Messages in this thread | | | Subject | Re: [PATCH 000 of 4] Introduction | From | Peter Zijlstra <> | Date | Wed, 11 Oct 2006 10:44:36 +0200 |
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On Wed, 2006-10-11 at 16:09 +1000, NeilBrown wrote: > Following 4 patches address issues with lockdep, particularly around bd_mutex. > > They are against 2.6.18-mm3 and do *not* apply against -linus as -mm already has > some changes to the handling of bd_mutex nesting. 2-4 probably apply on top of -linus plus > -mm/broken-out/remove-the-old-bd_mutex-lockdep-annotation.patch > > I believe they are probably ok for 2.6.19. > > The core issue is that blkdev_get when called on a partition needs to > lock (bd_mutex) the partition and the whole device. lockdep would > normally see this as a possible deadlock and needs to be told that > this particular nesting is known to be safe. > > The code to do this is in -linus is rather messy, largely because the > locking itself is messy. The bd_mutex for the whole is taken several > times while bd_mutex for the partition is held, and it is taken at > both levels of the recursion (blkdev_get calls blkdev_get - only to > one level). > > As key observation to simplifying the locking is to observer that a > lot of the locking is there to protect the updating of bd_part_count. > If those updates are moved, the locking can become simpler. > > The first patch removes the current approach in -mm to handling this > nesting and explains why it is not ideal. > This reverts new-bd_mutex-lockdep-annotation.patch > > The second simplifies the locking as explained above. > > The third adds the mutex_lock_nested annotations, which are now trivial. > > The last fixes a tangentially related lockdep problem in md - there is > a false relationship between bd_mutex and md->reconfig_mutex which > needs to be clarified. > > [PATCH 000 of 4] Introduction > [PATCH 001 of 4] Remove lock_key approach to managing nested bd_mutex locks. > [PATCH 002 of 4] Simplify some aspects of bd_mutex nesting. > [PATCH 003 of 4] Use mutex_lock_nested for bd_mutex to avoid lockdep warning. > [PATCH 004 of 4] Avoid lockdep warning in md.
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
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