From a10639966fd72fff8f7fbf3c8e733307daabd38f Mon Sep 17 00:00:00 2001 From: Danilo Krummrich Date: Sun, 28 Jun 2026 22:02:53 +0200 Subject: [PATCH] rust: devres: ensure revocation is complete before device finishes unbinding Now that the revocation Completion is in place, also address the symmetric case. When Devres::drop() wins the is_available swap and the devres callback loses, the callback returns to devres_release_all() without waiting. This means device unbinding can complete while Devres::drop() is still executing drop_in_place() on another CPU, which is a problem if T's destructor accesses device state. Make the synchronization bidirectional. Whichever side performs drop_in_place() signals the Completion, and the other side waits. This does not reintroduce the nested Devres deadlock fixed by commit ba268514ea14 ("rust: devres: fix race condition due to nesting"), because that deadlock was caused by drop waiting for the release callback to return (the old 'devm' Completion). Here, both sides only wait for drop_in_place() to finish, which completes within the current call chain. The Arc> keeps the Inner allocation alive independently. Cc: stable@vger.kernel.org Fixes: ba268514ea14 ("rust: devres: fix race condition due to nesting") Reviewed-by: Gary Guo Reviewed-by: Alice Ryhl Link: https://patch.msgid.link/20260628200304.2365598-1-dakr@kernel.org Signed-off-by: Danilo Krummrich --- rust/kernel/devres.rs | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/rust/kernel/devres.rs b/rust/kernel/devres.rs index 4a1e5eec78ab..ebb5c19e851e 100644 --- a/rust/kernel/devres.rs +++ b/rust/kernel/devres.rs @@ -269,6 +269,11 @@ impl Devres { if inner.data.revoke() { inner.revocation.complete_all(); + } else { + // Devres::drop() is concurrently revoking; wait for it to finish `drop_in_place()` + // before returning to `devres_release_all()`, ensuring `T` is fully torn down before + // the device finishes unbinding. + inner.revocation.wait_for_completion(); } } @@ -366,6 +371,8 @@ impl Drop for Devres { // SAFETY: When `drop` runs, it is guaranteed that nobody is accessing the revocable data // anymore, hence it is safe not to wait for the grace period to finish. if unsafe { self.data().revoke_nosync() } { + self.inner.revocation.complete_all(); + // We revoked `self.data` before devres did, hence try to remove it. if self.remove_node() { // SAFETY: In `Self::new` we have taken an additional reference count of `self.data`