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From: Ben Hutchings <b...@decadent.org.uk>
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On Wed, 2009-08-19 at 02:47 +0100, Ben Hutchings wrote:
[...]
> The kernel was spinning in process context, was interrupted by the SATA
> device, and its interrupt handler also started spinning.
>=20
> The BUG line is here:
>=20
> /* announce we're spinning */
> spinning =3D &__get_cpu_var(spinning);
> if (spinning->lock) {
> BUG_ON(spinning->lock =3D=3D lock);
> if(raw_irqs_disabled()) {
> BUG_ON(__get_cpu_var(spinning_bh).lock =3D=3D lock);
> spinning =3D &__get_cpu_var(spinning_irq);
> } else {
> -> BUG_ON(!in_softirq());
> spinning =3D &__get_cpu_var(spinning_bh);
> }
> BUG_ON(spinning->lock);
> }
> spinning->ticket =3D token;
> smp_wmb();
> spinning->lock =3D lock;
>=20
> This asserts that if we spin on a lock after interrupting another spin,
> and interrupts are enabled, we must be in a softirq.
>=20
> This seems bogus to me - in general, interrupts are enabled during
> interrupt handlers once their specific IRQ has been masked.
>=20
> I'll have a look at whether & how this code has changed upstream and in
> other forward-ported branches.
In the SLE 11.0 branch (downloaded from SUSE KOTD:
<ftp://ftp.suse.com/pub/projects/kernel/kotd/>) xen_spin_wait() allows
for arbitrarily nested spinlocks and has no such assertions.
The XCI tree
(<http://xenbits.xen.org/git-http/xenclient/linux-2.6.27.git> with patch
queue <http://xenbits.xen.org/git-http/xenclient/linux-2.6.27-pq.git>)
matches SLE 11.0.
This rather suggests that the assertions are wrong and we need to change
them.
Ben.
--=20
Ben Hutchings
The generation of random numbers is too important to be left to chance.
- Robert Coveyo=
u
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