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Commit 3e9617d6 authored by David Woodhouse's avatar David Woodhouse Committed by Greg Kroah-Hartman
Browse files

eventfd: Export eventfd_ctx_do_read() 



[ 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: default avatarDavid Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20201027135523.646811-2-dwmw2@infradead.org>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Stable-dep-of: 758b49204781 ("eventfd: prevent underflow for eventfd semaphores")
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent f59ff666

fs/eventfd.c

+4 −1
Original line number Diff line number Diff line
@@ -181,11 +181,14 @@ 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.

include/linux/eventfd.h

+6 −0
Original line number Diff line number Diff line
@@ -41,6 +41,7 @@ struct eventfd_ctx *eventfd_ctx_fileget(struct file *file); 
__u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n);

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);
@@ -82,6 +83,11 @@ 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 */