diff mbox series

[6.0,545/862] eventfd: guard wake_up in eventfd fs calls as well

Message ID 20221019083314.035666345@linuxfoundation.org
State New
Headers
Series None |

Commit Message

Greg KH Oct. 19, 2022, 8:30 a.m. UTC 
  From: Dylan Yudaken <dylany@fb.com>

[ Upstream commit 9f0deaa12d832f488500a5afe9b912e9b3cfc432 ]

Guard wakeups that the user can trigger, and that may end up triggering a
call back into eventfd_signal. This is in addition to the current approach
that only guards in eventfd_signal.

Rename in_eventfd_signal -> in_eventfd at the same time to reflect this.

Without this there would be a deadlock in the following code using libaio:

int main()
{
	struct io_context *ctx = NULL;
	struct iocb iocb;
	struct iocb *iocbs[] = { &iocb };
	int evfd;
        uint64_t val = 1;

	evfd = eventfd(0, EFD_CLOEXEC);
	assert(!io_setup(2, &ctx));
	io_prep_poll(&iocb, evfd, POLLIN);
	io_set_eventfd(&iocb, evfd);
	assert(1 == io_submit(ctx, 1, iocbs));
        write(evfd, &val, 8);
}

Signed-off-by: Dylan Yudaken <dylany@fb.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/r/20220816135959.1490641-1-dylany@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/eventfd.c            |   10 +++++++---
 include/linux/eventfd.h |    2 +-
 include/linux/sched.h   |    2 +-
 3 files changed, 9 insertions(+), 5 deletions(-)
diff mbox series

Patch

--- a/fs/eventfd.c
+++ b/fs/eventfd.c
@@ -69,17 +69,17 @@  __u64 eventfd_signal(struct eventfd_ctx
 	 * it returns false, the eventfd_signal() call should be deferred to a
 	 * safe context.
 	 */
-	if (WARN_ON_ONCE(current->in_eventfd_signal))
+	if (WARN_ON_ONCE(current->in_eventfd))
 		return 0;
 
 	spin_lock_irqsave(&ctx->wqh.lock, flags);
-	current->in_eventfd_signal = 1;
+	current->in_eventfd = 1;
 	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);
-	current->in_eventfd_signal = 0;
+	current->in_eventfd = 0;
 	spin_unlock_irqrestore(&ctx->wqh.lock, flags);
 
 	return n;
@@ -253,8 +253,10 @@  static ssize_t eventfd_read(struct kiocb
 		__set_current_state(TASK_RUNNING);
 	}
 	eventfd_ctx_do_read(ctx, &ucnt);
+	current->in_eventfd = 1;
 	if (waitqueue_active(&ctx->wqh))
 		wake_up_locked_poll(&ctx->wqh, EPOLLOUT);
+	current->in_eventfd = 0;
 	spin_unlock_irq(&ctx->wqh.lock);
 	if (unlikely(copy_to_iter(&ucnt, sizeof(ucnt), to) != sizeof(ucnt)))
 		return -EFAULT;
@@ -301,8 +303,10 @@  static ssize_t eventfd_write(struct file
 	}
 	if (likely(res > 0)) {
 		ctx->count += ucnt;
+		current->in_eventfd = 1;
 		if (waitqueue_active(&ctx->wqh))
 			wake_up_locked_poll(&ctx->wqh, EPOLLIN);
+		current->in_eventfd = 0;
 	}
 	spin_unlock_irq(&ctx->wqh.lock);
 
--- a/include/linux/eventfd.h
+++ b/include/linux/eventfd.h
@@ -46,7 +46,7 @@  void eventfd_ctx_do_read(struct eventfd_
 
 static inline bool eventfd_signal_allowed(void)
 {
-	return !current->in_eventfd_signal;
+	return !current->in_eventfd;
 }
 
 #else /* CONFIG_EVENTFD */
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -936,7 +936,7 @@  struct task_struct {
 #endif
 #ifdef CONFIG_EVENTFD
 	/* Recursion prevention for eventfd_signal() */
-	unsigned			in_eventfd_signal:1;
+	unsigned			in_eventfd:1;
 #endif
 #ifdef CONFIG_IOMMU_SVA
 	unsigned			pasid_activated:1;