On Wed, Apr 15, 2015 at 01:36:33PM +0100, Al Viro wrote: > al@duke:~/linux/trees/vfs$ git grep -n -w kdbus_node_idr_lock > ipc/kdbus/node.c:237:static DECLARE_RWSEM(kdbus_node_idr_lock); > ipc/kdbus/node.c:340: down_write(&kdbus_node_idr_lock); > ipc/kdbus/node.c:344: up_write(&kdbus_node_idr_lock); > ipc/kdbus/node.c:444: down_write(&kdbus_node_idr_lock); > ipc/kdbus/node.c:452: up_write(&kdbus_node_idr_lock);
Heh, that's a leftover from an older version, I'll go fix that up to be a simple mutex, which is all that this is doing here anyway. > Do you see anything wrong with that? Or with things like that: > mutex_lock(&pos->lock); > v_pre = atomic_read(&pos->active); > if (v_pre >= 0) > atomic_add_return(KDBUS_NODE_BIAS, &pos->active); > else if (v_pre == KDBUS_NODE_NEW) > atomic_set(&pos->active, KDBUS_NODE_RELEASE_DIRECT); > mutex_unlock(&pos->lock); > What are the locking rules for ->active/->waitq/->lock? Are those the > outermost thing in the hierarchy? Or is that dependent on the node location? > It sure as hell is outside of (at least) ->mmap_sem (by way of > kdbus_conn_connect() establishing that ->active/->waitq is outside of > ->conn_rwlock, which due to kdbus_bus_broadcast() nests outside of anything > taken by kdbus_meta_proc_collect(), which includes ->mmap_sem) and that alone > brings in a lot... > > Document your goddamn locking, would you? It *IS* new code, and you, as you > say, had very few people working on it, so you don't have the excuses for > the mess existing in older parts of the tree. Fair enough, documenting the locking is a good thing, that will make reviewing this easier, I'll go work on that. > Locking complexity in there is easily as bad as that of VFS sans the RCU fun; > sure, I can spend a week and (hopefully) document it for you, but I would > really prefer if you guys had done that. And I *do* appreciate the comments > in node.c, but they are nowhere near enough. Thanks, it's hard to balance the comment/code level at times. And yes, it is complex and should be explained better, will work on that. greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
