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proc, oom: drop bogus sighand lock

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Oleg has pointed out that can simplify both oom_adj_{read,write} and
oom_score_adj_{read,write} even further and drop the sighand lock.  The
main purpose of the lock was to protect p->signal from going away but this
will not happen since ea6d290ca3 ("signals: make task_struct->signal
immutable/refcountable").

The other role of the lock was to synchronize different writers,
especially those with CAP_SYS_RESOURCE.  Introduce a mutex for this
purpose.  Later patches will need this lock anyway.

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Link: http://lkml.kernel.org/r/1466426628-15074-3-git-send-email-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Michal Hocko 2016-07-28 15:44:37 -07:00 committed by Linus Torvalds
parent d49fbf766d
commit f913da596a
1 changed files with 17 additions and 34 deletions
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51
fs/proc/base.c
View File

@ -1024,23 +1024,21 @@ static ssize_t oom_adj_read(struct file *file, char __user *buf, size_t count,
char buffer[PROC_NUMBUF];
int oom_adj = OOM_ADJUST_MIN;
size_t len;
unsigned long flags;
if (!task)
return -ESRCH;
if (lock_task_sighand(task, &flags)) {
if (task->signal->oom_score_adj == OOM_SCORE_ADJ_MAX)
oom_adj = OOM_ADJUST_MAX;
else
oom_adj = (task->signal->oom_score_adj * -OOM_DISABLE) /
OOM_SCORE_ADJ_MAX;
unlock_task_sighand(task, &flags);
}
if (task->signal->oom_score_adj == OOM_SCORE_ADJ_MAX)
oom_adj = OOM_ADJUST_MAX;
else
oom_adj = (task->signal->oom_score_adj * -OOM_DISABLE) /
OOM_SCORE_ADJ_MAX;
put_task_struct(task);
len = snprintf(buffer, sizeof(buffer), "%d\n", oom_adj);
return simple_read_from_buffer(buf, count, ppos, buffer, len);
}
static DEFINE_MUTEX(oom_adj_mutex);
/*
* /proc/pid/oom_adj exists solely for backwards compatibility with previous
* kernels. The effective policy is defined by oom_score_adj, which has a
@ -1057,7 +1055,6 @@ static ssize_t oom_adj_write(struct file *file, const char __user *buf,
struct task_struct *task;
char buffer[PROC_NUMBUF];
int oom_adj;
unsigned long flags;
int err;
memset(buffer, 0, sizeof(buffer));
@ -1083,11 +1080,6 @@ static ssize_t oom_adj_write(struct file *file, const char __user *buf,
goto out;
}
if (!lock_task_sighand(task, &flags)) {
err = -ESRCH;
goto err_put_task;
}
/*
* Scale /proc/pid/oom_score_adj appropriately ensuring that a maximum
* value is always attainable.
@ -1097,10 +1089,11 @@ static ssize_t oom_adj_write(struct file *file, const char __user *buf,
else
oom_adj = (oom_adj * OOM_SCORE_ADJ_MAX) / -OOM_DISABLE;
mutex_lock(&oom_adj_mutex);
if (oom_adj < task->signal->oom_score_adj &&
!capable(CAP_SYS_RESOURCE)) {
err = -EACCES;
goto err_sighand;
goto err_unlock;
}
/*
@ -1113,9 +1106,8 @@ static ssize_t oom_adj_write(struct file *file, const char __user *buf,
task->signal->oom_score_adj = oom_adj;
trace_oom_score_adj_update(task);
err_sighand:
unlock_task_sighand(task, &flags);
err_put_task:
err_unlock:
mutex_unlock(&oom_adj_mutex);
put_task_struct(task);
out:
return err < 0 ? err : count;
@ -1133,15 +1125,11 @@ static ssize_t oom_score_adj_read(struct file *file, char __user *buf,
struct task_struct *task = get_proc_task(file_inode(file));
char buffer[PROC_NUMBUF];
short oom_score_adj = OOM_SCORE_ADJ_MIN;
unsigned long flags;
size_t len;
if (!task)
return -ESRCH;
if (lock_task_sighand(task, &flags)) {
oom_score_adj = task->signal->oom_score_adj;
unlock_task_sighand(task, &flags);
}
oom_score_adj = task->signal->oom_score_adj;
put_task_struct(task);
len = snprintf(buffer, sizeof(buffer), "%hd\n", oom_score_adj);
return simple_read_from_buffer(buf, count, ppos, buffer, len);
@ -1152,7 +1140,6 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
{
struct task_struct *task;
char buffer[PROC_NUMBUF];
unsigned long flags;
int oom_score_adj;
int err;
@ -1179,25 +1166,21 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
goto out;
}
if (!lock_task_sighand(task, &flags)) {
err = -ESRCH;
goto err_put_task;
}
mutex_lock(&oom_adj_mutex);
if ((short)oom_score_adj < task->signal->oom_score_adj_min &&
!capable(CAP_SYS_RESOURCE)) {
err = -EACCES;
goto err_sighand;
goto err_unlock;
}
task->signal->oom_score_adj = (short)oom_score_adj;
if (has_capability_noaudit(current, CAP_SYS_RESOURCE))
task->signal->oom_score_adj_min = (short)oom_score_adj;
trace_oom_score_adj_update(task);
err_sighand:
unlock_task_sighand(task, &flags);
err_put_task:
err_unlock:
mutex_unlock(&oom_adj_mutex);
put_task_struct(task);
out:
return err < 0 ? err : count;