[uml-devel] Re: [PATCH 3/7] uml: make copy_*_user atomic

[Blaisorblade <blaisorblade@yahoo.it>]

On Sunday 30 April 2006 16:16, Paolo 'Blaisorblade' Giarrusso wrote:
> From: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
>
> Make __copy_*_user_inatomic really atomic to avoid "Sleeping function
> called in atomic context" warnings, especially from futex code.
>
> This is made by adding another kmap_atomic slot and making copy_*_user_skas
> use kmap_atomic; also copy_*_user() becomes atomic, but that's true and is
> not a problem for i386 (and we can always add might_sleep there as done
> elsewhere). For TT mode kmap is not used, so there's no need for this.
>
> I've had to use another slot since both KM_USER0 and KM_USER1 are used
> elsewhere and could cause conflicts. Till now we reused the kmap_atomic
> slot list from the subarch, but that's not needed as that list must contain
> the common ones (used by generic code) + the ones used in architecture
> specific code (and Uml till now used none); so I've taken the i386 one
> after comparing it with ones from other archs, and added KM_UML_USERCOPY.

> Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>

Ok, I didn't want indeed to send this one _for merging_, even if I consider it 
correct and it indeed fixes the warnings; additionally, since HIGHMEM support 
is not very used (it's slow and less tested), there shouldn't be problems 
anyway.

Please keep it in -mm however, it should be ok and there it could get more 
exposure - and this is about interaction with the core kernel so it could get 
valid review from people outside UML.

Jeff, give a look to this one please. You need CONFIG_DEBUG_SPINLOCK_SLEEP and 
a futex user (for instance starting threaded apache inside the guest) to 
trigger the warnings.
-- 
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
Chiacchiera con i tuoi amici in tempo reale! 
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