On Fri, Jul 05, 2013 at 09:57:11PM +0530, Preeti U Murthy wrote: > Elaborate on when deadlocks can occur when a call is made to > smp_call_function_single() and its friends. This avoids ambiguity about > when to use these calls. > > Signed-off-by: Preeti U Murthy <pre...@linux.vnet.ibm.com> > Cc: Peter Zijlstra <a.p.zijls...@chello.nl> > Cc: Ingo Molnar <mi...@elte.hu> > Cc: Xiao Guangrong <xiaoguangr...@cn.fujitsu.com> > Cc: srivatsa.b...@linux.vnet.ibm.com > Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com> > Cc: Steven Rostedt <rost...@goodmis.org> > Cc: Rusty Russell <ru...@rustcorp.com.au > --- > > kernel/smp.c | 46 ++++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 44 insertions(+), 2 deletions(-) > > diff --git a/kernel/smp.c b/kernel/smp.c > index 89be6e6..b6981ae 100644 > --- a/kernel/smp.c > +++ b/kernel/smp.c > @@ -230,7 +230,23 @@ int smp_call_function_single(int cpu, smp_call_func_t > func, void *info, > this_cpu = get_cpu(); > > /* > - * Can deadlock when called with interrupts disabled. > + * Can deadlock when called with interrupts disabled under two > + * different circumstances depending on the wait parameter. > + * > + * 1. wait = 1: Two CPUs execute smp_call_function_single(), send an > + * IPI to each other, and wait for func to finish on each other. > + * Since they are interrupt disabled, neither receives this IPI, > + * nor do they proceed forward,as they wait for each other to complete > + * execution of func. > + *
Yes, we should avoid this situation, but I am not sure whether this is the meaning of "deadlock" in the original comment. > + * 2. wait = 0: This function could be called from an interrupt > + * context, and can get blocked on the csd_lock(csd) below in > + * "non wait cases". > + * This is because the percpu copy of csd of this_cpu is used > + * in non wait cases. Under such circumstances, if the previous caller > + * of this function who got preempted by this interrupt has already > taken > + * the lock under non wait condition, it will result in deadlock. > + * No, it will not cause deadlock, it is not mutex lock, it is busy wait, so when the CSD_FLAG_LOCK be cleared, the code will go on running. After stare into the kernel/smp.c, I can't catch what the exactly meaning of the "DeadLock" in the original comment also. I hope someone can clarify it. Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
