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SubjectRe: [PATCH v8 03/10] eventfd: Increase the recursion depth of eventfd_signal()
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On 6/15/21 10:13 PM, Xie Yongji wrote:
> Increase the recursion depth of eventfd_signal() to 1. This
> is the maximum recursion depth we have found so far, which
> can be triggered with the following call chain:
>
> kvm_io_bus_write [kvm]
> --> ioeventfd_write [kvm]
> --> eventfd_signal [eventfd]
> --> vhost_poll_wakeup [vhost]
> --> vduse_vdpa_kick_vq [vduse]
> --> eventfd_signal [eventfd]
>
> Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
> Acked-by: Jason Wang <jasowang@redhat.com>

The fix had been posted one year ago.

https://lore.kernel.org/lkml/20200410114720.24838-1-zhe.he@windriver.com/


> ---
> fs/eventfd.c | 2 +-
> include/linux/eventfd.h | 5 ++++-
> 2 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/fs/eventfd.c b/fs/eventfd.c
> index e265b6dd4f34..cc7cd1dbedd3 100644
> --- a/fs/eventfd.c
> +++ b/fs/eventfd.c
> @@ -71,7 +71,7 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n)
> * it returns true, the eventfd_signal() call should be deferred to a
> * safe context.
> */
> - if (WARN_ON_ONCE(this_cpu_read(eventfd_wake_count)))
> + if (WARN_ON_ONCE(this_cpu_read(eventfd_wake_count) > EFD_WAKE_DEPTH))
> return 0;
>
> spin_lock_irqsave(&ctx->wqh.lock, flags);
> diff --git a/include/linux/eventfd.h b/include/linux/eventfd.h
> index fa0a524baed0..886d99cd38ef 100644
> --- a/include/linux/eventfd.h
> +++ b/include/linux/eventfd.h
> @@ -29,6 +29,9 @@
> #define EFD_SHARED_FCNTL_FLAGS (O_CLOEXEC | O_NONBLOCK)
> #define EFD_FLAGS_SET (EFD_SHARED_FCNTL_FLAGS | EFD_SEMAPHORE)
>
> +/* Maximum recursion depth */
> +#define EFD_WAKE_DEPTH 1
> +
> struct eventfd_ctx;
> struct file;
>
> @@ -47,7 +50,7 @@ DECLARE_PER_CPU(int, eventfd_wake_count);
>
> static inline bool eventfd_signal_count(void)
> {
> - return this_cpu_read(eventfd_wake_count);
> + return this_cpu_read(eventfd_wake_count) > EFD_WAKE_DEPTH;

count is just count. How deep is acceptable should be put
where eventfd_signal_count is called.


Zhe

> }
>
> #else /* CONFIG_EVENTFD */

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