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ublk: avoid ublk_io_release() called after ublk char dev is closed

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When running test_stress_04.sh, the following warning is triggered:

WARNING: CPU: 1 PID: 135 at drivers/block/ublk_drv.c:1933 ublk_ch_release+0x423/0x4b0 [ublk_drv]

This happens when the daemon is abruptly killed:

- some references may still be held, because registering IO buffer
doesn't grab ublk char device reference

OR

- io->task_registered_buffers won't be cleared because io buffer is
released from non-daemon context

For zero-copy and auto buffer register modes, I/O reference crosses
syscalls, so IO reference may not be dropped naturally when ublk server is
killed abruptly. However, when releasing io_uring context, it is guaranteed
that the reference is dropped finally, see io_sqe_buffers_unregister() from
io_ring_ctx_free().

Fix this by adding ublk_drain_io_references() that:
- Waits for active I/O references dropped in async way by scheduling
  work function, for avoiding ublk dev and io_uring file's release
  dependency
- Reinitializes io->ref and io->task_registered_buffers to clean state

This ensures the reference count state is clean when ublk_queue_reinit()
is called, preventing the warning and potential use-after-free.

Fixes: 1f6540e2aa ("ublk: zc register/unregister bvec")
Fixes: 1ceeedb597 ("ublk: optimize UBLK_IO_UNREGISTER_IO_BUF on daemon task")
Fixes: 8a8fe42d76 ("ublk: optimize UBLK_IO_REGISTER_IO_BUF on daemon task")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250827121602.2619736-2-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2025-08-27 20:15:59 +08:00 • committed by Jens Axboe
parent e3ef9445cd
commit c5c5eb24ed
1 changed files with 70 additions and 2 deletions
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72
drivers/block/ublk_drv.c
View file

@ -239,6 +239,7 @@ struct ublk_device {
struct mutex cancel_mutex;
bool canceling;
pid_t ublksrv_tgid;
struct delayed_work exit_work;
};
/* header of ublk_params */
@ -1595,12 +1596,62 @@ static void ublk_set_canceling(struct ublk_device *ub, bool canceling)
ublk_get_queue(ub, i)->canceling = canceling;
}
static int ublk_ch_release(struct inode *inode, struct file *filp)
static bool ublk_check_and_reset_active_ref(struct ublk_device *ub)
{
struct ublk_device *ub = filp->private_data;
int i, j;
if (!(ub->dev_info.flags & (UBLK_F_SUPPORT_ZERO_COPY |
UBLK_F_AUTO_BUF_REG)))
return false;
for (i = 0; i < ub->dev_info.nr_hw_queues; i++) {
struct ublk_queue *ubq = ublk_get_queue(ub, i);
for (j = 0; j < ubq->q_depth; j++) {
struct ublk_io *io = &ubq->ios[j];
unsigned int refs = refcount_read(&io->ref) +
io->task_registered_buffers;
/*
* UBLK_REFCOUNT_INIT or zero means no active
* reference
*/
if (refs != UBLK_REFCOUNT_INIT && refs != 0)
return true;
/* reset to zero if the io hasn't active references */
refcount_set(&io->ref, 0);
io->task_registered_buffers = 0;
}
}
return false;
}
static void ublk_ch_release_work_fn(struct work_struct *work)
{
struct ublk_device *ub =
container_of(work, struct ublk_device, exit_work.work);
struct gendisk *disk;
int i;
/*
* For zero-copy and auto buffer register modes, I/O references
* might not be dropped naturally when the daemon is killed, but
* io_uring guarantees that registered bvec kernel buffers are
* unregistered finally when freeing io_uring context, then the
* active references are dropped.
*
* Wait until active references are dropped for avoiding use-after-free
*
* registered buffer may be unregistered in io_ring's release hander,
* so have to wait by scheduling work function for avoiding the two
* file release dependency.
*/
if (ublk_check_and_reset_active_ref(ub)) {
schedule_delayed_work(&ub->exit_work, 1);
return;
}
/*
* disk isn't attached yet, either device isn't live, or it has
* been removed already, so we needn't to do anything
@ -1673,6 +1724,23 @@ unlock:
ublk_reset_ch_dev(ub);
out:
clear_bit(UB_STATE_OPEN, &ub->state);
/* put the reference grabbed in ublk_ch_release() */
ublk_put_device(ub);
}
static int ublk_ch_release(struct inode *inode, struct file *filp)
{
struct ublk_device *ub = filp->private_data;
/*
* Grab ublk device reference, so it won't be gone until we are
* really released from work function.
*/
ublk_get_device(ub);
INIT_DELAYED_WORK(&ub->exit_work, ublk_ch_release_work_fn);
schedule_delayed_work(&ub->exit_work, 0);
return 0;
}