On Fri, 27 Aug 2010, Andrew Morton wrote:
> > 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.
>
> I don't think lockdep likes us taking task_lock() inside
> lock_task_sighand(), in oom_adjust_write():
>
> [ 78.185341]
> [ 78.185341] =========================================================
> [ 78.185341] [ INFO: possible irq lock inversion dependency detected ]
> [ 78.185341] 2.6.36-rc2-mm1 #6
> [ 78.185341] ---------------------------------------------------------
> [ 78.185341] kworker/0:1/0 just changed the state of lock:
> [ 78.185341] (&(&sighand->siglock)->rlock){-.....}, at: [<ffffffff81042d83>] lock_task_sighand+0x9a/0xda
> [ 78.185341] but this lock took another, HARDIRQ-unsafe lock in the past:
> [ 78.185341] (&(&p->alloc_lock)->rlock){+.+...}
> [ 78.185341]
> [ 78.185341] and interrupts could create inverse lock ordering between them.
oom: fix locking for oom_adj and oom_score_adj
The locking order in oom_adjust_write() and oom_score_adj_write() for
task->alloc_lock and task->sighand->siglock is reversed, and lockdep
notices that irqs could encounter an ABBA scenario.
This fixes the locking order so that we always take task_lock(task) prior
to lock_task_sighand(task).
Reported-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
Can't be folded into the offending patch,
oom-add-per-mm-oom-disable-count.patch, because later patch
oom-rewrite-error-handling-for-oom_adj-and-oom_score_adj-tunables.patch
rewrites error handling in these functions.
fs/proc/base.c | 40 +++++++++++++++++++++-------------------
1 files changed, 21 insertions(+), 19 deletions(-)
diff --git a/fs/proc/base.c b/fs/proc/base.c
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1042,9 +1042,16 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
err = -ESRCH;
goto out;
}
+
+ task_lock(task);
+ if (!task->mm) {
+ err = -EINVAL;
+ goto err_task_lock;
+ }
+
if (!lock_task_sighand(task, &flags)) {
err = -ESRCH;
- goto err_task_struct;
+ goto err_task_lock;
}
if (oom_adjust < task->signal->oom_adj && !capable(CAP_SYS_RESOURCE)) {
@@ -1052,12 +1059,6 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
goto err_sighand;
}
- task_lock(task);
- if (!task->mm) {
- err = -EINVAL;
- goto err_task_lock;
- }
-
if (oom_adjust != task->signal->oom_adj) {
if (oom_adjust == OOM_DISABLE)
atomic_inc(&task->mm->oom_disable_count);
@@ -1083,11 +1084,10 @@ 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;
-err_task_lock:
- task_unlock(task);
err_sighand:
unlock_task_sighand(task, &flags);
-err_task_struct:
+err_task_lock:
+ task_unlock(task);
put_task_struct(task);
out:
return err < 0 ? err : count;
@@ -1150,21 +1150,24 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
err = -ESRCH;
goto out;
}
+
+ task_lock(task);
+ if (!task->mm) {
+ err = -EINVAL;
+ goto err_task_lock;
+ }
+
if (!lock_task_sighand(task, &flags)) {
err = -ESRCH;
- goto err_task_struct;
+ goto err_task_lock;
}
+
if (oom_score_adj < task->signal->oom_score_adj &&
!capable(CAP_SYS_RESOURCE)) {
err = -EACCES;
goto err_sighand;
}
- task_lock(task);
- if (!task->mm) {
- err = -EINVAL;
- goto err_task_lock;
- }
if (oom_score_adj != task->signal->oom_score_adj) {
if (oom_score_adj == OOM_SCORE_ADJ_MIN)
atomic_inc(&task->mm->oom_disable_count);
@@ -1181,11 +1184,10 @@ 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;
-err_task_lock:
- task_unlock(task);
err_sighand:
unlock_task_sighand(task, &flags);
-err_task_struct:
+err_task_lock:
+ task_unlock(task);
put_task_struct(task);
out:
return err < 0 ? err : count;
--
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