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Update some comments

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This commit is contained in:
Gregory Nutt 2016-11-23 17:40:01 -06:00
parent 7dbc25b02b
commit 7bec4ffeec
1 changed files with 14 additions and 13 deletions
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27
sched/irq/irq_csection.c
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@ -112,31 +112,32 @@ static inline void irq_waitlock(int cpu)
while (up_testset(&g_cpu_irqlock) == SP_LOCKED)
{
/* The deadlock condition would occur if CPUn:
/* A deadlock condition would occur if CPUn:
*
* 1. Holds the g_cpu_irqlock, and
* 2. Is trying to interrupt CPUm
* 1. Holds the g_cpu_irqlock, and
* 2. Is trying to interrupt CPUm, but
* 3. CPUm is spinning trying acquaire the g_cpu_irqlock.
*
* The protocol for CPUn to pause CPUm is as follows
*
* 1. The up_cpu_pause() implementation on CPUn locks both
* g_cpu_wait[m] and g_cpu_paused[m]. CPUn then waits
* spinning on g_cpu_wait[m].
* 2. When CPUm receives the interrupt it (1) unlocks
* g_cpu_paused[m] and (2) locks g_cpu_wait[m]. The
* first unblocks CPUn and the second blocks CPUm in the
* interrupt handler.
* 1. The up_cpu_pause() implementation on CPUn locks both
* g_cpu_wait[m] and g_cpu_paused[m]. CPUn then waits
* spinning on g_cpu_wait[m].
* 2. When CPUm receives the interrupt it (1) unlocks
* g_cpu_paused[m] and (2) locks g_cpu_wait[m]. The
* first unblocks CPUn and the second blocks CPUm in the
* interrupt handler.
*
* The problem in the deadlock case is that CPUm cannot receive
* the interrupt because it is locked up spinning. He we break
* the interrupt because it is locked up spinning. Here we break
* the deadlock here be handling the pause interrupt request
* while waiting.
*/
if (up_cpu_pausereq(cpu))
{
/* Yes.. some CPU is requesting to pause us! Handle the
* pause interrupt now.
/* Yes.. some other CPU is requesting to pause this CPU! Handle
* the pause interrupt now.
*/
DEBUGVERIFY(up_cpu_paused(cpu));