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Subject[PATCH 6/8] mmap locking API: add mmap_read_release() and mmap_read_unlock_non_owner()
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Add a couple APIs to allow splitting mmap_read_unlock() into two calls:
- mmap_read_release(), called by the task that had taken the mmap lock;
- mmap_read_unlock_non_owner(), called from a work queue.

These apis are used by kernel/bpf/stackmap.c only.

Signed-off-by: Michel Lespinasse <walken@google.com>
---
include/linux/mmap_lock.h | 10 ++++++++++
kernel/bpf/stackmap.c | 9 ++++-----
2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
index 40a972a26857..00d6cc02581d 100644
--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h
@@ -62,6 +62,16 @@ static inline void mmap_read_unlock(struct mm_struct *mm)
up_read(&mm->mmap_sem);
}

+static inline void mmap_read_release(struct mm_struct *mm, unsigned long ip)
+{
+ rwsem_release(&mm->mmap_sem.dep_map, ip);
+}
+
+static inline void mmap_read_unlock_non_owner(struct mm_struct *mm)
+{
+ up_read_non_owner(&mm->mmap_sem);
+}
+
static inline bool mmap_is_locked(struct mm_struct *mm)
{
return rwsem_is_locked(&mm->mmap_sem) != 0;
diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index f2115f691577..413b512a99eb 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -33,7 +33,7 @@ struct bpf_stack_map {
/* irq_work to run up_read() for build_id lookup in nmi context */
struct stack_map_irq_work {
struct irq_work irq_work;
- struct rw_semaphore *sem;
+ struct mm_struct *mm;
};

static void do_up_read(struct irq_work *entry)
@@ -41,8 +41,7 @@ static void do_up_read(struct irq_work *entry)
struct stack_map_irq_work *work;

work = container_of(entry, struct stack_map_irq_work, irq_work);
- up_read_non_owner(work->sem);
- work->sem = NULL;
+ mmap_read_unlock_non_owner(work->mm);
}

static DEFINE_PER_CPU(struct stack_map_irq_work, up_read_work);
@@ -332,14 +331,14 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
if (!work) {
mmap_read_unlock(current->mm);
} else {
- work->sem = &current->mm->mmap_sem;
+ work->mm = current->mm;
irq_work_queue(&work->irq_work);
/*
* The irq_work will release the mmap_sem with
* up_read_non_owner(). The rwsem_release() is called
* here to release the lock from lockdep's perspective.
*/
- rwsem_release(&current->mm->mmap_sem.dep_map, _RET_IP_);
+ mmap_read_release(current->mm, _RET_IP_);
}
}

--
2.25.1.696.g5e7596f4ac-goog
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