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 <axboe@kernel.dk>
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2 changed files with 29 additions and 0 deletions
15
fs/eventfd.c
15
fs/eventfd.c
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@ -24,6 +24,8 @@
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#include <linux/seq_file.h>
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#include <linux/seq_file.h>
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#include <linux/idr.h>
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#include <linux/idr.h>
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DEFINE_PER_CPU(int, eventfd_wake_count);
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static DEFINE_IDA(eventfd_ida);
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static DEFINE_IDA(eventfd_ida);
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struct eventfd_ctx {
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struct eventfd_ctx {
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@ -60,12 +62,25 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n)
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{
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{
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unsigned long flags;
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unsigned long flags;
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/*
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* Deadlock or stack overflow issues can happen if we recurse here
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* through waitqueue wakeup handlers. If the caller users potentially
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* nested waitqueues with custom wakeup handlers, then it should
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* check eventfd_signal_count() before calling this function. If
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* it returns true, the eventfd_signal() call should be deferred to a
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* safe context.
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*/
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if (WARN_ON_ONCE(this_cpu_read(eventfd_wake_count)))
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return 0;
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spin_lock_irqsave(&ctx->wqh.lock, flags);
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spin_lock_irqsave(&ctx->wqh.lock, flags);
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this_cpu_inc(eventfd_wake_count);
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if (ULLONG_MAX - ctx->count < n)
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if (ULLONG_MAX - ctx->count < n)
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n = ULLONG_MAX - ctx->count;
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n = ULLONG_MAX - ctx->count;
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ctx->count += n;
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ctx->count += n;
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if (waitqueue_active(&ctx->wqh))
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if (waitqueue_active(&ctx->wqh))
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wake_up_locked_poll(&ctx->wqh, EPOLLIN);
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wake_up_locked_poll(&ctx->wqh, EPOLLIN);
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this_cpu_dec(eventfd_wake_count);
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spin_unlock_irqrestore(&ctx->wqh.lock, flags);
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spin_unlock_irqrestore(&ctx->wqh.lock, flags);
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return n;
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return n;
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@ -12,6 +12,8 @@
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#include <linux/fcntl.h>
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#include <linux/fcntl.h>
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#include <linux/wait.h>
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#include <linux/wait.h>
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#include <linux/err.h>
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#include <linux/err.h>
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#include <linux/percpu-defs.h>
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#include <linux/percpu.h>
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/*
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/*
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* CAREFUL: Check include/uapi/asm-generic/fcntl.h when defining
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* CAREFUL: Check include/uapi/asm-generic/fcntl.h when defining
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@ -40,6 +42,13 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n);
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int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_entry_t *wait,
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int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_entry_t *wait,
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__u64 *cnt);
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__u64 *cnt);
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DECLARE_PER_CPU(int, eventfd_wake_count);
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static inline bool eventfd_signal_count(void)
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{
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return this_cpu_read(eventfd_wake_count);
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}
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#else /* CONFIG_EVENTFD */
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#else /* CONFIG_EVENTFD */
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/*
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/*
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@ -68,6 +77,11 @@ static inline int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx,
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return -ENOSYS;
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return -ENOSYS;
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}
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}
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static inline bool eventfd_signal_count(void)
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{
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return false;
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}
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#endif
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#endif
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#endif /* _LINUX_EVENTFD_H */
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#endif /* _LINUX_EVENTFD_H */
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