[PATCH v6 02/10] eventfd: Increase the recursion depth of eventfd_signal()
From: Xie Yongji <hidden>
Date: 2021-03-31 08:07:23
Also in:
kvm, linux-fsdevel
Subsystem:
filesystems (vfs and infrastructure), the rest · Maintainers:
Alexander Viro, Christian Brauner, Linus Torvalds
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 <jasowang@redhat.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; } #else /* CONFIG_EVENTFD */
--
2.11.0