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io_uring: ensure IOPOLL locks around deferred work

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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>
This commit is contained in:
Jens Axboe 2023-07-11 09:35:30 -06:00 committed by Greg Kroah-Hartman
parent 4909d0ad17
commit fb348857e7
1 changed files with 21 additions and 4 deletions
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25
io_uring/io_uring.c
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@ -1524,6 +1524,8 @@ static void io_kill_timeout(struct io_kiocb *req, int status)
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);
@ -1575,14 +1577,24 @@ static void __io_commit_cqring_flush(struct io_ring_ctx *ctx)
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;
@ -2521,7 +2533,12 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
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);
}