On Wed, Dec 1, 2010 at 3:36 PM, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Wed, 1 Dec 2010 15:31:11 -0800
> Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>>
>> Ergo: vmscan has a locked page leads to the filesystem being
>> guaranteed to not be unmounted. And that, in turn, guarantees that
>> the module won't be unloaded until the machine has gone through an
>> idle cycle.
>
> The page isn't attached to the address_space any more:
Did you even read the email?
Here, let me quote the important parts:
"module won't be unloaded until the machine has gone through an idle cycle"
"This is pretty much how all the module races are handled. Doing module
ref-counts per page (or per packet in flight for things like
networking) would be prohibitively expensive."
IOW, the whole "stop_machine()" part is fundamental. That whole
"module unload won't happen until we've gone through an idle cycle" is
EXACTLY why we don't need to have the page attached or ref-counted -
we're still safe.
Linus
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