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 --- 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;