On 2 December 2016 at 12:40, Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> wrote:
> Hi,
>
> On 12/02/2016 12:18 PM, Baolin Wang wrote:
>> 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.
>
> Below code does:
Yes, I just means you did that, but the original code did not. Sorry
for confusing.
>
> 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");
> }
>
>
> Best regards,
> Lu Baolu
>
>> 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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