On Tue, Dec 20, 2005 at 06:34:20AM -0800, Suleiman Souhlal wrote: > Hello Luigi, > > Luigi Rizzo wrote: > > as in the subject... i see that td->td_critnest (used to determine > > whether a thread can be preempted or not) is manipulated using > > plain ++ or -- instruction instead of the atomic_add_int(). > > This should be fine as it only gets modified by the current thread. If > an interrupt comes while we are decreasing td_critnest back to 0, then > we just don't get preempted immediately, but at the end of our quantum, > or when someone else tries to preempt us, whichever comes first, which > should be totally harmless. i think that there are still some potential race conditions if the variable is read from another processor to make a decision based on its value. My understanding is that when critical_enter() returns, everything in the system should read td->td_critnest >= 1, which may not be guaranteed by the current implementation (which doesn't have smp locks). There might be similar issues in the 1->0 transition. cheers luigiReceived on Tue Dec 20 2005 - 15:16:19 UTC
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