On Mon, Sep 17, 2012 at 10:23:30PM +0200, Miklos Szeredi wrote: > From: Miklos Szeredi <mszeredi@xxxxxxx> > > IBM reported a deadlock in select_parent(). This was found to be caused by > taking rename_lock when already locked when restarting the tree traversal. > > There are two cases when the traversal needs to be restarted: > > 1) concurrent d_move(); this can only happen when not already locked, > since taking rename_lock protects against concurrent d_move(). > > 2) racing with final d_put() on child just at the moment of ascending > to parent; rename_lock doesn't protect against this rare race, so it > can happen when already locked. > > Because of case 2. we need to be able to handle restarting the traversal > when rename_lock is already held. This patch fixes all three callers of > try_to_ascend(). > > IBM reported that the deadlock is gone with this patch. However, there's still > a soft lockup which is addressed by the next patch. Egads... The problem is real and analysis, AFAICS, is correct, but result is extremely ugly ;-/ Let me try to come up with something saner; I'll push that one to Linus if nothing better comes to mind, but I'd really prefer to avoid adding to ugliness in fs/dcache.c - we already have too much of that... -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
