From: Anton Ivanov <antiv...@cisco.com>
Occasionally, under very heavy load inside UML, on host
or both one of the processes in UML will remain in D state
or will fail to reap a child which will sit in Z state.
This is very difficult to reproduce with stock UML because
the lseek()/read()|write()|fsync() in the ubd driver will
cause a constant "trickle" of memory synchronization regardless
of what UML is doing. It is possible though (3-4 hours of
loadavg >6 stress load with low memory can trigger it).
If lseek()/read()|write() are replaced with its equivalent
pread()|pwrite() the original bug becomes much easier to
reproduce. It now takes 5-10 minutes of heavy IO to cause it.
This fix seems to cure it. I am not sure if this is the best
place to invoke a memory barrier, this one works.
Signed-off-by: Anton Ivanov <antiv...@cisco.com>
---
This version takes into account the fact that uml picks up the
correct define out of arch/x86/um/barrier.h so no need to invoke it
directly - noted by Richard Weinberger
I still do not know if this is the correct location to hit it with a
mb(). This one seems to cure it.
arch/um/kernel/exec.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/um/kernel/exec.c b/arch/um/kernel/exec.c
index 0d7103c..86b1dc1 100644
--- a/arch/um/kernel/exec.c
+++ b/arch/um/kernel/exec.c
@@ -27,6 +27,7 @@ void flush_thread(void)
ret = unmap(¤t->mm->context.id, 0, STUB_START, 0, &data);
ret = ret || unmap(¤t->mm->context.id, STUB_END,
host_task_size - STUB_END, 1, &data);
+ mb();
if (ret) {
printk(KERN_ERR "flush_thread - clearing address space failed, "
"err = %d\n", ret);
--
1.7.10.4
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