How to unload a module? (Was: rqdm: bad usage of dm_get/dm_put)
On Thu, 25 Feb 2010, Kiyoshi Ueda wrote:
> Hi Mikulas,
> On 02/25/2010 07:33 AM +0900, Mikulas Patocka wrote:
> >> Indeed, we shouldn't use the current dm_put() in any interrupt-context.
> >> But the "mapped_device" can disappear in request-based dm while there
> >> is a request after all bios complete, so I used dm_get()/dm_put() there.
> >> I'll consider another way to prevent the problem without dm_get()/dm_put().
> >> E.g. wait for request completion in dm_put() instead.
> > How can a request-in-progress exists when all the bios complete and the
> > device is closed?
> In the current request-based dm, the device opener can remove
> the mapped_device while the last request is still completing,
> because bios in the last request complete first and then the device
> opener can remove the mapped_device before the last request completes:
> CPU0 CPU1
> ================================================== ====================
> bio_endio(clone_bio) == end_clone_bio
> <<I/O completed>>
> <<Free md>>
> So we need a mechanism to defer the md deletion until the last request
> Kiyoshi Ueda
Good point ... but I think this problem may happen even in normal
non-request based dm.
I don't know what to do with it.
If one thread does:
and another thread does:
- close the device
- remove the device
- unload module
- then the first thread, after bio_endio, executes non-existing
instructions from unloaded module.
Any ideas, how is it solved or how it should be solved?
Module unloading does stop_machine, but AFAIK it waits for all CPUs to
exit non-preemtable sections, it doesn't wait for the code to get out of
disk request routine...
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