From: Michal Hocko <mhocko@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>,
"Eric W. Biederman" <ebiederm@xmission.com>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: threads-max observe limits
Date: Mon, 23 Sep 2019 10:08:08 +0200 [thread overview]
Message-ID: <20190923080808.GA6016@dhcp22.suse.cz> (raw)
In-Reply-To: <875zlk3tz9.fsf@x220.int.ebiederm.org>
Andrew, do you want me to send the patch or you can grab it from here?
On Sun 22-09-19 16:24:10, Eric W. Biederman wrote:
> Michal Hocko <mhocko@kernel.org> writes:
>
> > From 711000fdc243b6bc68a92f9ef0017ae495086d39 Mon Sep 17 00:00:00 2001
> > From: Michal Hocko <mhocko@suse.com>
> > Date: Sun, 22 Sep 2019 08:45:28 +0200
> > Subject: [PATCH] kernel/sysctl.c: do not override max_threads provided by
> > userspace
> >
> > 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.
> >
> > Fixes: 16db3d3f1170 ("kernel/sysctl.c: threads-max observe limits")
> > Cc: stable
> > Signed-off-by: Michal Hocko <mhocko@suse.com>
> Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com>
Thanks Eric.
> > ---
> > kernel/fork.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/fork.c b/kernel/fork.c
> > index 2852d0e76ea3..ef865be37e98 100644
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -2929,7 +2929,7 @@ int sysctl_max_threads(struct ctl_table *table, int write,
> > struct ctl_table t;
> > int ret;
> > int threads = max_threads;
> > - int min = MIN_THREADS;
> > + int min = 1;
> > int max = MAX_THREADS;
> >
> > t = *table;
> > @@ -2941,7 +2941,7 @@ int sysctl_max_threads(struct ctl_table *table, int write,
> > if (ret || !write)
> > return ret;
> >
> > - set_max_threads(threads);
> > + max_threads = threads;
> >
> > return 0;
> > }
> > --
> > 2.20.1
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2019-09-23 8:08 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-17 10:03 threads-max observe limits Michal Hocko
2019-09-17 15:28 ` Heinrich Schuchardt
2019-09-17 15:38 ` Michal Hocko
2019-09-17 17:26 ` Eric W. Biederman
2019-09-18 7:15 ` Michal Hocko
2019-09-19 7:59 ` Michal Hocko
2019-09-19 19:38 ` Andrew Morton
2019-09-19 19:33 ` Eric W. Biederman
2019-09-22 6:58 ` Michal Hocko
2019-09-22 15:31 ` Heinrich Schuchardt
2019-09-22 21:40 ` Eric W. Biederman
2019-09-22 21:24 ` Eric W. Biederman
2019-09-23 8:08 ` Michal Hocko [this message]
2019-09-23 21:23 ` Eric W. Biederman
2019-09-24 8:48 ` Michal Hocko
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