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Subject[mmotm][PATCH 1/4] oom: move oom_adj value from task_struct to signal_struct
Date
Currently, OOM logic callflow is here.

__out_of_memory()
select_bad_process() for each task
badness() calculate badness of one task
oom_kill_process() search child
oom_kill_task() kill target task and mm shared tasks with it

example, process-A have two thread, thread-A and thread-B and it
have very fat memory and each thread have following oom_adj and oom_score.

thread-A: oom_adj = OOM_DISABLE, oom_score = 0
thread-B: oom_adj = 0, oom_score = very-high

Then, select_bad_process() select thread-B, but oom_kill_task() refuse
kill the task because thread-A have OOM_DISABLE.
Thus __out_of_memory() call select_bad_process() again. but select_bad_process()
select the same task. It mean kernel fall in livelock.

The fact is, select_bad_process() must select killable task. otherwise
OOM logic go into livelock.

And root cause is, oom_adj shouldn't be per-thread value. it should be
per-process value because OOM-killer kill a process, not thread. Thus
This patch moves oomkilladj (now more appropriately named oom_adj) from
struct task_struct to struct signal_struct. it naturally prevent
select_bad_process() choose wrong task.

Cc: Paul Menage <menage@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
---
fs/proc/base.c | 24 ++++++++++++++++++++----
include/linux/sched.h | 3 ++-
kernel/fork.c | 2 ++
mm/oom_kill.c | 34 +++++++++++++++-------------------
4 files changed, 39 insertions(+), 24 deletions(-)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 5856219..fbf8788 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1000,11 +1000,17 @@ static ssize_t oom_adjust_read(struct file *file, char __user *buf,
struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
char buffer[PROC_NUMBUF];
size_t len;
- int oom_adjust;
+ int oom_adjust = OOM_DISABLE;
+ unsigned long flags;

if (!task)
return -ESRCH;
- oom_adjust = task->oomkilladj;
+
+ if (lock_task_sighand(task, &flags)) {
+ oom_adjust = task->signal->oom_adj;
+ unlock_task_sighand(task, &flags);
+ }
+
put_task_struct(task);

len = snprintf(buffer, sizeof(buffer), "%i\n", oom_adjust);
@@ -1018,6 +1024,7 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
struct task_struct *task;
char buffer[PROC_NUMBUF], *end;
int oom_adjust;
+ unsigned long flags;

memset(buffer, 0, sizeof(buffer));
if (count > sizeof(buffer) - 1)
@@ -1033,11 +1040,20 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
task = get_proc_task(file->f_path.dentry->d_inode);
if (!task)
return -ESRCH;
- if (oom_adjust < task->oomkilladj && !capable(CAP_SYS_RESOURCE)) {
+ if (!lock_task_sighand(task, &flags)) {
+ put_task_struct(task);
+ return -ESRCH;
+ }
+
+ if (oom_adjust < task->signal->oom_adj && !capable(CAP_SYS_RESOURCE)) {
+ unlock_task_sighand(task, &flags);
put_task_struct(task);
return -EACCES;
}
- task->oomkilladj = oom_adjust;
+
+ task->signal->oom_adj = oom_adjust;
+
+ unlock_task_sighand(task, &flags);
put_task_struct(task);
if (end - buffer == 0)
return -EIO;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index c40fb84..3a2ef73 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -678,6 +678,8 @@ struct signal_struct {
unsigned audit_tty;
struct tty_audit_buf *tty_audit_buf;
#endif
+
+ int oom_adj; /* OOM kill score adjustment (bit shift) */
};

/* Context switch must be unlocked if interrupts are to be enabled */
@@ -1246,7 +1248,6 @@ struct task_struct {
* a short time
*/
unsigned char fpu_counter;
- s8 oomkilladj; /* OOM kill score adjustment (bit shift). */
#ifdef CONFIG_BLK_DEV_IO_TRACE
unsigned int btrace_seq;
#endif
diff --git a/kernel/fork.c b/kernel/fork.c
index c755101..58cd45a 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -904,6 +904,8 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)

tty_audit_fork(sig);

+ sig->oom_adj = current->signal->oom_adj;
+
return 0;
}

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index a7b2460..55dcadd 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -58,6 +58,10 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
unsigned long points, cpu_time, run_time;
struct mm_struct *mm;
struct task_struct *child;
+ int oom_adj = p->signal->oom_adj;
+
+ if (oom_adj == OOM_DISABLE)
+ return 0;

task_lock(p);
mm = p->mm;
@@ -148,15 +152,15 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
points /= 8;

/*
- * Adjust the score by oomkilladj.
+ * Adjust the score by oom_adj.
*/
- if (p->oomkilladj) {
- if (p->oomkilladj > 0) {
+ if (oom_adj) {
+ if (oom_adj > 0) {
if (!points)
points = 1;
- points <<= p->oomkilladj;
+ points <<= oom_adj;
} else
- points >>= -(p->oomkilladj);
+ points >>= -(oom_adj);
}

#ifdef DEBUG
@@ -251,7 +255,7 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
*ppoints = ULONG_MAX;
}

- if (p->oomkilladj == OOM_DISABLE)
+ if (p->signal->oom_adj == OOM_DISABLE)
continue;

points = badness(p, uptime.tv_sec);
@@ -304,7 +308,7 @@ static void dump_tasks(const struct mem_cgroup *mem)
}
printk(KERN_INFO "[%5d] %5d %5d %8lu %8lu %3d %3d %s\n",
p->pid, __task_cred(p)->uid, p->tgid, mm->total_vm,
- get_mm_rss(mm), (int)task_cpu(p), p->oomkilladj,
+ get_mm_rss(mm), (int)task_cpu(p), p->signal->oom_adj,
p->comm);
task_unlock(p);
} while_each_thread(g, p);
@@ -359,18 +363,9 @@ static int oom_kill_task(struct task_struct *p)
* change to NULL at any time since we do not hold task_lock(p).
* However, this is of no concern to us.
*/
-
- if (mm == NULL)
+ if (!mm || p->signal->oom_adj == OOM_DISABLE)
return 1;

- /*
- * Don't kill the process if any threads are set to OOM_DISABLE
- */
- do_each_thread(g, q) {
- if (q->mm == mm && q->oomkilladj == OOM_DISABLE)
- return 1;
- } while_each_thread(g, q);
-
__oom_kill_task(p, 1);

/*
@@ -394,8 +389,9 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,

if (printk_ratelimit()) {
printk(KERN_WARNING "%s invoked oom-killer: "
- "gfp_mask=0x%x, order=%d, oomkilladj=%d\n",
- current->comm, gfp_mask, order, current->oomkilladj);
+ "gfp_mask=0x%x, order=%d, oom_adj=%d\n",
+ current->comm, gfp_mask, order,
+ current->signal->oom_adj);
task_lock(current);
cpuset_print_task_mems_allowed(current);
task_unlock(current);
--
1.6.2.5




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