From: Weitao Wang WeitaoWang-oc@zhaoxin.com
commit 26c6c2f8a907c9e3a2f24990552a4d77235791e6 upstream.
Usb core introduce the mechanism of giveback of URB in tasklet context to reduce hardware interrupt handling time. On some test situation(such as FIO with 4KB block size), when tasklet callback function called to giveback URB, interrupt handler add URB node to the bh->head list also. If check bh->head list again after finish all URB giveback of local_list, then it may introduce a "dynamic balance" between giveback URB and add URB to bh->head list. This tasklet callback function may not exit for a long time, which will cause other tasklet function calls to be delayed. Some real-time applications(such as KB and Mouse) will see noticeable lag.
In order to prevent the tasklet function from occupying the cpu for a long time at a time, new URBS will not be added to the local_list even though the bh->head list is not empty. But also need to ensure the left URB giveback to be processed in time, so add a member high_prio for structure giveback_urb_bh to prioritize tasklet and schelule this tasklet again if bh->head list is not empty.
At the same time, we are able to prioritize tasklet through structure member high_prio. So, replace the local high_prio_bh variable with this structure member in usb_hcd_giveback_urb.
Fixes: 94dfd7edfd5c ("USB: HCD: support giveback of URB in tasklet context") Cc: stable stable@kernel.org Reviewed-by: Alan Stern stern@rowland.harvard.edu Signed-off-by: Weitao Wang WeitaoWang-oc@zhaoxin.com Link: https://lore.kernel.org/r/20220726074918.5114-1-WeitaoWang-oc@zhaoxin.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/usb/core/hcd.c | 26 +++++++++++++++----------- include/linux/usb/hcd.h | 1 + 2 files changed, 16 insertions(+), 11 deletions(-)
--- a/drivers/usb/core/hcd.c +++ b/drivers/usb/core/hcd.c @@ -1814,7 +1814,6 @@ static void usb_giveback_urb_bh(unsigned
spin_lock_irq(&bh->lock); bh->running = true; - restart: list_replace_init(&bh->head, &local_list); spin_unlock_irq(&bh->lock);
@@ -1828,10 +1827,17 @@ static void usb_giveback_urb_bh(unsigned bh->completing_ep = NULL; }
- /* check if there are new URBs to giveback */ + /* + * giveback new URBs next time to prevent this function + * from not exiting for a long time. + */ spin_lock_irq(&bh->lock); - if (!list_empty(&bh->head)) - goto restart; + if (!list_empty(&bh->head)) { + if (bh->high_prio) + tasklet_hi_schedule(&bh->bh); + else + tasklet_schedule(&bh->bh); + } bh->running = false; spin_unlock_irq(&bh->lock); } @@ -1856,7 +1862,7 @@ static void usb_giveback_urb_bh(unsigned void usb_hcd_giveback_urb(struct usb_hcd *hcd, struct urb *urb, int status) { struct giveback_urb_bh *bh; - bool running, high_prio_bh; + bool running;
/* pass status to tasklet via unlinked */ if (likely(!urb->unlinked)) @@ -1867,13 +1873,10 @@ void usb_hcd_giveback_urb(struct usb_hcd return; }
- if (usb_pipeisoc(urb->pipe) || usb_pipeint(urb->pipe)) { + if (usb_pipeisoc(urb->pipe) || usb_pipeint(urb->pipe)) bh = &hcd->high_prio_bh; - high_prio_bh = true; - } else { + else bh = &hcd->low_prio_bh; - high_prio_bh = false; - }
spin_lock(&bh->lock); list_add_tail(&urb->urb_list, &bh->head); @@ -1882,7 +1885,7 @@ void usb_hcd_giveback_urb(struct usb_hcd
if (running) ; - else if (high_prio_bh) + else if (bh->high_prio) tasklet_hi_schedule(&bh->bh); else tasklet_schedule(&bh->bh); @@ -2900,6 +2903,7 @@ int usb_add_hcd(struct usb_hcd *hcd,
/* initialize tasklets */ init_giveback_urb_bh(&hcd->high_prio_bh); + hcd->high_prio_bh.high_prio = true; init_giveback_urb_bh(&hcd->low_prio_bh);
/* enable irqs just before we start the controller, --- a/include/linux/usb/hcd.h +++ b/include/linux/usb/hcd.h @@ -65,6 +65,7 @@
struct giveback_urb_bh { bool running; + bool high_prio; spinlock_t lock; struct list_head head; struct tasklet_struct bh;