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:
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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>
>
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