On 2 December 2016 at 10:29, Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> wrote:
> handle_cmd_completion() frees a command structure which might
> be still referenced by xhci->current_cmd. This might cause
> problem when xhci->current_cmd is accessed after that.
>
> A real-life case could be like this. The host takes a very long
> time to respond to a command, and the command timer is fired at
> the same time when the command completion event arrives. The
> command completion handler frees xhci->current_cmd before the
> timer function can grab xhci->lock. Afterward, timer function
> grabs the lock and go ahead with checking and setting members
> of xhci->current_cmd.
>
> Cc: <stable@xxxxxxxxxxxxxxx> # v3.16+
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
Nice catch. I was also curious where set xhci->current_cmd to be NULL
when current command is freed.
Tested-by: Baolin Wang <baolin.wang@xxxxxxxxxx>
> ---
> drivers/usb/host/xhci-ring.c | 16 +++++++++++-----
> 1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
> index bdf6b13..13e05f6 100644
> --- a/drivers/usb/host/xhci-ring.c
> +++ b/drivers/usb/host/xhci-ring.c
> @@ -1267,14 +1267,16 @@ void xhci_handle_command_timeout(unsigned long data)
> bool second_timeout = false;
> xhci = (struct xhci_hcd *) data;
>
> - /* mark this command to be cancelled */
> spin_lock_irqsave(&xhci->lock, flags);
> - if (xhci->current_cmd) {
> - if (xhci->current_cmd->status == COMP_CMD_ABORT)
> - second_timeout = true;
> - xhci->current_cmd->status = COMP_CMD_ABORT;
> + if (!xhci->current_cmd) {
> + spin_unlock_irqrestore(&xhci->lock, flags);
> + return;
> }
>
> + if (xhci->current_cmd->status == COMP_CMD_ABORT)
> + second_timeout = true;
> + xhci->current_cmd->status = COMP_CMD_ABORT;
> +
> /* Make sure command ring is running before aborting it */
> hw_ring_state = xhci_read_64(xhci, &xhci->op_regs->cmd_ring);
> if ((xhci->cmd_ring_state & CMD_RING_STATE_RUNNING) &&
> @@ -1422,6 +1424,10 @@ static void handle_cmd_completion(struct xhci_hcd *xhci,
> xhci->current_cmd = list_entry(cmd->cmd_list.next,
> struct xhci_command, cmd_list);
> mod_timer(&xhci->cmd_timer, jiffies + XHCI_CMD_DEFAULT_TIMEOUT);
> + } else if (xhci->current_cmd == cmd) {
> + xhci->current_cmd = NULL;
> + } else {
> + xhci_warn(xhci, "WARN current_cmd doesn't match command\n");
> }
>
> event_handled:
> --
> 2.1.4
>
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--
Baolin.wang
Best Regards
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