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SubjectRe: [PATCH v5 13/14] locks: skip deadlock detection on FL_FILE_PVT locks
[grr, gmail -- I didn't actually intend to send that.]

On Tue, Jan 14, 2014 at 1:24 PM, Andy Lutomirski <luto@amacapital.net> wrote:
> On Tue, Jan 14, 2014 at 1:19 PM, Frank Filz <ffilzlnx@mindspring.com> wrote:
>>> process 2 requests a write lock, gets -EDEADLK, unlocks and
>>> requests a new read lock. That request succeeds because there
>>> is no conflicting lock. (Note the lock manager had no
>>> opportunity to upgrade 1's lock here thanks to the conflict with
>>> 3's lock.)
>>
>> As I understand write lock priority, process 2 requesting a new read lock
>> would block, once there is a write lock waiter, no further read locks would
>> be granted that would conflict with that waiting write lock.
>
> ...which reminds me -- if anyone implements writer priority, please
> make it optional (either w/ a writer-priority-ignoring read lock or a
> non-priority-granting write lock). I have an application for which
> writer priority would be really annoying.
>
> Even better: Have read-lock-and-wait-for-pending-writers be an explicit new operation.
>
> (Writer priority a

Writer priority can introduce new deadlocks. Suppose that a reader
(holding a read lock) starts a subprocess that takes a new read lock
and waits for that subprocess. Throw an unrelated process in that
tries to take a write lock and you have an instant deadlock.

--Andy


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