Messages in this thread | | | Date | Tue, 24 Feb 2015 22:31:03 +0100 | From | Heinrich Schuchardt <> | Subject | Re: [PATCH 3/3] kernel/sysctl.c: threads-max observe limits |
| |
On 24.02.2015 22:17, David Rientjes wrote: > 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.
threads_max is set to the value the user inputs if it is inside the interval [20, FUTEX_TID_MASK] and it is capped by the value calculated from totalram_pages.
So lowering and raising is still possible (inside the limits).
> >> 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", > Best regards
Heinrich
| |