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FROMGIT: kfence: avoid stalling work queue task without allocations

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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 <elver@google.com>
Reported-by: Anders Roxell <anders.roxell@linaro.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: SeongJae Park <sjpark@amazon.de>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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 <glider@google.com>
Change-Id: I2332ff8144b8bce5c4574b01ea2863e0e71e6124
This commit is contained in:
Marco Elver 2021-01-22 09:18:32 +00:00 • committed by Michael Bestas
commit c28a209911
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1 changed files with 5 additions and 1 deletions
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6
mm/kfence/core.c
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@ -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);