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Subject[RFC GIT PULL] scheduler fix for autogroups
Linus,

Please [RFC] pull the latest sched-urgent-for-linus git tree
from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-urgent-for-linus

HEAD: 5258f386ea4e8454bc801fb443e8a4217da1947c sched/autogroup: Fix crash on reboot when autogroup is disabled

Larger and scarier than what I'd like to have so I marked it
[RFC], but the autogroup fix looks important enough - it's
enabled in a number of distros.

[ The other reason for the RFC: unfortunately the new feature
flag change "sched: Add WAKEUP_PREEMPTION feature flag, on by
default" got added weeks ago and got stuck below the autogroup
fix - I can rebase and untangle it if it's a problem. (It is
not expected to cause any change in behavior or problems.) ]

Thanks,

Ingo

------------------>
Ingo Molnar (1):
sched: Add WAKEUP_PREEMPTION feature flag, on by default

Mike Galbraith (1):
sched/autogroup: Fix crash on reboot when autogroup is disabled


fs/proc/base.c | 78 -----------------------------------------------
kernel/sched/auto_group.c | 68 +++++++----------------------------------
kernel/sched/auto_group.h | 9 +-----
kernel/sched/fair.c | 2 +-
kernel/sched/features.h | 5 +++
kernel/sysctl.c | 6 ++--
6 files changed, 20 insertions(+), 148 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 1b6c84c..bb1d962 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1271,81 +1271,6 @@ static const struct file_operations proc_pid_sched_operations = {

#endif

-#ifdef CONFIG_SCHED_AUTOGROUP
-/*
- * Print out autogroup related information:
- */
-static int sched_autogroup_show(struct seq_file *m, void *v)
-{
- struct inode *inode = m->private;
- struct task_struct *p;
-
- p = get_proc_task(inode);
- if (!p)
- return -ESRCH;
- proc_sched_autogroup_show_task(p, m);
-
- put_task_struct(p);
-
- return 0;
-}
-
-static ssize_t
-sched_autogroup_write(struct file *file, const char __user *buf,
- size_t count, loff_t *offset)
-{
- struct inode *inode = file->f_path.dentry->d_inode;
- struct task_struct *p;
- char buffer[PROC_NUMBUF];
- int nice;
- int err;
-
- memset(buffer, 0, sizeof(buffer));
- if (count > sizeof(buffer) - 1)
- count = sizeof(buffer) - 1;
- if (copy_from_user(buffer, buf, count))
- return -EFAULT;
-
- err = kstrtoint(strstrip(buffer), 0, &nice);
- if (err < 0)
- return err;
-
- p = get_proc_task(inode);
- if (!p)
- return -ESRCH;
-
- err = proc_sched_autogroup_set_nice(p, nice);
- if (err)
- count = err;
-
- put_task_struct(p);
-
- return count;
-}
-
-static int sched_autogroup_open(struct inode *inode, struct file *filp)
-{
- int ret;
-
- ret = single_open(filp, sched_autogroup_show, NULL);
- if (!ret) {
- struct seq_file *m = filp->private_data;
-
- m->private = inode;
- }
- return ret;
-}
-
-static const struct file_operations proc_pid_sched_autogroup_operations = {
- .open = sched_autogroup_open,
- .read = seq_read,
- .write = sched_autogroup_write,
- .llseek = seq_lseek,
- .release = single_release,
-};
-
-#endif /* CONFIG_SCHED_AUTOGROUP */
-
static ssize_t comm_write(struct file *file, const char __user *buf,
size_t count, loff_t *offset)
{
@@ -3036,9 +2961,6 @@ static const struct pid_entry tgid_base_stuff[] = {
#ifdef CONFIG_SCHED_DEBUG
REG("sched", S_IRUGO|S_IWUSR, proc_pid_sched_operations),
#endif
-#ifdef CONFIG_SCHED_AUTOGROUP
- REG("autogroup", S_IRUGO|S_IWUSR, proc_pid_sched_autogroup_operations),
-#endif
REG("comm", S_IRUGO|S_IWUSR, proc_pid_set_comm_operations),
#ifdef CONFIG_HAVE_ARCH_TRACEHOOK
INF("syscall", S_IRUGO, proc_pid_syscall),
diff --git a/kernel/sched/auto_group.c b/kernel/sched/auto_group.c
index 0984a21..0f1bacb 100644
--- a/kernel/sched/auto_group.c
+++ b/kernel/sched/auto_group.c
@@ -110,6 +110,9 @@ out_fail:

bool task_wants_autogroup(struct task_struct *p, struct task_group *tg)
{
+ if (!sysctl_sched_autogroup_enabled)
+ return false;
+
if (tg != &root_task_group)
return false;

@@ -143,15 +146,11 @@ autogroup_move_group(struct task_struct *p, struct autogroup *ag)

p->signal->autogroup = autogroup_kref_get(ag);

- if (!ACCESS_ONCE(sysctl_sched_autogroup_enabled))
- goto out;
-
t = p;
do {
sched_move_task(t);
} while_each_thread(p, t);

-out:
unlock_task_sighand(p, &flags);
autogroup_kref_put(prev);
}
@@ -159,8 +158,11 @@ out:
/* Allocates GFP_KERNEL, cannot be called under any spinlock */
void sched_autogroup_create_attach(struct task_struct *p)
{
- struct autogroup *ag = autogroup_create();
+ struct autogroup *ag;

+ if (!sysctl_sched_autogroup_enabled)
+ return;
+ ag = autogroup_create();
autogroup_move_group(p, ag);
/* drop extra reference added by autogroup_create() */
autogroup_kref_put(ag);
@@ -176,11 +178,15 @@ EXPORT_SYMBOL(sched_autogroup_detach);

void sched_autogroup_fork(struct signal_struct *sig)
{
+ if (!sysctl_sched_autogroup_enabled)
+ return;
sig->autogroup = autogroup_task_get(current);
}

void sched_autogroup_exit(struct signal_struct *sig)
{
+ if (!sysctl_sched_autogroup_enabled)
+ return;
autogroup_kref_put(sig->autogroup);
}

@@ -193,58 +199,6 @@ static int __init setup_autogroup(char *str)

__setup("noautogroup", setup_autogroup);

-#ifdef CONFIG_PROC_FS
-
-int proc_sched_autogroup_set_nice(struct task_struct *p, int nice)
-{
- static unsigned long next = INITIAL_JIFFIES;
- struct autogroup *ag;
- int err;
-
- if (nice < -20 || nice > 19)
- return -EINVAL;
-
- err = security_task_setnice(current, nice);
- if (err)
- return err;
-
- if (nice < 0 && !can_nice(current, nice))
- return -EPERM;
-
- /* this is a heavy operation taking global locks.. */
- if (!capable(CAP_SYS_ADMIN) && time_before(jiffies, next))
- return -EAGAIN;
-
- next = HZ / 10 + jiffies;
- ag = autogroup_task_get(p);
-
- down_write(&ag->lock);
- err = sched_group_set_shares(ag->tg, prio_to_weight[nice + 20]);
- if (!err)
- ag->nice = nice;
- up_write(&ag->lock);
-
- autogroup_kref_put(ag);
-
- return err;
-}
-
-void proc_sched_autogroup_show_task(struct task_struct *p, struct seq_file *m)
-{
- struct autogroup *ag = autogroup_task_get(p);
-
- if (!task_group_is_autogroup(ag->tg))
- goto out;
-
- down_read(&ag->lock);
- seq_printf(m, "/autogroup-%ld nice %d\n", ag->id, ag->nice);
- up_read(&ag->lock);
-
-out:
- autogroup_kref_put(ag);
-}
-#endif /* CONFIG_PROC_FS */
-
#ifdef CONFIG_SCHED_DEBUG
int autogroup_path(struct task_group *tg, char *buf, int buflen)
{
diff --git a/kernel/sched/auto_group.h b/kernel/sched/auto_group.h
index 8bd0471..4552c6b 100644
--- a/kernel/sched/auto_group.h
+++ b/kernel/sched/auto_group.h
@@ -4,11 +4,6 @@
#include <linux/rwsem.h>

struct autogroup {
- /*
- * reference doesn't mean how many thread attach to this
- * autogroup now. It just stands for the number of task
- * could use this autogroup.
- */
struct kref kref;
struct task_group *tg;
struct rw_semaphore lock;
@@ -29,9 +24,7 @@ extern bool task_wants_autogroup(struct task_struct *p, struct task_group *tg);
static inline struct task_group *
autogroup_task_group(struct task_struct *p, struct task_group *tg)
{
- int enabled = ACCESS_ONCE(sysctl_sched_autogroup_enabled);
-
- if (enabled && task_wants_autogroup(p, tg))
+ if (task_wants_autogroup(p, tg))
return p->signal->autogroup->tg;

return tg;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6b800a1..f936552 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2907,7 +2907,7 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
* Batch and idle tasks do not preempt non-idle tasks (their preemption
* is driven by the tick):
*/
- if (unlikely(p->policy != SCHED_NORMAL))
+ if (unlikely(p->policy != SCHED_NORMAL) || !sched_feat(WAKEUP_PREEMPTION))
return;

find_matching_se(&se, &pse);
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index eebefca..e68e69a 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -32,6 +32,11 @@ SCHED_FEAT(LAST_BUDDY, true)
SCHED_FEAT(CACHE_HOT_BUDDY, true)

/*
+ * Allow wakeup-time preemption of the current task:
+ */
+SCHED_FEAT(WAKEUP_PREEMPTION, true)
+
+/*
* Use arch dependent cpu power functions
*/
SCHED_FEAT(ARCH_POWER, true)
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 81c7b1a..2914d0f 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -363,10 +363,8 @@ static struct ctl_table kern_table[] = {
.procname = "sched_autogroup_enabled",
.data = &sysctl_sched_autogroup_enabled,
.maxlen = sizeof(unsigned int),
- .mode = 0644,
- .proc_handler = proc_dointvec_minmax,
- .extra1 = &zero,
- .extra2 = &one,
+ .mode = 0444,
+ .proc_handler = proc_dointvec,
},
#endif
#ifdef CONFIG_CFS_BANDWIDTH

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