process shared robust mutexes for tdb

[Stefan (metze) Metzmacher]

Hi,

here's the updated patchset that applies to master.

metze

Am 27.05.2013 14:19, schrieb Stefan (metze) Metzmacher:
> Hi,
> 
> here's the current patchset including configure checks and runtime
> checks for robust mutexes.
> 
> I think there's only one thing left that needs a bit more work,
> it's the error path handling in tdb_allrecord_upgrade().
> 
> For the non mutex case we do this:
> 
>      ret = tdb_brlock_retry(tdb, F_WRLCK, FREELIST_TOP,
>                             tdb->hash_size * 4,
>                             TDB_LOCK_WAIT|TDB_LOCK_PROBE);
> 
>      ret = tdb_brlock_retry(tdb, F_WRLCK, lock_offset(tdb->hash_size), 0,
>                             TDB_LOCK_WAIT|TDB_LOCK_PROBE);
> 
> while we locked the whole range with one call before.
> 
> The error path to cleanup the first lock if the 2nd fails does this
> currently:
> 
>         ret = tdb_brlock(tdb, F_RDLCK, FREELIST_TOP,
>                          tdb->hash_size * 4, TDB_LOCK_WAIT);
> 
> Wouldn't the following be the more correct way to undo the first lock?
> 
>      ret = tdb_brunlock(tdb, F_WRLCK, FREELIST_TOP, tdb->hash_size * 4)
> 
> instead of doing an additional read lock?
> 
> For the mutex case we'd also need to undo tdb_mutex_allrecord_upgrade().
> 
> This passes make test for me on an ubuntu 12.04 system with mutexes in use.
> (also with a hack to use mutexes whenever CLEAR_IF_FIRST is passed to
> tdb_open_ex()).
> 
> Note that older systems like SLES 10 or ubuntu 10.04 doesn't offer
> robust mutexes at runtime
> and our autobuild on sn-devel-104 (ubuntu 10.04) will not test mutexes
> in use,
> it'll silently fallback to fcntl() locks.
> 
> metze
> 
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