Thomas Gleixner wrote:
On Sun, 2005-03-20 at 07:36 +0100, Manfred Spraul wrote:
cpu 1: acquire random networking spin_lock_bh()
cpu 2: read_lock(&tasklist_lock) from process context interrupt. softirq. within softirq: try to acquire the networking lock. * spins.
cpu 1: hardware interrupt within hw interrupt: signal delivery. tries to acquire tasklist_lock.
--> deadlock.
Signal delivery from hw interrupt context (interrupt is flagged SA_NODELAY) is not possible in RT preemption mode. The local_irq_save_nort() check in __cache_alloc will catch you.
That was just one random example. Another one would be :
drivers/chat/tty_io.c, __do_SAK() contains read_lock(&tasklist_lock); task_lock(p);
kernel/sys.c, sys_setrlimit contains task_lock(current->group_leader); read_lock(&tasklist_lock);
task_lock is a shorthand for spin_lock(&p->alloc_lock). If read_lock is a normal spinlock, then this is an A/B B/A deadlock.
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