Messages in this thread | | | Date | Fri, 9 Mar 2007 12:02:14 -0500 | From | "Dmitry Torokhov" <> | Subject | Re: refcounting drivers' data structures used in sysfs buffers |
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On 3/9/07, Oliver Neukum <oneukum@suse.de> wrote: > Am Freitag, 9. März 2007 17:32 schrieb Alan Stern: > > On Fri, 9 Mar 2007, Oliver Neukum wrote: > > > > > Am Donnerstag, 8. März 2007 17:02 schrieb Alan Stern: > > > > On Thu, 8 Mar 2007, Oliver Neukum wrote: > > > > > > > > > Hi, > > > > > > > > > > after a lightning bolt from high above I've been looking into refcounting > > > > > the data structures drivers use to provide the data used to refill sysfs > > > > > buffers. I've come to the following conclusion. > > > > > > > > > > 1. struct sysfs_buffer must have a struct kref * and probably a destructor > > > > > pointer > > > > > 2. drivers must be able to pass these pointers through an extended > > > > > device_create_file() > > > > > 3. Drivers must use refcounting if they want to use attributes > > > > > 4. read/write/poll must do refcounting > > > > > > > > > > I am not sure where to store the pointers. struct sysfs_dirent() looks > > > > > like the obvious choice. Comments? > > > > > > > > Can you explain the reasoning that led to these conclusions? And what > > > > exactly was your lightning bolt? > > > > > > The old race between disconnect and IO to attribute via sysfs again. > > > If I cannot disassociate the drivers from the buffers in the buffers, drivers > > > must not deallocate the data necessary to answer sysfs callbacks while > > > a buffer exists. > > > > Why wouldn't you be able to dissociate a driver from a buffer? That was > > the whole point of adding .orphan to sysfs_buffer and creating > > sysfs_buffer_collection -- it was supposed to solve exactly this race. > > It did solve the race but deadlocked when unbinding devices through sysfs. > Linux therefore asked for the patch to be reverted and wants the isue solved > with refcounting. >
I think we already have all refcounting that is needed. What is missing is subsystem-provided ->release() hooks for drivers to release driver-specific resources when a device finally goes away.
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