Messages in this thread Patch in this message | | | Subject | Re: in_interrupt race | From | Robert Love <> | Date | 22 Apr 2002 15:02:53 -0400 |
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On Sat, 2002-04-20 at 06:27, Paul Mackerras wrote:
> Thus if we have CONFIG_SMP and CONFIG_PREEMPT, there is a small but > non-zero probability that in_interrupt() will give the wrong answer if > it is called with preemption enabled. If the process gets scheduled > from cpu A to cpu B between calling smp_processor_id() and evaluating > local_irq_count(cpu) or local_bh_count(), and cpu A then happens to be > in interrupt context at the point where the process resumes on cpu B, > then in_interrupt() will incorrectly return 1.
Looks like you are probably right ...
> One idea I had is to use a couple of bits in > current_thread_info()->flags to indicate whether local_irq_count and > local_bh_count are non-zero for the current cpu. These bits could be > tested safely without having to disable preemption.
For now we can just do this,
--- linux-2.5.8/include/asm-i386/hardirq.h Sun Apr 14 15:18:55 2002 +++ linux/include/asm-i386/hardirq.h Mon Apr 22 14:56:29 2002 @@ -21,8 +21,10 @@ * Are we in an interrupt context? Either doing bottom half * or hardware interrupt processing? */ -#define in_interrupt() ({ int __cpu = smp_processor_id(); \ - (local_irq_count(__cpu) + local_bh_count(__cpu) != 0); }) +#define in_interrupt() ({ int __cpu; preempt_disable(); \ + __cpu = smp_processor_id(); \ + (local_irq_count(__cpu) + local_bh_count(__cpu) != 0); \ + preempt_enable(); }) #define in_irq() (local_irq_count(smp_processor_id()) != 0) Or perhaps leave the code as-is but make the rule preemption needs to be disabled before calling (either implicitly or explicitly). I.e., via a call to preempt_disable or because interrupts are disabled, a lock is held, etc ...
> In fact almost all uses of local_irq_count() and local_bh_count() are > for the current cpu; the exceptions are the irqs_running() function > and some debug printks. Maybe the irq and bh counters themselves > could be put into the thread_info struct, if irqs_running could be > implemented another way.
One thing Linus, DaveM, and I discussed a while back was actually getting rid of the irq and bh counts completely and folding them into preempt_count. I am interested in this...
Robert Love
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