From: Jens Axboe <axboe@xxxxxxxxx>
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@xxxxxxxxxxxxxxx # 5.10, 5.15
Reported-by: dghost david <daviduniverse18@xxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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);
}
