linux-kernel - Re: Spinlocks waiting with interrupts disabled / preempt disabled.

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Message-ID: <Pine.LNX.4.64.0805071022230.3173@schroedinger.engr.sgi.com>
Date:	Wed, 7 May 2008 10:24:18 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Ingo Molnar <mingo@...e.hu>
cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: Spinlocks waiting with interrupts disabled / preempt disabled.

Looks like an issue with old code in SLES10. Upstream has:

/*
 * If lockdep is enabled then we use the non-preemption spin-ops
 * even on CONFIG_PREEMPT, because lockdep assumes that interrupts are
 * not re-enabled during lock-acquire (which the preempt-spin-ops do):
 */
#if !defined(CONFIG_GENERIC_LOCKBREAK) || defined(CONFIG_DEBUG_LOCK_ALLOC)

.. followed by function definitions that disable interrupts before 
spinning.

#else

...

unsigned long __lockfunc _##op##_lock_irqsave(locktype##_t *lock)       \
{                                                                       \
        unsigned long flags;                                            \
                                                                        \
        for (;;) {                                                      \
                preempt_disable();                                      \
                local_irq_save(flags);                                  \
                if (likely(_raw_##op##_trylock(lock)))                  \
                        break;                                          \
                local_irq_restore(flags);                               \
                preempt_enable();                                       \
                                                                        \
                if (!(lock)->break_lock)                                \
                        (lock)->break_lock = 1;                         \
                while (!op##_can_lock(lock) && (lock)->break_lock)      \
                        _raw_##op##_relax(&lock->raw_lock);             \
        }                                                               \
        (lock)->break_lock = 0;                                         \
        return flags;                                                   \
}                                                                       \
                                       
So this is only an issue if certain debug options are enabled.

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