[PATCH 5.10 066/406] eventfd: Export eventfd_ctx_do_read()

Greg Kroah-Hartman
2023-09-17T19:22:02Z

From: David Woodhouse <dwmw@amazon.co.uk>

[ Upstream commit 28f1326710555bbe666f64452d08f2d7dd657cae ]

Where events are consumed in the kernel, for example by KVM's
irqfd_wakeup() and VFIO's virqfd_wakeup(), they currently lack a
mechanism to drain the eventfd's counter.

Since the wait queue is already locked while the wakeup functions are
invoked, all they really need to do is call eventfd_ctx_do_read().

Add a check for the lock, and export it for them.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20201027135523.646811-2-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Stable-dep-of: 758b49204781 ("eventfd: prevent underflow for eventfd semaphores")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/eventfd.c | 5 ++++-
include/linux/eventfd.h | 6 ++++++
2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/eventfd.c b/fs/eventfd.c
index 4a14295cffe0d..b8d38b970ce7f 100644
--- a/fs/eventfd.c
+++ b/fs/eventfd.c
@@ -187,11 +187,14 @@ static __poll_t eventfd_poll(struct file *file, poll_table *wait)
return events;
}

-static void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt)
+void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt)
{
+ lockdep_assert_held(&ctx->wqh.lock);
+
*cnt = (ctx->flags & EFD_SEMAPHORE) ? 1 : ctx->count;
ctx->count -= *cnt;
}
+EXPORT_SYMBOL_GPL(eventfd_ctx_do_read);

/**
* eventfd_ctx_remove_wait_queue - Read the current counter and removes wait queue.
diff --git a/include/linux/eventfd.h b/include/linux/eventfd.h
index 6cd2a92daf205..c1bd4883e2faf 100644
--- a/include/linux/eventfd.h
+++ b/include/linux/eventfd.h
@@ -42,6 +42,7 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n);
__u64 eventfd_signal_mask(struct eventfd_ctx *ctx, __u64 n, unsigned mask);
int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_entry_t *wait,
__u64 *cnt);
+void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt);

DECLARE_PER_CPU(int, eventfd_wake_count);

@@ -89,6 +90,11 @@ static inline bool eventfd_signal_count(void)
return false;
}

+static inline void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt)
+{
+
+}
+
#endif

#endif /* _LINUX_EVENTFD_H */
--
2.40.1