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-rw-r--r--kernel/bpf/mmap_unlock_work.h65
1 files changed, 65 insertions, 0 deletions
diff --git a/kernel/bpf/mmap_unlock_work.h b/kernel/bpf/mmap_unlock_work.h
new file mode 100644
index 000000000..5d18d7d85
--- /dev/null
+++ b/kernel/bpf/mmap_unlock_work.h
@@ -0,0 +1,65 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/* Copyright (c) 2021 Facebook
+ */
+
+#ifndef __MMAP_UNLOCK_WORK_H__
+#define __MMAP_UNLOCK_WORK_H__
+#include <linux/irq_work.h>
+
+/* irq_work to run mmap_read_unlock() in irq_work */
+struct mmap_unlock_irq_work {
+ struct irq_work irq_work;
+ struct mm_struct *mm;
+};
+
+DECLARE_PER_CPU(struct mmap_unlock_irq_work, mmap_unlock_work);
+
+/*
+ * We cannot do mmap_read_unlock() when the irq is disabled, because of
+ * risk to deadlock with rq_lock. To look up vma when the irqs are
+ * disabled, we need to run mmap_read_unlock() in irq_work. We use a
+ * percpu variable to do the irq_work. If the irq_work is already used
+ * by another lookup, we fall over.
+ */
+static inline bool bpf_mmap_unlock_get_irq_work(struct mmap_unlock_irq_work **work_ptr)
+{
+ struct mmap_unlock_irq_work *work = NULL;
+ bool irq_work_busy = false;
+
+ if (irqs_disabled()) {
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
+ work = this_cpu_ptr(&mmap_unlock_work);
+ if (irq_work_is_busy(&work->irq_work)) {
+ /* cannot queue more up_read, fallback */
+ irq_work_busy = true;
+ }
+ } else {
+ /*
+ * PREEMPT_RT does not allow to trylock mmap sem in
+ * interrupt disabled context. Force the fallback code.
+ */
+ irq_work_busy = true;
+ }
+ }
+
+ *work_ptr = work;
+ return irq_work_busy;
+}
+
+static inline void bpf_mmap_unlock_mm(struct mmap_unlock_irq_work *work, struct mm_struct *mm)
+{
+ if (!work) {
+ mmap_read_unlock(mm);
+ } else {
+ work->mm = mm;
+
+ /* The lock will be released once we're out of interrupt
+ * context. Tell lockdep that we've released it now so
+ * it doesn't complain that we forgot to release it.
+ */
+ rwsem_release(&mm->mmap_lock.dep_map, _RET_IP_);
+ irq_work_queue(&work->irq_work);
+ }
+}
+
+#endif /* __MMAP_UNLOCK_WORK_H__ */