On Thu, Nov 29, 2018 at 04:35:12PM +1100, NeilBrown wrote: > On Wed, Nov 28 2018, J. Bruce Fields wrote: > > > On Wed, Nov 28, 2018 at 11:45:46AM +0300, Vasily Averin wrote: > >> Dear all, we have found memory leak on OpenVz7 node and believe it > >> affects mainline too. > >> > >> sunrpc_cache_lookup() removes exprired cache_head from hash, however > >> if it waits for reply on submitted cache_request both of them can leak > >> forever, nobody cleans unhashed cache_heads. > >> > >> Originally we had claim on busy loop device of stopped container, that > >> had executed nfs server inside. Device was kept by mount that was > >> detached from already destroyed mount namespace. By using crash > >> search we have found some structure with path struct related to our > >> mount. Finally we have found that it was alive svc_export struct used > >> by to alive cache_request, however both of them pointed to already > >> freed cache_detail. > >> > >> We decided that cache_detail was correctly freed during destroy of net > >> namespace, however svc_export with taken path struct, cache_request > >> and some other structures seems was leaked forever. > >> > >> This could happen only if cache_head of svc_export was removed from > >> hash on cache_detail before its destroy. Finally we have found that it > >> could happen when sunrpc_cache_lookup() removes expired cache_head > >> from hash. > >> > >> Usually it works correctly and cache_put(freeme) frees expired > >> cache_head. However in our case cache_head have an extra reference > >> counter from stalled cache_request. Becasue of cache_head was removed > >> from hash of cache_detail it cannot be found in cache_clean() and its > >> cache_request cannot be freed in cache_dequeue(). Memory leaks > >> forever, exactly like we observed. > >> > >> After may attempts we have reproduced this situation on OpenVz7 > >> kernel, however our reproducer is quite long and complex. > >> Unfortunately we still did not reproduced this problem on mainline > >> kernel and did not validated the patch yet. > >> > >> It would be great if someone advised us some simple way to trigger > >> described scenario. > > > > I think you should be able to produce hung upcalls by flushing the cache > > (exportfs -f), then stopping mountd, then trying to access the > > filesystem from a client. Does that help? > > > >> We are not sure that our patch is correct, please let us know if our > >> analyze missed something. > > > > It looks OK to me, but it would be helpful to have Neil's review too. > > Yes, it makes sense to me. > Reviewed-by: NeilBrown <neilb@xxxxxxxx> OK, applied for 4.21.--b.
