From b5e683d5cab8cd433b06ae178621f083cabd4f63 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Sun, 2 Feb 2020 08:23:03 -0700 Subject: eventfd: track eventfd_signal() recursion depth eventfd use cases from aio and io_uring can deadlock due to circular or resursive calling, when eventfd_signal() tries to grab the waitqueue lock. On top of that, it's also possible to construct notification chains that are deep enough that we could blow the stack. Add a percpu counter that tracks the percpu recursion depth, warn if we exceed it. The counter is also exposed so that users of eventfd_signal() can do the right thing if it's non-zero in the context where it is called. Cc: stable@vger.kernel.org # 4.19+ Signed-off-by: Jens Axboe --- include/linux/eventfd.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'include/linux') diff --git a/include/linux/eventfd.h b/include/linux/eventfd.h index ffcc7724ca21..dc4fd8a6644d 100644 --- a/include/linux/eventfd.h +++ b/include/linux/eventfd.h @@ -12,6 +12,8 @@ #include #include #include +#include +#include /* * CAREFUL: Check include/uapi/asm-generic/fcntl.h when defining @@ -40,6 +42,13 @@ __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); +DECLARE_PER_CPU(int, eventfd_wake_count); + +static inline bool eventfd_signal_count(void) +{ + return this_cpu_read(eventfd_wake_count); +} + #else /* CONFIG_EVENTFD */ /* @@ -68,6 +77,11 @@ static inline int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, return -ENOSYS; } +static inline bool eventfd_signal_count(void) +{ + return false; +} + #endif #endif /* _LINUX_EVENTFD_H */ -- cgit v1.2.3-59-g8ed1b