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 <[email protected]>
---
fs/eventfd.c | 10 +++++++---
include/linux/eventfd.h | 2 +-
include/linux/sched.h | 2 +-
3 files changed, 9 insertions(+), 5 deletions(-)
diff --git a/fs/eventfd.c b/fs/eventfd.c
index 3627dd7d25db..c0ffee99ad23 100644
--- a/fs/eventfd.c
+++ b/fs/eventfd.c
@@ -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);
diff --git a/include/linux/eventfd.h b/include/linux/eventfd.h
index 305d5f19093b..30eb30d6909b 100644
--- a/include/linux/eventfd.h
+++ b/include/linux/eventfd.h
@@ -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 */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index e7b2f8a5c711..8d82d6d32670 100644
--- 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;
--
2.30.2
On 8/16/22 07:59, Dylan Yudaken wrote:
> 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);
> }
Reviewed-by: Jens Axboe <[email protected]>
--
Jens Axboe
On Tue, 16 Aug 2022 06:59:59 -0700, Dylan Yudaken wrote:
> 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:
>
> [...]
Applied, thanks!
[1/1] eventfd: guard wake_up in eventfd fs calls as well
commit: 07106d2635a6d1eb55bb13e6c89c92ae5483b050
Best regards,
--
Jens Axboe