From c28a20991103490ca4f6e2192c0274e591aa803a Mon Sep 17 00:00:00 2001 From: Marco Elver Date: Fri, 22 Jan 2021 09:18:32 +0000 Subject: [PATCH] FROMGIT: 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 Bug: 177201466 (cherry picked from commit 80d4693491f6f20de01437319b081fdda2079e67 https://github.com/hnaz/linux-mm v5.11-rc4-mmots-2021-01-21-20-10) Test: CONFIG_KFENCE_KUNIT_TEST=y passes on Cuttlefish Signed-off-by: Alexander Potapenko Change-Id: I2332ff8144b8bce5c4574b01ea2863e0e71e6124 --- 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 4972cc6217dd..1624b7ee6868 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);