io_uring: further limit non-owner defer-tw cq waiting

In case of DEFER_TASK_WORK we try to restrict waiters to only one task,
which is also the only submitter; however, we don't do it reliably,
which might be very confusing and backfire in the future. E.g. we
currently allow multiple tasks in io_iopoll_check().

Fixes: c0e0d6ba25f1 ("io_uring: add IORING_SETUP_DEFER_TASKRUN")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/94c83c0a7fe468260ee2ec31bdb0095d6e874ba2.1662652536.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index b5245c5d102ca66fa74a536e88120098ae36b869..e95877398b57ab348fbae02d462ba1eab4ff90ee 100644 (file)
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -1398,6 +1398,9 @@ static int io_iopoll_check(struct io_ring_ctx *ctx, long min)
        int ret = 0;
        unsigned long check_cq;
 
+       if (!io_allowed_run_tw(ctx))
+               return -EEXIST;
+
        check_cq = READ_ONCE(ctx->check_cq);
        if (unlikely(check_cq)) {
                if (check_cq & BIT(IO_CHECK_CQ_OVERFLOW_BIT))
@@ -2382,6 +2385,9 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
        ktime_t timeout = KTIME_MAX;
        int ret;
 
+       if (!io_allowed_run_tw(ctx))
+               return -EEXIST;
+
        do {
                /* always run at least 1 task work to process local work */
                ret = io_run_task_work_ctx(ctx);

diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index 9d89425292b72ca502457033f6e8d08283ddc096..4eea0836170e4706ab0788603dde6d7c560565b6 100644 (file)
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -329,4 +329,15 @@ static inline struct io_kiocb *io_alloc_req(struct io_ring_ctx *ctx)
        return container_of(node, struct io_kiocb, comp_list);
 }
 
+static inline bool io_allowed_run_tw(struct io_ring_ctx *ctx)
+{
+       if (!(ctx->flags & IORING_SETUP_DEFER_TASKRUN))
+               return true;
+       if (unlikely(ctx->submitter_task != current)) {
+               /* maybe this is before any submissions */
+               return !ctx->submitter_task;
+       }
+       return true;
+}
+
 #endif