This is identical to eventfd_signal(), but it allows the caller to pass in a mask to be used for the poll wakeup key. The use case is avoiding repeated multishot triggers if we have a dependency between eventfd and io_uring.
If we setup an eventfd context and register that as the io_uring eventfd, and at the same time queue a multishot poll request for the eventfd context, then any CQE posted will repeatedly trigger the multishot request until it terminates when the CQ ring overflows.
In preparation for io_uring detecting this circular dependency, add the mentioned helper so that io_uring can pass in EPOLL_URING as part of the poll wakeup key.
Cc: stable@vger.kernel.org # 6.0 Signed-off-by: Jens Axboe axboe@kernel.dk --- fs/eventfd.c | 37 +++++++++++++++++++++---------------- include/linux/eventfd.h | 1 + 2 files changed, 22 insertions(+), 16 deletions(-)
diff --git a/fs/eventfd.c b/fs/eventfd.c index c0ffee99ad23..249ca6c0b784 100644 --- a/fs/eventfd.c +++ b/fs/eventfd.c @@ -43,21 +43,7 @@ struct eventfd_ctx { int id; };
-/** - * eventfd_signal - Adds @n to the eventfd counter. - * @ctx: [in] Pointer to the eventfd context. - * @n: [in] Value of the counter to be added to the eventfd internal counter. - * The value cannot be negative. - * - * This function is supposed to be called by the kernel in paths that do not - * allow sleeping. In this function we allow the counter to reach the ULLONG_MAX - * value, and we signal this as overflow condition by returning a EPOLLERR - * to poll(2). - * - * Returns the amount by which the counter was incremented. This will be less - * than @n if the counter has overflowed. - */ -__u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n) +__u64 eventfd_signal_mask(struct eventfd_ctx *ctx, __u64 n, unsigned mask) { unsigned long flags;
@@ -78,12 +64,31 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n) n = ULLONG_MAX - ctx->count; ctx->count += n; if (waitqueue_active(&ctx->wqh)) - wake_up_locked_poll(&ctx->wqh, EPOLLIN); + wake_up_locked_poll(&ctx->wqh, EPOLLIN | mask); current->in_eventfd = 0; spin_unlock_irqrestore(&ctx->wqh.lock, flags);
return n; } + +/** + * eventfd_signal - Adds @n to the eventfd counter. + * @ctx: [in] Pointer to the eventfd context. + * @n: [in] Value of the counter to be added to the eventfd internal counter. + * The value cannot be negative. + * + * This function is supposed to be called by the kernel in paths that do not + * allow sleeping. In this function we allow the counter to reach the ULLONG_MAX + * value, and we signal this as overflow condition by returning a EPOLLERR + * to poll(2). + * + * Returns the amount by which the counter was incremented. This will be less + * than @n if the counter has overflowed. + */ +__u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n) +{ + return eventfd_signal_mask(ctx, n, 0); +} EXPORT_SYMBOL_GPL(eventfd_signal);
static void eventfd_free_ctx(struct eventfd_ctx *ctx) diff --git a/include/linux/eventfd.h b/include/linux/eventfd.h index 30eb30d6909b..e849329ce1a8 100644 --- a/include/linux/eventfd.h +++ b/include/linux/eventfd.h @@ -40,6 +40,7 @@ struct file *eventfd_fget(int fd); struct eventfd_ctx *eventfd_ctx_fdget(int fd); struct eventfd_ctx *eventfd_ctx_fileget(struct file *file); __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);