Messages in this thread |  | | Date | Fri, 28 Sep 2001 02:11:15 +0200 | From | Andrea Arcangeli <> | Subject | Re: highmem deadlock fix [was Re: VM in 2.4.10(+tweaks) vs. 2.4.9-ac14/15(+stuff)] |
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On Thu, Sep 27, 2001 at 05:03:49PM -0700, Linus Torvalds wrote: > > On Fri, 28 Sep 2001, Andrea Arcangeli wrote: > > > > Moving clear_bit just above submit_bh will fix it (please Robert make > > this change before testing it), because if we block in submit_bh in the > > bounce, then we won't deadlock on ourself because of the pagehighmem > > check > > We won't block on _ourselves_, but we can block on _two_ people doing it,
If other people waits for us it's ok (if they waits it means they're not using GFP_NOIO and they're also not using GFP_NOHIGHIO).
We cannot wait on other two people doing it since they would be highmem pages and the pagehighmem check forbids that.
> and blocking on each others requests that are blocked waiting on a bounce > buffer. Both will have one locked buffer, both will be waiting for the > other person unlocking that buffer, and neither will ever make progress. > > You could clear that bit _after_ the bounce buffer allocation, I suspect.
I don't think it's necessary.
> But I also suspect that it doesn't matter much, and as I can imagine > similar problems with GFP_NOIO and loopback etc (do you see any reason why > loopback couldn't deadlock on waiting for itself?), I think the GFP_XXX > thing is the proper fix.
GFP_NOIO is a no brainer, it cannot go wrong see the other email.
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