On Wednesday 21 September 2005 21:49, Andrew Morton wrote:
> "Paolo 'Blaisorblade' Giarrusso" <[email protected]> wrote:
> > From: Paolo 'Blaisorblade' Giarrusso <[email protected]>
> The in_atomic() test in x86's do_page_fault() is in fact a message passed
> into it from filemap.c's kmap_atomic().
Ok, this can be ok, but:
> It has accidental side-effects,
> such as making copy_to_user() fail if inside spinlocks when
> CONFIG_PREEMPT=y.
Sorry, but should it ever succeed inside spinlocks? I mean, should it ever
call down() inside spinlocks? (We never do down_trylock, and ever if we did
the x86 trick, that wouldn't make the whole thing safe at all - they still
take the spinlock and potentially sleep. And it's legal only if no spinlock
is held).
Even if spinlocks don't always trigger in_atomic() - which means that we'd
need to have a better fix for this.
(Btw, I took the above reasoning from something said, as an aside, on LWN.net
kernel page, about the FUTEX deadlock on mm->mmap_sem of ~ 2.6.8 - yes, it
wasn't the full truth, but not totally dumb).
> So I think this change is only needed if UML implements kmap_atomic, as in
> arch/i386/mm/highmem.c, which it surely does not do?
NACK, see above.
--
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade
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