The sqd->thread access in io_uring_cancel_generic is just for debug check
so we can safely ignore the data race.
The sqd->thread access in io_uring_try_cancel_requests is to check if the
caller is the sq threadi with the check ctx->sq_data->thread == current. In
case this is called in a task other than the sq thread, we expect the
expression to be false. And in that case, the sq_data->thread read can race
with the NULL write in the sq thread termination. However, the race will
still make ctx->sq_data->thread == current be false, so we can safely
ignore the data race.
Reported-by: syzbot+3c750be01dab672c513d@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: Li Zetao <lizetao1@xxxxxxxxxx>
Signed-off-by: Bui Quang Minh <minhquangbui99@xxxxxxxxx>
---
io_uring/io_uring.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index ff691f37462c..b1a116620ae1 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -3094,9 +3094,18 @@ static __cold bool io_uring_try_cancel_requests(struct io_ring_ctx *ctx,
ret |= (cret != IO_WQ_CANCEL_NOTFOUND);
}
- /* SQPOLL thread does its own polling */
+ /*
+ * SQPOLL thread does its own polling
+ *
+ * We expect ctx->sq_data->thread == current to be false when
+ * this function is called on a task other than the sq thread.
+ * In that case, the sq_data->thread read can race with the
+ * NULL write in the sq thread termination. However, the race
+ * will still make ctx->sq_data->thread == current be false,
+ * so we can safely ignore the data race here.
+ */
if ((!(ctx->flags & IORING_SETUP_SQPOLL) && cancel_all) ||
- (ctx->sq_data && ctx->sq_data->thread == current)) {
+ (ctx->sq_data && data_race(ctx->sq_data->thread) == current)) {
while (!wq_list_empty(&ctx->iopoll_list)) {
io_iopoll_try_reap_events(ctx);
ret = true;
@@ -3142,7 +3151,7 @@ __cold void io_uring_cancel_generic(bool cancel_all, struct io_sq_data *sqd)
s64 inflight;
DEFINE_WAIT(wait);
- WARN_ON_ONCE(sqd && sqd->thread != current);
+ WARN_ON_ONCE(sqd && data_race(sqd->thread) != current);
if (!current->io_uring)
return;
--
2.43.0
