Using the PowerPC P2040 (e500mc) CPU, soft lockups can occasionally be seen in smp_call_function_many_cond(). The conclusion is that this CPU does not process the doorbell interrupt while in a data-storage (MMU) exception. If more than one CPU in a multi core environment is calling this function at the same time, it is possible for a deadlock to occur.
The fix for this is to call flush_smp_call_function_queue() before waiting for responses from other CPUs. If there is something in the queue, this is a good time to process it before busy-waiting on other CPUs. On other architectures this call will quickly do nothing, as the queue will be empty. Signed-off-by: Mark Tomlinson <[email protected]> --- kernel/smp.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/smp.c b/kernel/smp.c index a0bb56bd8dda..3c4467654ab0 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -884,6 +884,8 @@ static void smp_call_function_many_cond(const struct cpumask *mask, local_irq_restore(flags); } + flush_smp_call_function_queue(); + if (run_remote && wait) { for_each_cpu(cpu, cfd->cpumask) { call_single_data_t *csd; -- 2.54.0
