Re: [PATCH] ACPI hotplug: Fix panic on eject to ejected device

[Toshi Kani <toshi.kani@hp.com>]

On Wed, 2014-02-05 at 22:49 +0100, Rafael J. Wysocki wrote:
> On Wednesday, February 05, 2014 08:52:49 AM Toshi Kani wrote:
> > On Wed, 2014-02-05 at 11:05 +0000, Rafael J. Wysocki wrote:
> > > On Tuesday, February 04, 2014 05:48:28 PM Toshi Kani wrote:
> > > > When an eject request is sent to an ejected ACPI device, the following
> > > > panic occurs:
> > > > 
> > > >  ACPI: \_SB_.SCK3.CPU3: ACPI_NOTIFY_EJECT_REQUEST event
> > > >  BUG: unable to handle kernel NULL pointer dereference at 0000000000000070
> > > >  IP: [<ffffffff813a7cfe>] acpi_device_hotplug+0x10b/0x33b
> > > > 	:
> > > >  Call Trace:
> > > >  [<ffffffff813a24da>] acpi_hotplug_work_fn+0x1c/0x27
> > > >  [<ffffffff8109cbe5>] process_one_work+0x175/0x430
> > > >  [<ffffffff8109d7db>] worker_thread+0x11b/0x3a0
> > > > 
> > > > This is becase device->handler is NULL in acpi_device_hotplug().
> > > > This case was used to fail in acpi_hotplug_notify_cb() as the target
> > > > had no acpi_deivce.  However, acpi_device now exists after ejection.
> > > > 
> > > > Added a check to verify if acpi_device->handler is valid for an
> > > > eject request in acpi_hotplug_notify_cb().  Note that handler passed
> > > > from an argument is still valid while acpi_device->handler is NULL.
> > > > 
> > > > Signed-off-by: Toshi Kani <toshi.kani@hp.com>
> > > > ---
> > > >  drivers/acpi/scan.c |    5 +++--
> > > >  1 file changed, 3 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> > > > index 7384158..5cf6adf 100644
> > > > --- a/drivers/acpi/scan.c
> > > > +++ b/drivers/acpi/scan.c
> > > > @@ -484,7 +484,6 @@ static void acpi_device_hotplug(void *data, u32 src)
> > > >  static void acpi_hotplug_notify_cb(acpi_handle handle, u32 type, void *data)
> > > >  {
> > > >  	u32 ost_code = ACPI_OST_SC_NON_SPECIFIC_FAILURE;
> > > > -	struct acpi_scan_handler *handler = data;
> > > >  	struct acpi_device *adev;
> > > >  	acpi_status status;
> > > >  
> > > > @@ -500,7 +499,9 @@ static void acpi_hotplug_notify_cb(acpi_handle handle, u32 type, void *data)
> > > >  		break;
> > > >  	case ACPI_NOTIFY_EJECT_REQUEST:
> > > >  		acpi_handle_debug(handle, "ACPI_NOTIFY_EJECT_REQUEST event\n");
> > > > -		if (!handler->hotplug.enabled) {
> > > > +		if (!adev->handler)
> > > > +			goto err_out;
> > > > +		if (!adev->handler->hotplug.enabled) {
> > > >  			acpi_handle_err(handle, "Eject disabled\n");
> > > >  			ost_code = ACPI_OST_SC_EJECT_NOT_SUPPORTED;
> > > >  			goto err_out;
> > > 
> > > OK, I'll queue this up for the next pull request, but it actually isn't safe,
> > > because adev is not really guaranteed to exist here (it might have been deleted
> > > already when this function is running).
> > 
> > It should be safe since acpi_bus_get_device() fails in this function
> > when adev does not exist. 
> 
> Unfortunately, the object pointed to by adev may very well cease to exist after
> the acpi_bus_get_device() has returned and before the subsequent dereference of
> adev.

I see.  Thanks for the clarification.

-Toshi