From: Ying Han <yinghan@xxxxxxxxxx>
It's pointless to kill a task if another thread sharing its mm cannot be
killed to allow future memory freeing. A subsequent patch will prevent
kills in such cases, but first it's necessary to have a way to flag a
task that shares memory with an OOM_DISABLE task that doesn't incur an
additional tasklist scan, which would make select_bad_process() an O(n^2)
function.
This patch adds an atomic counter to struct mm_struct that follows how
many threads attached to it have an oom_score_adj of OOM_SCORE_ADJ_MIN.
They cannot be killed by the kernel, so their memory cannot be freed in
oom conditions.
This only requires task_lock() on the task that we're operating on, it
does not require mm->mmap_sem since task_lock() pins the mm and the
operation is atomic.
[rientjes@xxxxxxxxxx: changelog and sys_unshare() code]
Signed-off-by: Ying Han <yinghan@xxxxxxxxxx>
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
fs/exec.c | 5 +++++
fs/proc/base.c | 30 ++++++++++++++++++++++++++++++
include/linux/mm_types.h | 2 ++
kernel/exit.c | 3 +++
kernel/fork.c | 13 ++++++++++++-
5 files changed, 52 insertions(+), 1 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -54,6 +54,7 @@
#include <linux/fsnotify.h>
#include <linux/fs_struct.h>
#include <linux/pipe_fs_i.h>
+#include <linux/oom.h>
#include <asm/uaccess.h>
#include <asm/mmu_context.h>
@@ -745,6 +746,10 @@ static int exec_mmap(struct mm_struct *mm)
tsk->mm = mm;
tsk->active_mm = mm;
activate_mm(active_mm, mm);
+ if (tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
+ atomic_dec(&active_mm->oom_disable_count);
+ atomic_inc(&tsk->mm->oom_disable_count);
+ }
task_unlock(tsk);
arch_pick_mmap_layout(mm);
if (old_mm) {
diff --git a/fs/proc/base.c b/fs/proc/base.c
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1047,6 +1047,21 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
return -EACCES;
}
+ task_lock(task);
+ if (!task->mm) {
+ task_unlock(task);
+ unlock_task_sighand(task, &flags);
+ put_task_struct(task);
+ return -EINVAL;
+ }
+
+ if (oom_adjust != task->signal->oom_adj) {
+ if (oom_adjust == OOM_DISABLE)
+ atomic_inc(&task->mm->oom_disable_count);
+ if (task->signal->oom_adj == OOM_DISABLE)
+ atomic_dec(&task->mm->oom_disable_count);
+ }
+
/*
* Warn that /proc/pid/oom_adj is deprecated, see
* Documentation/feature-removal-schedule.txt.
@@ -1065,6 +1080,7 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
else
task->signal->oom_score_adj = (oom_adjust * OOM_SCORE_ADJ_MAX) /
-OOM_DISABLE;
+ task_unlock(task);
unlock_task_sighand(task, &flags);
put_task_struct(task);
@@ -1133,6 +1149,19 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
return -EACCES;
}
+ task_lock(task);
+ if (!task->mm) {
+ task_unlock(task);
+ unlock_task_sighand(task, &flags);
+ put_task_struct(task);
+ return -EINVAL;
+ }
+ if (oom_score_adj != task->signal->oom_score_adj) {
+ if (oom_score_adj == OOM_SCORE_ADJ_MIN)
+ atomic_inc(&task->mm->oom_disable_count);
+ if (task->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
+ atomic_dec(&task->mm->oom_disable_count);
+ }
task->signal->oom_score_adj = oom_score_adj;
/*
* Scale /proc/pid/oom_adj appropriately ensuring that OOM_DISABLE is
@@ -1143,6 +1172,7 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
else
task->signal->oom_adj = (oom_score_adj * OOM_ADJUST_MAX) /
OOM_SCORE_ADJ_MAX;
+ task_unlock(task);
unlock_task_sighand(task, &flags);
put_task_struct(task);
return count;
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -310,6 +310,8 @@ struct mm_struct {
#ifdef CONFIG_MMU_NOTIFIER
struct mmu_notifier_mm *mmu_notifier_mm;
#endif
+ /* How many tasks sharing this mm are OOM_DISABLE */
+ atomic_t oom_disable_count;
};
/* Future-safe accessor for struct mm_struct's cpu_vm_mask. */
diff --git a/kernel/exit.c b/kernel/exit.c
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -50,6 +50,7 @@
#include <linux/perf_event.h>
#include <trace/events/sched.h>
#include <linux/hw_breakpoint.h>
+#include <linux/oom.h>
#include <asm/uaccess.h>
#include <asm/unistd.h>
@@ -689,6 +690,8 @@ static void exit_mm(struct task_struct * tsk)
enter_lazy_tlb(mm, current);
/* We don't want this task to be frozen prematurely */
clear_freeze_flag(tsk);
+ if (tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
+ atomic_dec(&mm->oom_disable_count);
task_unlock(tsk);
mm_update_next_owner(mm);
mmput(mm);
diff --git a/kernel/fork.c b/kernel/fork.c
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -65,6 +65,7 @@
#include <linux/perf_event.h>
#include <linux/posix-timers.h>
#include <linux/user-return-notifier.h>
+#include <linux/oom.h>
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
@@ -485,6 +486,7 @@ static struct mm_struct * mm_init(struct mm_struct * mm, struct task_struct *p)
mm->cached_hole_size = ~0UL;
mm_init_aio(mm);
mm_init_owner(mm, p);
+ atomic_set(&mm->oom_disable_count, 0);
if (likely(!mm_alloc_pgd(mm))) {
mm->def_flags = 0;
@@ -738,6 +740,8 @@ good_mm:
/* Initializing for Swap token stuff */
mm->token_priority = 0;
mm->last_interval = 0;
+ if (tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
+ atomic_inc(&mm->oom_disable_count);
tsk->mm = mm;
tsk->active_mm = mm;
@@ -1296,8 +1300,11 @@ bad_fork_cleanup_io:
bad_fork_cleanup_namespaces:
exit_task_namespaces(p);
bad_fork_cleanup_mm:
- if (p->mm)
+ if (p->mm) {
+ if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
+ atomic_dec(&p->mm->oom_disable_count);
mmput(p->mm);
+ }
bad_fork_cleanup_signal:
if (!(clone_flags & CLONE_THREAD))
free_signal_struct(p->signal);
@@ -1690,6 +1697,10 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
active_mm = current->active_mm;
current->mm = new_mm;
current->active_mm = new_mm;
+ if (current->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
+ atomic_dec(&mm->oom_disable_count);
+ atomic_inc(&new_mm->oom_disable_count);
+ }
activate_mm(active_mm, new_mm);
new_mm = mm;
}
--
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