From: Jens Axboe <ax...@kernel.dk>
[ Upstream commit fd7d6de2241453fc7d042336d366a939a25bc5a9 ]
If an application is doing reads on signalfd, and we arm the poll handler
because there's no data available, then the wakeup can recurse on the
tasks sighand->siglock as the signal delivery from task_work_add() will
use TWA_SIGNAL and that attempts to lock it again.
We can detect the signalfd case pretty easily by comparing the poll->head
wait_queue_head_t with the target task signalfd wait queue. Just use
normal task wakeup for this case.
Cc: sta...@vger.kernel.org # v5.7+
Signed-off-by: Jens Axboe <ax...@kernel.dk>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
fs/io_uring.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index b966e2b8a77da..c384caad64665 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4114,7 +4114,8 @@ struct io_poll_table {
int error;
};
-static int io_req_task_work_add(struct io_kiocb *req, struct callback_head *cb)
+static int io_req_task_work_add(struct io_kiocb *req, struct callback_head *cb,
+ bool twa_signal_ok)
{
struct task_struct *tsk = req->task;
struct io_ring_ctx *ctx = req->ctx;
@@ -4127,7 +4128,7 @@ static int io_req_task_work_add(struct io_kiocb *req,
struct callback_head *cb)
* will do the job.
*/
notify = 0;
- if (!(ctx->flags & IORING_SETUP_SQPOLL))
+ if (!(ctx->flags & IORING_SETUP_SQPOLL) && twa_signal_ok)
notify = TWA_SIGNAL;
ret = task_work_add(tsk, cb, notify);
@@ -4141,6 +4142,7 @@ static int __io_async_wake(struct io_kiocb *req, struct
io_poll_iocb *poll,
__poll_t mask, task_work_func_t func)
{
struct task_struct *tsk;
+ bool twa_signal_ok;
int ret;
/* for instances that support it check for an event match first: */
@@ -4156,13 +4158,21 @@ static int __io_async_wake(struct io_kiocb *req, struct
io_poll_iocb *poll,
init_task_work(&req->task_work, func);
percpu_ref_get(&req->ctx->refs);
+ /*
+ * If we using the signalfd wait_queue_head for this wakeup, then
+ * it's not safe to use TWA_SIGNAL as we could be recursing on the
+ * tsk->sighand->siglock on doing the wakeup. Should not be needed
+ * either, as the normal wakeup will suffice.
+ */
+ twa_signal_ok = (poll->head != &req->task->sighand->signalfd_wqh);
+
/*
* If this fails, then the task is exiting. When a task exits, the
* work gets canceled, so just cancel this request as well instead
* of executing it. We can't safely execute it anyway, as we may not
* have the needed state needed for it anyway.
*/
- ret = io_req_task_work_add(req, &req->task_work);
+ ret = io_req_task_work_add(req, &req->task_work, twa_signal_ok);
if (unlikely(ret)) {
WRITE_ONCE(poll->canceled, true);
tsk = io_wq_get_task(req->ctx->io_wq);
--
2.25.1
