On Sat, 16 Mar 2019 21:49:28 -0400 Kimberly Brown <kimbrow...@gmail.com> wrote:
> On Thu, Mar 14, 2019 at 03:45:33PM -0700, Stephen Hemminger wrote: > > On Thu, 14 Mar 2019 13:05:15 -0700 > > "Kimberly Brown" <kimbrow...@gmail.com> wrote: > > > > > Fix a race condition that can result in a ring buffer pointer being set > > > to null while a "_show" function is reading the ring buffer's data. This > > > problem was discussed here: > > > https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.org > > > %2Flkml%2F2018%2F10%2F18%2F779&data=02%7C01%7Csthemmin%40microsoft.com > > > %7C1d7557d667b741bdbb6008d6a8b8620f%7C72f988bf86f141af91ab2d7cd011db47%7C1 > > > %7C0%7C636881907217609564&sdata=1bUbLaxsODANM7lCBR8lxyYajNpufuwUW%2FOl > > > vtGu2hU%3D&reserved=0 > > > > > > To fix the race condition, add a new mutex lock to the > > > "hv_ring_buffer_info" struct. Add a new function, > > > "hv_ringbuffer_pre_init()", where a channel's inbound and outbound > > > ring_buffer_info mutex locks are initialized. > > > > > > ... snip ... > > > > 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?