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authorLennart Poettering <lennart@poettering.net>2009-06-15 17:17:47 +0200
committerIngo Molnar <mingo@elte.hu>2009-06-15 17:31:59 +0200
commitca94c442535a44d508c99a77e54f21a59f4fc462 (patch)
tree5dda78242ed00f035e033ebd1f29200303b92b10 /include/linux/sched.h
parent45e3e1935e2857c54783291107d33323b3ef33c8 (diff)
sched: Introduce SCHED_RESET_ON_FORK scheduling policy flag
This patch introduces a new flag SCHED_RESET_ON_FORK which can be passed to the kernel via sched_setscheduler(), ORed in the policy parameter. If set this will make sure that when the process forks a) the scheduling priority is reset to DEFAULT_PRIO if it was higher and b) the scheduling policy is reset to SCHED_NORMAL if it was either SCHED_FIFO or SCHED_RR. Why have this? Currently, if a process is real-time scheduled this will 'leak' to all its child processes. For security reasons it is often (always?) a good idea to make sure that if a process acquires RT scheduling this is confined to this process and only this process. More specifically this makes the per-process resource limit RLIMIT_RTTIME useful for security purposes, because it makes it impossible to use a fork bomb to circumvent the per-process RLIMIT_RTTIME accounting. This feature is also useful for tools like 'renice' which can then change the nice level of a process without having this spill to all its child processes. Why expose this via sched_setscheduler() and not other syscalls such as prctl() or sched_setparam()? prctl() does not take a pid parameter. Due to that it would be impossible to modify this flag for other processes than the current one. The struct passed to sched_setparam() can unfortunately not be extended without breaking compatibility, since sched_setparam() lacks a size parameter. How to use this from userspace? In your RT program simply replace this: sched_setscheduler(pid, SCHED_FIFO, &param); by this: sched_setscheduler(pid, SCHED_FIFO|SCHED_RESET_ON_FORK, &param); Signed-off-by: Lennart Poettering <lennart@poettering.net> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <20090615152714.GA29092@tango.0pointer.de> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'include/linux/sched.h')
-rw-r--r--include/linux/sched.h6
1 files changed, 6 insertions, 0 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4896fdfec91..d4a2c6662f7 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -38,6 +38,8 @@
#define SCHED_BATCH 3
/* SCHED_ISO: reserved but not implemented yet */
#define SCHED_IDLE 5
+/* Can be ORed in to make sure the process is reverted back to SCHED_NORMAL on fork */
+#define SCHED_RESET_ON_FORK 0x40000000
#ifdef __KERNEL__
@@ -1209,6 +1211,10 @@ struct task_struct {
unsigned did_exec:1;
unsigned in_execve:1; /* Tell the LSMs that the process is doing an
* execve */
+
+ /* Revert to default priority/policy when forking */
+ unsigned sched_reset_on_fork:1;
+
pid_t pid;
pid_t tgid;