Deadlock in nullfs/zfs somewhere

[Andriy Gapon]

on 21/07/2013 10:11 Konstantin Belousov said the following:
> On Fri, Jul 19, 2013 at 10:33:11PM +0300, Andriy Gapon wrote:
>> on 19/07/2013 21:42 Konstantin Belousov said the following:
>>> Then, you cannot use VFS suspension.  Or, in other words, you are
>>> directed to abuse the VFS interface.  I assure you that any changes to
>>> the interface would not take into account such abuse and probably break
>>> your hack.
>> 
>> So what would be your recommendation about this problem? Should we add
>> another flavor of VFS suspension? The one that would mean "all external
>> accesses to this fs must be put on hold", but would not imply "this fs is
>> frozen".
> 
> Suspension is very complicated as it is. Adding another flavour would 
> multiply the current mess^H^H^H^H collection of subtleties. IMO, the best
> route is to use the KPI properly, i.e. adding the vn_start_write() braces
> around the top-level entries in the mutating code paths.
> 

So how will this help with doing a rollback in the thread that does the following?

vfs_write_suspend
zfs rollback
vfs_write_resume

-- 
Andriy Gapon