From f6d8fea9e3953151a4adb4f603503dc3dc9c69da Mon Sep 17 00:00:00 2001 From: Matthew Maurer Date: Fri, 3 Apr 2026 18:18:58 +0000 Subject: [PATCH] rust_binder: Avoid holding lock when dropping delivered_death In 6c37bebd8c926, we switched to looping over the list and dropping each individual node, ostensibly without the lock held in the loop body. If the kernel were using Rust Edition 2024, the comment would be accurate, and the lock would not be held across the drop. However, the kernel is currently using 2021, so tail expression lifetime extension results in the lock being held across the drop. Explicitly binding the expression result to a variable makes the lockguard no longer part of a tail expression, causing the lock to be dropped before entering the loop body. This was detected via `CONFIG_PROVE_LOCKING` identifying an invalid wait context at the drop site. Reported-by: David Stevens Signed-off-by: Matthew Maurer Cc: stable Fixes: 6c37bebd8c92 ("rust_binder: avoid mem::take on delivered_deaths") Reviewed-by: Alice Ryhl Acked-by: Carlos Llamas Link: https://patch.msgid.link/20260403-lockhold-v1-1-c332b56cd8ae@google.com Signed-off-by: Greg Kroah-Hartman --- drivers/android/binder/process.rs | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/drivers/android/binder/process.rs b/drivers/android/binder/process.rs index 820cbd541435..96b8440ceac6 100644 --- a/drivers/android/binder/process.rs +++ b/drivers/android/binder/process.rs @@ -1402,7 +1402,12 @@ impl Process { // Clear delivered_deaths list. // // Scope ensures that MutexGuard is dropped while executing the body. - while let Some(delivered_death) = { self.inner.lock().delivered_deaths.pop_front() } { + while let Some(delivered_death) = { + // Explicitly bind to avoid tail expression lifetime extension of the lockguard + // Can be removed when the kernel moves to edition 2024 + let maybe_death = self.inner.lock().delivered_deaths.pop_front(); + maybe_death + } { drop(delivered_death); } -- 2.47.3