diff options
| author | Ming Lei <tom.leiming@gmail.com> | 2026-05-13 18:19:40 +0800 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2026-05-13 07:55:39 -0600 |
| commit | 87d0740b7c4cc847be1b6f307ab6d8547cb1a726 (patch) | |
| tree | 373d52f4a7af345139e85ca14d669b4861417c29 | |
| parent | 836efd35c472d89c838d7b17ef339ddb3286ffc5 (diff) | |
selftests: ublk: cap nthreads to kernel's actual nr_hw_queues
dev->nthreads is derived from the user-requested queue count before the
ADD command, but the kernel may reduce nr_hw_queues (capped to
nr_cpu_ids). When the VM has fewer CPUs than requested queues, the
daemon creates more handler threads than there are kernel queues.
In non-batch mode, the extra threads access uninitialized queues
(q_depth=0), submit zero io_uring SQEs, and block forever in
io_cqring_wait. In batch mode, the extra threads cause similar hangs
during device removal.
In both cases, the stuck threads prevent the daemon from closing the
char device, holding the last ublk_device reference and causing
ublk_ctrl_del_dev() to hang in wait_event_interruptible().
Fix by capping dev->nthreads to the kernel-returned nr_hw_queues after
the ADD command completes. per_io_tasks mode is excluded because threads
interleave across all queues, so nthreads > nr_hw_queues is valid.
Fixes: abe54c160346 ("selftests: ublk: kublk: decouple ublk_queues from ublk server threads")
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Link: https://patch.msgid.link/20260513101941.1373998-1-tom.leiming@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
| -rw-r--r-- | tools/testing/selftests/ublk/kublk.c | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/tools/testing/selftests/ublk/kublk.c b/tools/testing/selftests/ublk/kublk.c index fbd9b1e7342a..0b23c09daea5 100644 --- a/tools/testing/selftests/ublk/kublk.c +++ b/tools/testing/selftests/ublk/kublk.c @@ -1735,6 +1735,17 @@ static int __cmd_dev_add(const struct dev_ctx *ctx) goto fail; } + /* + * The kernel may reduce nr_hw_queues (e.g. capped to nr_cpu_ids). + * Cap nthreads to the actual queue count to avoid creating extra + * handler threads that will hang during device removal. + * + * per_io_tasks mode is excluded: threads interleave across all + * queues so nthreads > nr_hw_queues is valid and intentional. + */ + if (!ctx->per_io_tasks && dev->nthreads > info->nr_hw_queues) + dev->nthreads = info->nr_hw_queues; + ret = ublk_start_daemon(ctx, dev); ublk_dbg(UBLK_DBG_DEV, "%s: daemon exit %d\n", __func__, ret); if (ret < 0) |