Messages in this thread | | | Date | Tue, 24 Feb 2015 13:17:03 -0800 (PST) | From | David Rientjes <> | Subject | Re: [PATCH 3/3] kernel/sysctl.c: threads-max observe limits |
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On Tue, 24 Feb 2015, Heinrich Schuchardt wrote:
> Users can change the maximum number of threads by writing to > /proc/sys/kernel/threads-max. > > With the patch the value entered is checked against the same > limits that apply when fork_init is called. >
Correct me if I'm wrong, but this is a change in functionality (without update to Documentation/sysctl/kernel.txt which describes threads-max) since it does not allow the value to be lowered as before from the calculation involving totalram_pages. The value passed to set_max_threads() only caps the value.
> Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de> > --- > include/linux/sysctl.h | 3 +++ > kernel/fork.c | 24 ++++++++++++++++++++++++ > kernel/sysctl.c | 6 ++---- > 3 files changed, 29 insertions(+), 4 deletions(-) > > diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h > index b7361f8..795d5fe 100644 > --- a/include/linux/sysctl.h > +++ b/include/linux/sysctl.h > @@ -212,4 +212,7 @@ static inline void setup_sysctl_set(struct ctl_table_set *p, > > #endif /* CONFIG_SYSCTL */ > > +int sysctl_max_threads(struct ctl_table *table, int write, > + void __user *buffer, size_t *lenp, loff_t *ppos); > + > #endif /* _LINUX_SYSCTL_H */ > diff --git a/kernel/fork.c b/kernel/fork.c > index 880c78d..52a07c7 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -74,6 +74,7 @@ > #include <linux/uprobes.h> > #include <linux/aio.h> > #include <linux/compiler.h> > +#include <linux/sysctl.h> > > #include <asm/pgtable.h> > #include <asm/pgalloc.h> > @@ -2024,3 +2025,26 @@ int unshare_files(struct files_struct **displaced) > task_unlock(task); > return 0; > } > + > +int sysctl_max_threads(struct ctl_table *table, int write, > + void __user *buffer, size_t *lenp, loff_t *ppos) > +{ > + struct ctl_table t; > + int ret; > + int threads = max_threads; > + int min = MIN_THREADS; > + int max = MAX_THREADS; > + > + t = *table; > + t.data = &threads; > + t.extra1 = &min; > + t.extra2 = &max; > + > + ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos); > + if (ret || !write) > + return ret; > + > + set_max_threads(threads); > + > + return 0; > +} > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > index 137c7f6..2e195ae 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -92,11 +92,9 @@ > #include <linux/nmi.h> > #endif > > - > #if defined(CONFIG_SYSCTL) > > /* External variables not in a header file. */ > -extern int max_threads; > extern int suid_dumpable; > #ifdef CONFIG_COREDUMP > extern int core_uses_pid; > @@ -709,10 +707,10 @@ static struct ctl_table kern_table[] = { > #endif > { > .procname = "threads-max", > - .data = &max_threads, > + .data = NULL, > .maxlen = sizeof(int), > .mode = 0644, > - .proc_handler = proc_dointvec, > + .proc_handler = sysctl_max_threads, > }, > { > .procname = "random",
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