5.4-stable review patch. If anyone has any objections, please let me know.
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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 78e41c7c3d05b..26b3d821e9168 100644 --- a/fs/eventfd.c +++ b/fs/eventfd.c @@ -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. diff --git a/include/linux/eventfd.h b/include/linux/eventfd.h index 3482f9365a4db..de0ad39d4281f 100644 --- a/include/linux/eventfd.h +++ b/include/linux/eventfd.h @@ -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 */