On Mon, Feb 16, 2009 at 09:29:00AM +0800, Li Zefan wrote:
> >> struct mnt_writer *cpu_writer = &per_cpu(mnt_writers, cpu);
> >> spin_lock(&cpu_writer->lock);
> >> if (cpu_writer->mnt != mnt) {
> >> spin_unlock(&cpu_writer->lock);
> >> continue;
> >> }
> >> prevents the problem, OK?
> >>
> >
> > Sure, I'll try. :)
> >
>
> Not a single warning for the whole weekend, so I think above change works.
OK... So here's what we really want:
* we know that nobody will set cpu_writer->mnt to mnt from now on
* all changes to that sucker are done under cpu_writer->lock
* we want the laziest equivalent of
spin_lock(&cpu_writer->lock);
if (likely(cpu_writer->mnt != mnt)) {
spin_unlock(&cpu_writer->lock);
continue;
}
/* do stuff */
that would make sure we won't miss earlier setting of ->mnt done by another
CPU.
Anyway, for now (HEAD and all -stable starting with 2.6.26) we want this:
--- fs/namespace.c 2009-01-25 21:45:31.000000000 -0500
+++ fs/namespace.c 2009-02-15 21:31:14.000000000 -0500
@@ -614,9 +614,11 @@
*/
for_each_possible_cpu(cpu) {
struct mnt_writer *cpu_writer = &per_cpu(mnt_writers, cpu);
- if (cpu_writer->mnt != mnt)
- continue;
spin_lock(&cpu_writer->lock);
+ if (cpu_writer->mnt != mnt) {
+ spin_unlock(&cpu_writer->lock);
+ continue;
+ }
atomic_add(cpu_writer->count, &mnt->__mnt_writers);
cpu_writer->count = 0;
/*
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