#include <linux/seq_file.h>
#include <linux/idr.h>
+DEFINE_PER_CPU(int, eventfd_wake_count);
+
static DEFINE_IDA(eventfd_ida);
struct eventfd_ctx {
{
unsigned long flags;
+ /*
+ * Deadlock or stack overflow issues can happen if we recurse here
+ * through waitqueue wakeup handlers. If the caller users potentially
+ * nested waitqueues with custom wakeup handlers, then it should
+ * check eventfd_signal_count() before calling this function. If
+ * it returns true, the eventfd_signal() call should be deferred to a
+ * safe context.
+ */
+ if (WARN_ON_ONCE(this_cpu_read(eventfd_wake_count)))
+ return 0;
+
spin_lock_irqsave(&ctx->wqh.lock, flags);
+ this_cpu_inc(eventfd_wake_count);
if (ULLONG_MAX - ctx->count < n)
n = ULLONG_MAX - ctx->count;
ctx->count += n;
if (waitqueue_active(&ctx->wqh))
wake_up_locked_poll(&ctx->wqh, EPOLLIN);
+ this_cpu_dec(eventfd_wake_count);
spin_unlock_irqrestore(&ctx->wqh.lock, flags);
return n;