Date: Wed, 4 Jul 2012 08:12:25 -0700
Subject: Re: Why can not processes switch in atomic context?
From: dhylands at gmail.com
To: buyit at live.cn
CC: mobile.parmenides at gmail.com; kernelnewbies at kernelnewbies.org

Hi,

On Wed, Jul 4, 2012 at 3:44 AM, ?? ? [off-list ref] wrote:

quoted

? 2012-7-3?22:26?"Parmenides" [off-list ref] ???

...snip...

quoted

quoted

1. For the spinlock case, it is easy to get if preemption is allowed
in critical section, the purpose of protection provided by spinlock
can not be achieved readily.

i think disable preemption in spinlock is not for safe, it is
For efficiency. Spinlock should exit as soon as possible.
If tank1 get spinlock and goto sleep for 100 seconds before
Release spinlock, task2 which requests the same spinlock
Should wait for 100 seconds, for this example, mutex should be used instead of spinlock.

Unless, of course, the interrupt that fired tried to acquire the
spinlock it preempted, in which case you would have deadlock, even on
an SMP system, if the same processor happened to be used for both.

 
yes, i think you are right, suppose task1 use spin_lock_irqsave() to get a spinlock, 
then call schedule() to sleep for a long time, the interrupt on this cpu core will be
enabled by kernel, and if there is an interrupt triggered on the same cpu and 
get the same spinlock, deadlock will happen.
 

  		 	   		  
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