent deleted before child added'")
add a parent NULLness check before calling into create_dir(), but I think this
isn't the real fix, it just narrow down the racy window.
Thanks,
Jianyu Zhan
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