linux-kernel - [PATCH] ublk: clean up user copy references on ublk server exit

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Message-ID: <20251213001950.2103303-1-csander@purestorage.com>
Date: Fri, 12 Dec 2025 17:19:49 -0700
From: Caleb Sander Mateos <csander@...estorage.com>
To: Ming Lei <ming.lei@...hat.com>,
	Jens Axboe <axboe@...nel.dk>
Cc: Uday Shankar <ushankar@...estorage.com>,
	Caleb Sander Mateos <csander@...estorage.com>,
	linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] ublk: clean up user copy references on ublk server exit

If a ublk server process releases a ublk char device file, any requests
dispatched to the ublk server but not yet completed will retain a ref
value of UBLK_REFCOUNT_INIT. Before commit e63d2228ef83 ("ublk: simplify
aborting ublk request"), __ublk_fail_req() would decrement the reference
count before completing the failed request. However, that commit
optimized __ublk_fail_req() to call __ublk_complete_rq() directly
without decrementing the request reference count.
The leaked reference count incorrectly allows user copy and zero copy
operations on the completed ublk request. It also triggers the
WARN_ON_ONCE(refcount_read(&io->ref)) warnings in ublk_queue_reinit()
and ublk_deinit_queue().
Commit c5c5eb24ed61 ("ublk: avoid ublk_io_release() called after ublk
char dev is closed") already fixed the issue for ublk devices using
UBLK_F_SUPPORT_ZERO_COPY or UBLK_F_AUTO_BUF_REG. However, the reference
count leak also affects UBLK_F_USER_COPY, the other reference-counted
data copy mode. Fix the condition in ublk_check_and_reset_active_ref()
to include all reference-counted data copy modes. This ensures that any
ublk requests still owned by the ublk server when it exits have their
reference counts reset to 0.

Signed-off-by: Caleb Sander Mateos <csander@...estorage.com>
Fixes: e63d2228ef83 ("ublk: simplify aborting ublk request")
---
 drivers/block/ublk_drv.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index df9831783a13..78f3e22151b9 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -1581,12 +1581,11 @@ static void ublk_set_canceling(struct ublk_device *ub, bool canceling)

 static bool ublk_check_and_reset_active_ref(struct ublk_device *ub)
 {
 	int i, j;

-	if (!(ub->dev_info.flags & (UBLK_F_SUPPORT_ZERO_COPY |
-					UBLK_F_AUTO_BUF_REG)))
+	if (!ublk_dev_need_req_ref(ub))
 		return false;

 	for (i = 0; i < ub->dev_info.nr_hw_queues; i++) {
 		struct ublk_queue *ubq = ublk_get_queue(ub, i);

-- 
2.45.2