On Tue, Jul 5, 2022 at 9:30 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > On Tue, Jul 05, 2022 at 09:26:47PM +0100, Filipe Manana wrote: > > In this case we can actually call xa_insert() without holding that > > spinlock, it's safe against other concurrent calls to > > btrfs_get_or_create_delayed_node(), btrfs_get_delayed_node(), > > btrfs_kill_delayed_inode_items(), etc. > > > > However, looking at xa_insert() we have: > > > > xa_lock(xa); > > err = __xa_insert(xa, index, entry, gfp); > > xa_unlock(xa); > > > > And xa_lock() is defined as: > > > > #define xa_lock(xa) spin_lock(&(xa)->xa_lock) > > > > So we'll always be under a spinlock even if we change btrfs to not > > take the root->inode_lock spinlock. > > > > This seems more like a general problem outside btrfs' control. > > So CC'ing Willy to double check. > > No, the XArray knows about its own spinlock. It'll drop it if it needs > to allocate memory and the GFP flags indicate that the caller can sleep. > It doesn't know about your spinlock, so it can't do the same thing for > you ;-) Ah, that's good to know. Thanks Willy.
