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eventfd: Export eventfd_ctx_do_read() 

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>
This commit is contained in:
David Woodhouse 2020-10-27 13:55:21 +00:00 committed by Paolo Bonzini
parent e8dbf19508
commit 28f1326710
2 changed files with 10 additions and 1 deletions
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5
fs/eventfd.c
View File

@ -182,11 +182,14 @@ 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.

6
include/linux/eventfd.h
View File

@ -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 */