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    Subject[PATCH 4.9 57/80] UAS: fix deadlock in error handling and PM flushing work
    Date
    From: Oliver Neukum <oneukum@suse.com>

    commit f6cc6093a729ede1ff5658b493237c42b82ba107 upstream.

    A SCSI error handler and block runtime PM must not allocate
    memory with GFP_KERNEL. Furthermore they must not wait for
    tasks allocating memory with GFP_KERNEL.
    That means that they cannot share a workqueue with arbitrary tasks.

    Fix this for UAS using a private workqueue.

    Signed-off-by: Oliver Neukum <oneukum@suse.com>
    Fixes: f9dc024a2da1f ("uas: pre_reset and suspend: Fix a few races")
    Cc: stable <stable@vger.kernel.org>
    Link: https://lore.kernel.org/r/20200415141750.811-2-oneukum@suse.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/usb/storage/uas.c | 43 ++++++++++++++++++++++++++++++++++++++++---
    1 file changed, 40 insertions(+), 3 deletions(-)

    --- a/drivers/usb/storage/uas.c
    +++ b/drivers/usb/storage/uas.c
    @@ -82,6 +82,19 @@ static void uas_free_streams(struct uas_
    static void uas_log_cmd_state(struct scsi_cmnd *cmnd, const char *prefix,
    int status);

    +/*
    + * This driver needs its own workqueue, as we need to control memory allocation.
    + *
    + * In the course of error handling and power management uas_wait_for_pending_cmnds()
    + * needs to flush pending work items. In these contexts we cannot allocate memory
    + * by doing block IO as we would deadlock. For the same reason we cannot wait
    + * for anything allocating memory not heeding these constraints.
    + *
    + * So we have to control all work items that can be on the workqueue we flush.
    + * Hence we cannot share a queue and need our own.
    + */
    +static struct workqueue_struct *workqueue;
    +
    static void uas_do_work(struct work_struct *work)
    {
    struct uas_dev_info *devinfo =
    @@ -110,7 +123,7 @@ static void uas_do_work(struct work_stru
    if (!err)
    cmdinfo->state &= ~IS_IN_WORK_LIST;
    else
    - schedule_work(&devinfo->work);
    + queue_work(workqueue, &devinfo->work);
    }
    out:
    spin_unlock_irqrestore(&devinfo->lock, flags);
    @@ -135,7 +148,7 @@ static void uas_add_work(struct uas_cmd_

    lockdep_assert_held(&devinfo->lock);
    cmdinfo->state |= IS_IN_WORK_LIST;
    - schedule_work(&devinfo->work);
    + queue_work(workqueue, &devinfo->work);
    }

    static void uas_zap_pending(struct uas_dev_info *devinfo, int result)
    @@ -1236,7 +1249,31 @@ static struct usb_driver uas_driver = {
    .id_table = uas_usb_ids,
    };

    -module_usb_driver(uas_driver);
    +static int __init uas_init(void)
    +{
    + int rv;
    +
    + workqueue = alloc_workqueue("uas", WQ_MEM_RECLAIM, 0);
    + if (!workqueue)
    + return -ENOMEM;
    +
    + rv = usb_register(&uas_driver);
    + if (rv) {
    + destroy_workqueue(workqueue);
    + return -ENOMEM;
    + }
    +
    + return 0;
    +}
    +
    +static void __exit uas_exit(void)
    +{
    + usb_deregister(&uas_driver);
    + destroy_workqueue(workqueue);
    +}
    +
    +module_init(uas_init);
    +module_exit(uas_exit);

    MODULE_LICENSE("GPL");
    MODULE_AUTHOR(

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