This is a note to let you know that I've just added the patch titled

UAS: fix deadlock in error handling and PM flushing work

to my usb git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From f6cc6093a729ede1ff5658b493237c42b82ba107 Mon Sep 17 00:00:00 2001

From: Oliver Neukum oneukum@suse.com Date: Wed, 15 Apr 2020 16:17:50 +0200 Subject: UAS: fix deadlock in error handling and PM flushing work

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(-)

diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c index 08503e3507bf..d592071119ba 100644 --- a/drivers/usb/storage/uas.c +++ b/drivers/usb/storage/uas.c @@ -81,6 +81,19 @@ static void uas_free_streams(struct uas_dev_info *devinfo); 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 = @@ -109,7 +122,7 @@ static void uas_do_work(struct work_struct *work) 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); @@ -134,7 +147,7 @@ static void uas_add_work(struct uas_cmd_info *cmdinfo)

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) @@ -1229,7 +1242,31 @@ 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_IMPORT_NS(USB_STORAGE);