Re: [REGRESSION 6.17-rc3] usb/xhci: possible memory leak after suspend/resume cycle.

["Michał Pecio" <michal.pecio@gmail.com>]

On Sat, 30 Aug 2025 02:13:54 +0800, David Wang wrote:
> Hi,
>
> I have been watching kernel memory usage for drivers for a while, via /proc/allocinfo.
> After upgrade to 6.17-rc3, I notice memory usage behavior changes for usb drivers:
> 
> Before rc3, after several suspend/resume cycles, usb devices's memory usage is very stable:
> 
>        40960        5 drivers/usb/host/xhci-mem.c:980 [xhci_hcd] func:xhci_alloc_virt_device 9
>         1024        1 drivers/usb/host/xhci-mem.c:841 [xhci_hcd] func:xhci_alloc_tt_info 2
>          320       10 drivers/usb/host/xhci-mem.c:461 [xhci_hcd] func:xhci_alloc_container_ctx 31
>         1920       15 drivers/usb/host/xhci-mem.c:377 [xhci_hcd] func:xhci_ring_alloc 31
>          112       12 drivers/usb/host/xhci-mem.c:49 [xhci_hcd] func:xhci_segment_alloc 32
>         1792       28 drivers/usb/host/xhci-mem.c:38 [xhci_hcd] func:xhci_segment_alloc 59
> 
> But with rc3, the memory usage increase after each suspend/resume cycle: 
> 
> #1:
>        49152        6 drivers/usb/host/xhci-mem.c:980 [xhci_hcd] func:xhci_alloc_virt_device 9
>         1024        1 drivers/usb/host/xhci-mem.c:841 [xhci_hcd] func:xhci_alloc_tt_info 2
>          384       12 drivers/usb/host/xhci-mem.c:461 [xhci_hcd] func:xhci_alloc_container_ctx 32
>         2176       17 drivers/usb/host/xhci-mem.c:377 [xhci_hcd] func:xhci_ring_alloc 32
>          128       14 drivers/usb/host/xhci-mem.c:49 [xhci_hcd] func:xhci_segment_alloc 34
>         2048       32 drivers/usb/host/xhci-mem.c:38 [xhci_hcd] func:xhci_segment_alloc 61
> #2:
>        57344        7 drivers/usb/host/xhci-mem.c:980 [xhci_hcd] func:xhci_alloc_virt_device 13
>         1024        1 drivers/usb/host/xhci-mem.c:841 [xhci_hcd] func:xhci_alloc_tt_info 3
>          448       14 drivers/usb/host/xhci-mem.c:461 [xhci_hcd] func:xhci_alloc_container_ctx 46
>         2432       19 drivers/usb/host/xhci-mem.c:377 [xhci_hcd] func:xhci_ring_alloc 43
>          144       16 drivers/usb/host/xhci-mem.c:49 [xhci_hcd] func:xhci_segment_alloc 44
>         2304       36 drivers/usb/host/xhci-mem.c:38 [xhci_hcd] func:xhci_segment_alloc 82
> #3:
>        65536        8 drivers/usb/host/xhci-mem.c:980 [xhci_hcd] func:xhci_alloc_virt_device 17
>         1024        1 drivers/usb/host/xhci-mem.c:841 [xhci_hcd] func:xhci_alloc_tt_info 4
>          512       16 drivers/usb/host/xhci-mem.c:461 [xhci_hcd] func:xhci_alloc_container_ctx 60
>         2688       21 drivers/usb/host/xhci-mem.c:377 [xhci_hcd] func:xhci_ring_alloc 54
>          160       18 drivers/usb/host/xhci-mem.c:49 [xhci_hcd] func:xhci_segment_alloc 54
>         2560       40 drivers/usb/host/xhci-mem.c:38 [xhci_hcd] func:xhci_segment_alloc 103
> 
> The memory increasing pattern keeps going on for each suspend/resume afterwards, I am not
> sure whether those memory would be released sometime later.
> 
> And in kernel log, two lines of error always showed up after suspend/resume:
> 
> 	[  295.613598] xhci_hcd 0000:03:00.0: dma_pool_destroy xHCI ring segments busy
> 	[  295.613605] xhci_hcd 0000:03:00.0: dma_pool_destroy xHCI input/output contexts busy

Hi,

Good work, looks like suspend/resume is a little understested corner
of this driver.

Did you check whether the same leak occurs if you simply disconnect
a device or if it's truly unique to suspend?

> And bisect narrow down to commit 2eb03376151bb8585caa23ed2673583107bb5193(
> "usb: xhci: Fix slot_id resource race conflict"):

I see a trivial bug which everyone (myself included tbh) missed before.
Does this help?

diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index f11e13f9cdb4..f294032c2ad7 100644
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -932,7 +932,7 @@ void xhci_free_virt_device(struct xhci_hcd *xhci, struct xhci_virt_device *dev,
  */
 static void xhci_free_virt_devices_depth_first(struct xhci_hcd *xhci, int slot_id)
 {
-	struct xhci_virt_device *vdev;
+	struct xhci_virt_device *vdev, *tmp_vdev;
 	struct list_head *tt_list_head;
 	struct xhci_tt_bw_info *tt_info, *next;
 	int i;
@@ -952,8 +952,8 @@ static void xhci_free_virt_devices_depth_first(struct xhci_hcd *xhci, int slot_i
 		if (tt_info->slot_id == slot_id) {
 			/* are any devices using this tt_info? */
 			for (i = 1; i < HCS_MAX_SLOTS(xhci->hcs_params1); i++) {
-				vdev = xhci->devs[i];
-				if (vdev && (vdev->tt_info == tt_info))
+				tmp_vdev = xhci->devs[i];
+				if (tmp_vdev && (tmp_vdev->tt_info == tt_info))
 					xhci_free_virt_devices_depth_first(
 						xhci, i);
 			}