no more recursive locks

wakeup1() assumes you hold proc_table_lock
sleep(chan, lock) provides atomic sleep-and-release to wait for condition
ugly code in swtch/scheduler to implement new sleep
fix lots of bugs in pipes, wait, and exit
fix bugs if timer interrupt goes off in schedule()
console locks per line, not per byte

Notes

@@ -126,3 +126,26 @@ nasty hack to allow locks before first process,
 
 race between release and sleep in sys_wait()
 race between sys_exit waking up parent and setting state=ZOMBIE
+race in pipe code when full/empty
+
+lock order
+  per-pipe lock
+  proc_table_lock fd_table_lock kalloc_lock
+  console_lock
+
+condition variable + mutex that protects it
+  proc * (for wait()), proc_table_lock
+  pipe structure, pipe lock
+
+systematic way to test sleep races?
+  print something at the start of sleep?
+
+do you have to be holding the mutex in order to call wakeup()?
+
+should lock around printf, not putc
+
+device interrupts don't clear FL_IF
+  so a recursive timer interrupt is possible
+
+the sleep/swtch/schedule code that holds over a lock is ugly
+