From 2f42f1eb9093834b635991c70d0273fbe249eabf Mon Sep 17 00:00:00 2001 From: Al Viro Date: Mon, 30 Oct 2023 01:09:50 -0400 Subject: Call retain_dentry() with refcount 0 Instead of bumping it from 0 to 1, calling retain_dentry(), then decrementing it back to 0 (with ->d_lock held all the way through), just leave refcount at 0 through all of that. It will have a visible effect for ->d_delete() - now it can be called with refcount 0 instead of 1 and it can no longer play silly buggers with dropping/regaining ->d_lock. Not that any in-tree instances tried to (it's pretty hard to get right). Any out-of-tree ones will have to adjust (assuming they need any changes). Note that we do not need to extend rcu-critical area here - we have verified that refcount is non-negative after having grabbed ->d_lock, so nobody will be able to free dentry until they get into __dentry_kill(), which won't happen until they manage to grab ->d_lock. Reviewed-by: Christian Brauner Signed-off-by: Al Viro --- Documentation/filesystems/porting.rst | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'Documentation/filesystems/porting.rst') diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst index 331405f4b29f..da8073b592ff 100644 --- a/Documentation/filesystems/porting.rst +++ b/Documentation/filesystems/porting.rst @@ -1070,3 +1070,11 @@ The list of children anchored in parent dentry got turned into hlist now. Field names got changed (->d_children/->d_sib instead of ->d_subdirs/->d_child for anchor/entries resp.), so any affected places will be immediately caught by compiler. + +--- + +**mandatory** + +->d_delete() instances are now called for dentries with ->d_lock held +and refcount equal to 0. They are not permitted to drop/regain ->d_lock. +None of in-tree instances did anything of that sort. Make sure yours do not... -- cgit v1.2.3