On Thu, Mar 21, 2019 at 04:04:20PM +0000, Michael Kelley wrote: > From: Kimberly Brown <kimbrow...@gmail.com> 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
