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eventfd: guard wake_up in eventfd fs calls as well

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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>
This commit is contained in:
Dylan Yudaken 2022-08-16 06:59:59 -07:00 committed by Jens Axboe
parent 521a547ced
commit 9f0deaa12d
3 changed files with 9 additions and 5 deletions
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10
fs/eventfd.c
View file

@ -69,17 +69,17 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n)
* 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 *iocb, struct iov_iter *to)
__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 *file, const char __user *buf, size_t c
}
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);

2
include/linux/eventfd.h
View file

@ -46,7 +46,7 @@ void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt);
static inline bool eventfd_signal_allowed(void)
{
return !current->in_eventfd_signal;
return !current->in_eventfd;
}
#else /* CONFIG_EVENTFD */

2
include/linux/sched.h
View file

@ -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;