Re: [PATCH] fs: synchronize_rcu when unregister_filesystem successnot failure

[Marco Stornelli]

Il 14/04/2011 17:52, Linus Torvalds ha scritto:
> On Thu, Apr 14, 2011 at 8:41 AM, Milton Miller<miltonm@xxxxxxx>  wrote:
> > While checking unregister_filesystem for saftey vs extra calls for
> > "ext4: register ext2 and ext3 alias after ext4" I realized that
> > the synchronize_rcu() was called on the error path but not on
> > the success path.
>
> Good catch.
>
> I think this is the bug that then caused us to do commit d863b50ab013
> ("vfs: call rcu_barrier after ->kill_sb()")
>
> That said, that commit says that "synchronize_rcu()" isn't enough, and
> uses rcu_barrier().
>
> Which _should_ mean that there are no actual users that care about RCU
> events by the time you actually hit "unregister_filesystem()".
>
> So I think your patch is correct, but won't actually matter. But maybe
> I'm missing something.
>
> > Should we call it in both?
>
> No, I think the success path is the one that would matter.
>
> Comments?

If I well remember the rcu_barrier was needed for the fs module 
unloading problem. In that case synchronize_rcu() wasn't enough. That 
said, I agree with you, it won't have any impact.

Marco
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