5.4-stable review patch. If anyone has any objections, please let me know.
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From: Carlos Llamas cmllamas@google.com
commit 31643d84b8c3d9c846aa0e20bc033e46c68c7e7d upstream.
With the introduction of binder_available_for_proc_work_ilocked() in commit 1b77e9dcc3da ("ANDROID: binder: remove proc waitqueue") a binder thread can only "wait_for_proc_work" after its thread->looper has been marked as BINDER_LOOPER_STATE_{ENTERED|REGISTERED}.
This means an unregistered reader risks waiting indefinitely for work since it never gets added to the proc->waiting_threads. If there are no further references to its waitqueue either the task will hang. The same applies to readers using the (e)poll interface.
I couldn't find the rationale behind this restriction. So this patch restores the previous behavior of allowing unregistered threads to "wait_for_proc_work". Note that an error message for this scenario, which had previously become unreachable, is now re-enabled.
Fixes: 1b77e9dcc3da ("ANDROID: binder: remove proc waitqueue") Cc: stable@vger.kernel.org Cc: Martijn Coenen maco@google.com Cc: Arve Hjønnevåg arve@google.com Signed-off-by: Carlos Llamas cmllamas@google.com Link: https://lore.kernel.org/r/20240711201452.2017543-1-cmllamas@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/android/binder.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)
--- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -932,9 +932,7 @@ static bool binder_has_work(struct binde static bool binder_available_for_proc_work_ilocked(struct binder_thread *thread) { return !thread->transaction_stack && - binder_worklist_empty_ilocked(&thread->todo) && - (thread->looper & (BINDER_LOOPER_STATE_ENTERED | - BINDER_LOOPER_STATE_REGISTERED)); + binder_worklist_empty_ilocked(&thread->todo); }
static void binder_wakeup_poll_threads_ilocked(struct binder_proc *proc,