Hmm,I guess I might already understand the problem. Consider such situation,during storage_probe,we set timeout_handler,and we submit an urb, then we go to sleep.If time out occurs,timeout_handler is called, at this moment, storage_probe should still be in sleeping status, so timeout_handler couldn't go sleep, otherwise the whole driver would not work any more.This can explain the question I raised before.Thanks.
Regards Jason On 7/11/07, Oliver Neukum <[EMAIL PROTECTED]> wrote: > Am Mittwoch, 11. Juli 2007 schrieb jidong xiao: > > On 7/11/07, Oliver Neukum <[EMAIL PROTECTED]> wrote: > > > Am Mittwoch, 11. Juli 2007 schrieb jidong xiao: > > > > I see there are two routines, usb_unlink_urb and usb_kill_urb,the > > > > latter one should be used for sync unlinking,this means it can go to > > > > sleep,it won't return until the completion handler have finished.And > > > > the former one could not go to sleep.But what's difference between > > > > sync and async,I mean,why do we need such two kinds of mechanism to > > > > cancel a transfer request? > > > > > > Under some conditions, eg. network drivers' and the storage driver's > > > timeout handling, drivers cannot sleep. They have to stop transfers > > > asynchronously. > > > > Ok,let's talk about the timeout handling routine,we defined a > > timeout_handler in drivers/usb/storage/transport.c,inside that > > function,we will call usb_unlink_urb,why cannot we sleep?what impact > > if the driver go to sleep here? > > The handler is called with a spinlock held. If you sleep and another > task tries to take the same lock, you will get a deadlock. This is the > general reason for being unable to sleep in USB drivers. > > Regards > Oliver > ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
