On Fri, Aug 21, 2015 at 07:42:30PM +0200, Oleg Nesterov wrote:
> Hello,
>
> Now that sb->s_writers was changed to use percpu_rw_semaphore let me
> send v2.
>
> Changes:
>
> - whitespace fix in 1/8.
>
> - remove EXPORT_SYMBOL() in 3/8, currently rcu_sync has no
> modular users.
>
> - 5/8 is new. This ugly hack pairs with another one:
> "shift percpu_counter_destroy() into destroy_super_work()"
>
> https://git.kernel.org/cgit/linux/kernel/git/viro/vfs.git/commit/?h=for-next&id=853b39a7c82826b8413048feec7bf08e98ce7a84
> They both will be reverted later.
>
> The problem is that we have 2 series routed via different
> trees, RCU and VFS. We need this hack to ensure that this
> series won't break alloc_super() which currently assumes that
> destroy_super()->percpu_free_rwsem() is safe after kzalloc().
> This way these 2 series do not depend on each other, we can
> test/change/revert/etc them independently.
>
> We will add rcu_sync_dtor() into deactivate_locked_super()
> later and revert both hacks.
> Oleg.
Queued for testing, thank you, Oleg!
Right now, this is mostly relying on 0day and -next testing. Any thoughts
for a useful torture test for this? One approach would be to treat it
like a reader-writer lock. Other thoughts?
Thanx, Paul
> include/linux/percpu-rwsem.h | 3 +-
> include/linux/rcusync.h | 56 +++++++++++++++
> kernel/locking/percpu-rwsem.c | 85 ++++++++---------------
> kernel/rcu/Makefile | 2 +-
> kernel/rcu/sync.c | 151
> +++++++++++++++++++++++++++++++++++++++++
> 5 files changed, 240 insertions(+), 57 deletions(-)
>
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