From: Jens Axboe axboe@kernel.dk
No direct upstream commit exists for this issue. It was fixed in 5.18 as part of a larger rework of the completion side.
io_commit_cqring() writes the CQ ring tail to make it visible, but it also kicks off any deferred work we have. A ring setup with IOPOLL does not need any locking around the CQ ring updates, as we're always under the ctx uring_lock. But if we have deferred work that needs processing, then io_queue_deferred() assumes that the completion_lock is held, as it is for !IOPOLL.
Add a lockdep assertion to check and document this fact, and have io_iopoll_complete() check if we have deferred work and run that separately with the appropriate lock grabbed.
Cc: stable@vger.kernel.org # 5.10, 5.15 Reported-by: dghost david daviduniverse18@gmail.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- io_uring/io_uring.c | 25 +++++++++++++++++++++---- 1 file changed, 21 insertions(+), 4 deletions(-)
--- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -1521,6 +1521,8 @@ static void io_kill_timeout(struct io_ki
static void io_queue_deferred(struct io_ring_ctx *ctx) { + lockdep_assert_held(&ctx->completion_lock); + while (!list_empty(&ctx->defer_list)) { struct io_defer_entry *de = list_first_entry(&ctx->defer_list, struct io_defer_entry, list); @@ -1572,14 +1574,24 @@ static void __io_commit_cqring_flush(str io_queue_deferred(ctx); }
-static inline void io_commit_cqring(struct io_ring_ctx *ctx) +static inline bool io_commit_needs_flush(struct io_ring_ctx *ctx) +{ + return ctx->off_timeout_used || ctx->drain_active; +} + +static inline void __io_commit_cqring(struct io_ring_ctx *ctx) { - if (unlikely(ctx->off_timeout_used || ctx->drain_active)) - __io_commit_cqring_flush(ctx); /* order cqe stores with ring update */ smp_store_release(&ctx->rings->cq.tail, ctx->cached_cq_tail); }
+static inline void io_commit_cqring(struct io_ring_ctx *ctx) +{ + if (unlikely(io_commit_needs_flush(ctx))) + __io_commit_cqring_flush(ctx); + __io_commit_cqring(ctx); +} + static inline bool io_sqring_full(struct io_ring_ctx *ctx) { struct io_rings *r = ctx->rings; @@ -2518,7 +2530,12 @@ static void io_iopoll_complete(struct io io_req_free_batch(&rb, req, &ctx->submit_state); }
- io_commit_cqring(ctx); + if (io_commit_needs_flush(ctx)) { + spin_lock(&ctx->completion_lock); + __io_commit_cqring_flush(ctx); + spin_unlock(&ctx->completion_lock); + } + __io_commit_cqring(ctx); io_cqring_ev_posted_iopoll(ctx); io_req_free_batch_finish(ctx, &rb); }