From b877f1c9d08a7e6831791832cc64c8cd97200fb6 Mon Sep 17 00:00:00 2001 From: Marco Elver Date: Thu, 31 Dec 2020 22:04:32 +0000 Subject: [PATCH] kfence: avoid stalling work queue task without allocations To toggle the allocation gates, we set up a delayed work that calls toggle_allocation_gate(). Here we use wait_event() to await an allocation and subsequently disable the static branch again. However, if the kernel has stopped doing allocations entirely, we'd wait indefinitely, and stall the worker task. This may also result in the appropriate warnings if CONFIG_DETECT_HUNG_TASK=y. Therefore, introduce a 1 second timeout and use wait_event_timeout(). If the timeout is reached, the static branch is disabled and a new delayed work is scheduled to try setting up an allocation at a later time. Note that, this scenario is very unlikely during normal workloads once the kernel has booted and user space tasks are running. It can, however, happen during early boot after KFENCE has been enabled, when e.g. running tests that do not result in any allocations. Link: https://lkml.kernel.org/r/CADYN=9J0DQhizAGB0-jz4HOBBh+05kMBXb4c0cXMS7Qi5NAJiw@mail.gmail.com Link: https://lkml.kernel.org/r/20201110135320.3309507-1-elver@google.com Signed-off-by: Marco Elver Reported-by: Anders Roxell Cc: Alexander Potapenko Cc: Dmitry Vyukov Cc: SeongJae Park Cc: Jann Horn Signed-off-by: Andrew Morton --- mm/kfence/core.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/mm/kfence/core.c b/mm/kfence/core.c index 64f33b93223b..735ff1ec3a63 100644 --- a/mm/kfence/core.c +++ b/mm/kfence/core.c @@ -588,7 +588,11 @@ static void toggle_allocation_gate(struct work_struct *work) /* Enable static key, and await allocation to happen. */ atomic_set(&allocation_gate, 0); static_branch_enable(&kfence_allocation_key); - wait_event(allocation_wait, atomic_read(&allocation_gate) != 0); + /* + * Await an allocation. Timeout after 1 second, in case the kernel stops + * doing allocations, to avoid stalling this worker task for too long. + */ + wait_event_timeout(allocation_wait, atomic_read(&allocation_gate) != 0, HZ); /* Disable static key and reset timer. */ static_branch_disable(&kfence_allocation_key); -- 2.50.1