On Thu, 28 Mar 2019 00:30:57 -0400 Kimberly Brown <[email protected]> wrote:
> On Thu, Mar 21, 2019 at 04:04:20PM +0000, Michael Kelley wrote: > > From: Kimberly Brown <[email protected]> Sent: Wednesday, March 20, > > 2019 8:48 PM > > > > > > Adding more locks will solve the problem but it seems like overkill. > > > > > > Why not either use a reference count or an RCU style access for the > > > > > > ring buffer? > > > > > > > > > > I agree that a reference count or RCU could also solve this problem. > > > > > Using mutex locks seemed like the most straightforward solution, but > > > > > I'll certainly switch to a different approach if it's better! > > > > > > > > > > Are you concerned about the extra memory required for the mutex locks, > > > > > read performance, or something else? > > > > > > > > Locks in control path are ok, but my concern is performance of the > > > > data path which puts packets in/out of rings. To keep reasonable > > > > performance, > > > > no additional locking should be added in those paths. > > > > > > > > So if data path is using RCU, can/should the control operations also > > > > use it? > > > > > > Hi Stephen, > > Do you have any additional questions or suggestions for this race > condition and the mutex locks? I think that your initial questions were > addressed in the responses below. If there's anything else, please let > me know! > > Thanks, > Kim > > > > > The data path doesn't use RCU to protect the ring buffers. > > > > My $.02: The mutex is obtained only in the sysfs path and the "delete > > ringbuffers" path, neither of which is performance or concurrency > > sensitive. > > There's no change to any path that reads or writes data from/to the ring > > buffers. It seems like the mutex is the most straightforward solution to > > preventing sysfs from accessing the ring buffer info while the memory is > > being freed as part of "delete ringbuffers". > > > > Michael I have no problems with the patch you did. My discussion was more around the general issues with ringbuffers being detached from the device. Not sure if it was even a good design choice but that is something that is hard to fix now.
