| Date | Thu, 17 Oct 2019 12:59:40 +0200 | From | Pavel Machek <> | Subject | Re: [PATCH 4.19 56/81] kernel/sysctl.c: do not override max_threads provided by userspace |
| |
Hi!
> From: Michal Hocko <mhocko@suse.com> > > commit b0f53dbc4bc4c371f38b14c391095a3bb8a0bb40 upstream. > > Partially revert 16db3d3f1170 ("kernel/sysctl.c: threads-max observe > limits") because the patch is causing a regression to any workload which > needs to override the auto-tuning of the limit provided by kernel. > > set_max_threads is implementing a boot time guesstimate to provide a > sensible limit of the concurrently running threads so that runaways will > not deplete all the memory. This is a good thing in general but there > are workloads which might need to increase this limit for an application > to run (reportedly WebSpher MQ is affected) and that is simply not > possible after the mentioned change. It is also very dubious to > override an admin decision by an estimation that doesn't have any direct > relation to correctness of the kernel operation. > > Fix this by dropping set_max_threads from sysctl_max_threads so any > value is accepted as long as it fits into MAX_THREADS which is important > to check because allowing more threads could break internal robust futex > restriction. While at it, do not use MIN_THREADS as the lower boundary > because it is also only a heuristic for automatic estimation and admin > might have a good reason to stop new threads to be created even when > below this limit.
Ok, why not, but I smell followup work could be done:
> @@ -2635,7 +2635,7 @@ int sysctl_max_threads(struct ctl_table > if (ret || !write) > return ret; > > - set_max_threads(threads); > + max_threads = threads; >
AFAICT set_max_threads can now become __init.
Plus, I don't see any locking here, should this be WRITE_ONCE() at minimum?
Best regards, Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html [unhandled content-type:application/pgp-signature] |