Am 24.08.2018 um 15:01 schrieb Michal Hocko: > On Fri 24-08-18 14:52:26, Christian König wrote: >> Am 24.08.2018 um 14:33 schrieb Michal Hocko: > [...] >>> Thiking about it some more, I can imagine that a notifier callback which >>> performs an allocation might trigger a memory reclaim and that in turn >>> might trigger a notifier to be invoked and recurse. But notifier >>> shouldn't really allocate memory. They are called from deep MM code >>> paths and this would be extremely deadlock prone. Maybe Jerome can come >>> up some more realistic scenario. If not then I would propose to simplify >>> the locking here. We have lockdep to catch self deadlocks and it is >>> always better to handle a specific issue rather than having a code >>> without a clear indication how it can recurse. >> Well I agree that we should probably fix that, but I have some concerns to >> remove the existing workaround. >> >> See we added that to get rid of a real problem in a customer environment and >> I don't want to that to show up again. > It would really help to know more about that case and fix it properly > rather than workaround it like this. Anyway, let me think how to handle > the non-blocking notifier invocation then. I was not able to come up > with anything remotely sane yet. With avoiding allocating memory in the write lock path I don't see an issue any more with that. All what the write lock path does now is adding items to a linked lists, arrays etc.... So there is no more blocking involved here and the read lock side should be able to grab the lock immediately. Christian.
