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From: Oleg Nesterov on 30 Mar 2010 13:50
->siglock is no longer needed to access task->signal, change
oom_adjust_read() and oom_adjust_write() to read/write oom_adj
lockless.

Yes, this means that "echo 2 >oom_adj" and "echo 1 >oom_adj"
can race and the second write can win, but I hope this is OK.

Also, cleanup the EACCES case a bit.

Signed-off-by: Oleg Nesterov <oleg(a)redhat.com>
---

fs/proc/base.c | 28 ++++++----------------------
1 file changed, 6 insertions(+), 22 deletions(-)

--- 34-rc1/fs/proc/base.c~PROC_5_OOM_ADJ 2010-03-30 18:23:50.000000000 +0200
+++ 34-rc1/fs/proc/base.c 2010-03-30 19:14:43.000000000 +0200
@@ -981,22 +981,16 @@ static ssize_t oom_adjust_read(struct fi
{
struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
char buffer[PROC_NUMBUF];
+ int oom_adjust;
size_t len;
- int oom_adjust = OOM_DISABLE;
- unsigned long flags;

if (!task)
return -ESRCH;

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

len = snprintf(buffer, sizeof(buffer), "%i\n", oom_adjust);
-
return simple_read_from_buffer(buf, count, ppos, buffer, len);
}

@@ -1006,7 +1000,6 @@ static ssize_t oom_adjust_write(struct f
struct task_struct *task;
char buffer[PROC_NUMBUF];
long oom_adjust;
- unsigned long flags;
int err;

memset(buffer, 0, sizeof(buffer));
@@ -1025,20 +1018,11 @@ static ssize_t oom_adjust_write(struct f
task = get_proc_task(file->f_path.dentry->d_inode);
if (!task)
return -ESRCH;
- 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->signal->oom_adj = oom_adjust;
-
- unlock_task_sighand(task, &flags);
+ if (task->signal->oom_adj <= oom_adjust || capable(CAP_SYS_RESOURCE))
+ task->signal->oom_adj = oom_adjust;
+ else
+ count = -EACCES;
put_task_struct(task);

return count;

--
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Prev: [PATCH] increase PREEMPT_BITS to 12 to avoid overflow when starting KVM
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