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SMP: Fix yet another potential deadlock

This commit is contained in:
Gregory Nutt 2016-11-25 23:04:27 -06:00
parent d6a3aab0b4
commit a0e1af2614
1 changed files with 70 additions and 5 deletions
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75
sched/irq/irq_csection.c
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@ -110,13 +110,13 @@ static inline void irq_waitlock(int cpu)
* for the deadlock condition.
*/
while (up_testset(&g_cpu_irqlock) == SP_LOCKED)
while (spin_trylock(&g_cpu_irqlock) == SP_LOCKED)
{
/* A deadlock condition would occur if CPUn:
*
* 1. Holds the g_cpu_irqlock, and
* 2. Is trying to interrupt CPUm, but
* 3. CPUm is spinning trying acquaire the g_cpu_irqlock.
* 3. CPUm is spinning trying acquire the g_cpu_irqlock.
*
* The protocol for CPUn to pause CPUm is as follows
*
@ -152,6 +152,57 @@ static inline void irq_waitlock(int cpu)
}
#endif
/****************************************************************************
* Name: task_waitlock
*
* Description:
* Spin to get g_irq_waitlock, handling a known deadlock condition:
*
* Suppose this situation:
*
* - CPUn enters a critical section and has the g_cpu_irqlock spinlock.
* - CPUn causes a task to become ready to run and scheduler selects
* CPUm. CPUm is requested to pause.
* - But CPUm is in a normal task and is also attempting to enter a
* critical section. So it is also spinning to get g_cpu_irqlock
* with interrupts disabled and cannot respond to the pause request,
* causing the deadlock.
*
* This function detects this deadlock condition while spinning with \
* interrupts disabled.
*
****************************************************************************/
#ifdef CONFIG_SMP
static inline bool task_waitlock(int cpu)
{
/* Duplicate the spin_lock() logic from spinlock.c, but adding the check
* for the deadlock condition.
*/
while (spin_trylock(&g_cpu_irqlock) == SP_LOCKED)
{
/* Is a pause request pending? */
if (up_cpu_pausereq(cpu))
{
/* Yes.. some other CPU is requesting to pause this CPU!
* Abort the wait and return false.
*/
return false;
}
SP_DSB();
}
/* We have g_cpu_irqlock! */
SP_DMB();
return true;
}
#endif
/****************************************************************************
* Public Functions
****************************************************************************/
@ -185,6 +236,8 @@ irqstate_t enter_critical_section(void)
* the local CPU.
*/
try_again:
ret = up_irq_save();
/* Verify that the system has sufficiently initialized so that the task
@ -218,14 +271,14 @@ irqstate_t enter_critical_section(void)
*
* g_cpu_irqlock = SP_LOCKED.
* g_cpu_nestcount = 0
* The bit in g_cpu_irqset for this CPU hould be zero
* The bit in g_cpu_irqset for this CPU should be zero
*
* 4. An extension of 3 is that we may be re-entered numerous
* times from the same interrupt handler. In that case:
*
* g_cpu_irqlock = SP_LOCKED.
* g_cpu_nestcount > 0
* The bit in g_cpu_irqset for this CPU hould be zero
* The bit in g_cpu_irqset for this CPU should be zero
*
* NOTE: However, the interrupt entry conditions can change due
* to previous processing by the interrupt handler that may
@ -305,7 +358,19 @@ irqstate_t enter_critical_section(void)
cpu = this_cpu();
DEBUGASSERT((g_cpu_irqset & (1 << cpu)) == 0);
spin_lock(&g_cpu_irqlock);
if (!task_waitlock(cpu))
{
/* We are in a potential deadlock condition due to a
* pending pause request interrupt. Re-enable interrupts
* on this CPU and try again. Briefly re-enabling
* interrupts should be sufficient to permit processing
* the pending pause request.
*/
up_irq_restore(ret);
goto try_again;
}
/* The set the lock count to 1.
*