Re: [PATCH v8 03/10] eventfd: Increase the recursion depth of eventfd_signal()
From: He Zhe <hidden>
Date: 2021-06-17 08:35:02
Also in:
kvm, linux-fsdevel, linux-iommu, lkml, virtualization
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 <redacted>
Acked-by: Jason Wang <redacted>The fix had been posted one year ago. https://lore.kernel.org/lkml/20200410114720.24838-1-zhe.he@windriver.com/ (local)
quoted hunk ↗ jump to hunk
--- 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 */