p->mm->oom_disable_count tracks how many threads sharing p->mm have an
oom_score_adj value of OOM_SCORE_ADJ_MIN, which disables the oom killer
for that task. If non-zero, p->mm->oom_disable_count indicates killing a
task sharing p->mm won't help since other threads cannot be killed and
the memory can't be freed.
oom_score_adj is a per-process value stored in p->signal->oom_score_adj,
which is protected by p->sighand->siglock. Thus, it's necessary to take
this lock whenever the value is tested.
This patch introduces the necessary locking to ensure oom_score_adj can
be tested and/or changed with consistency. This isn't the only locking
necessary to work with oom_score_adj: task_lock(p) must also be held or
the mm otherwise pinned in memory to ensure it doesn't change while
siglock is held. That locking is already in place.
Reported-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
v2: cleaned up locking and fixed lockdep warnings
For 2.6.37-rc-series.
fs/exec.c | 10 +++++++---
kernel/exit.c | 8 ++++++--
kernel/fork.c | 31 ++++++++++++++++++++++---------
3 files changed, 35 insertions(+), 14 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -741,6 +741,7 @@ static int exec_mmap(struct mm_struct *mm)
{
struct task_struct *tsk;
struct mm_struct * old_mm, *active_mm;
+ unsigned long flags;
/* Notify parent that we're no longer interested in the old VM */
tsk = current;
@@ -766,9 +767,12 @@ static int exec_mmap(struct mm_struct *mm)
tsk->mm = mm;
tsk->active_mm = mm;
activate_mm(active_mm, mm);
- if (old_mm && tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
- atomic_dec(&old_mm->oom_disable_count);
- atomic_inc(&tsk->mm->oom_disable_count);
+ if (lock_task_sighand(tsk, &flags)) {
+ if (old_mm && tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
+ atomic_dec(&old_mm->oom_disable_count);
+ atomic_inc(&tsk->mm->oom_disable_count);
+ }
+ unlock_task_sighand(tsk, &flags);
}
task_unlock(tsk);
arch_pick_mmap_layout(mm);
diff --git a/kernel/exit.c b/kernel/exit.c
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -644,6 +644,7 @@ static void exit_mm(struct task_struct * tsk)
{
struct mm_struct *mm = tsk->mm;
struct core_state *core_state;
+ unsigned long flags;
mm_release(tsk, mm);
if (!mm)
@@ -688,8 +689,11 @@ 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);
+ if (lock_task_sighand(tsk, &flags)) {
+ if (tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
+ atomic_dec(&mm->oom_disable_count);
+ unlock_task_sighand(tsk, &flags);
+ }
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
@@ -708,6 +708,7 @@ fail_nocontext:
static int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
{
struct mm_struct * mm, *oldmm;
+ unsigned long flags;
int retval;
tsk->min_flt = tsk->maj_flt = 0;
@@ -743,8 +744,11 @@ 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);
+ if (lock_task_sighand(tsk, &flags)) {
+ if (tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
+ atomic_inc(&mm->oom_disable_count);
+ unlock_task_sighand(tsk, &flags);
+ }
tsk->mm = mm;
tsk->active_mm = mm;
@@ -1306,10 +1310,13 @@ bad_fork_cleanup_namespaces:
exit_task_namespaces(p);
bad_fork_cleanup_mm:
if (p->mm) {
- task_lock(p);
- if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
- atomic_dec(&p->mm->oom_disable_count);
- task_unlock(p);
+ unsigned long flags;
+
+ if (lock_task_sighand(p, &flags)) {
+ if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
+ atomic_dec(&p->mm->oom_disable_count);
+ unlock_task_sighand(p, &flags);
+ }
mmput(p->mm);
}
bad_fork_cleanup_signal:
@@ -1700,13 +1707,19 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
}
if (new_mm) {
+ unsigned long flags;
+
mm = current->mm;
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);
+ if (lock_task_sighand(current, &flags)) {
+ if (current->signal->oom_score_adj ==
+ OOM_SCORE_ADJ_MIN) {
+ atomic_dec(&mm->oom_disable_count);
+ atomic_inc(&new_mm->oom_disable_count);
+ }
+ unlock_task_sighand(current, &flags);
}
activate_mm(active_mm, new_mm);
new_mm = mm;
--
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