2.2.1{3,4,5pre*} VM bug found

[Stephen C. Tweedie]

Hi,

On Tue, 25 Jan 2000 04:27:43 +0100 (CET), Rik van Riel
<riel en nl.linux.org> said:

> Sometimes a process with tsk->state != TASK_RUNNABLE
> calls __get_free_pages(). When we're (almost) out of
> memory, the process will wake up kswapd and try to
> free some memory itself.

> In 2.2.15pre4 or when the call to try_to_free_pages()
> generates disk I/O, the task will call schedule().
> Since the task state != TASK_RUNNABLE, schedule() will
> immedately remove it from the run queue ...

Shouldn't be a problem.  Anywhere that we stall in try_to_free_pages()
to wait for disk IO, we obviously have to set task->state to
TASK_UNINTERRUPTIBLE, as we're about to block.  If we do that as a
result of disk IO, then we have necessarily already scheduled a wakeup
event which will set the task state back to runnable.

So, the only risk is that the call to try_to_free_pages() has the
unexpected side effect of setting the task state to TASK_RUNNABLE.  That
isn't a problem: the only effect it will have on the caller is to make a
call schedule() return sooner than expected.  

--Stephen

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