Re: [RFC] How to fix an async scan - rmmod race?

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On 04/06/12 15:20, James Bottomley wrote:

> On Fri, 2012-04-06 at 11:54 +0200, Tomas Henzl wrote:
>> I like this idea(try_module_get) it is easy/elegant and it is used in scsi_rescan_device,
>> but a scan can take a lot of time and during that time the driver couldn't be removed.
>> When a flag in scsi_remove_host is set then the scan can be cancelled, if the user 
>> rmmods the driver.
> This is my preferred solution too.  The rule for async stuff is either
> cancel or wait and since we can't cancel, we need to ensure the wait by
> holding the module until the async event has finished.
> Since the whole of the host scan must complete, we need to hold the
> module across that, but I bet we also need to hold it across user
> triggered target scans as well.

As far as I can see the queuecommand call in scsi_dispatch_cmd() can
race with module removal - that call can be triggered while the host
template is being unloaded. I'm not sure though what the best approach
is to fix that race.

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