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Michal Hockotorvalds
Michal Hocko
authored and
torvalds
committed
proc, oom: drop bogus sighand lock
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 ea6d290 ("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>
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‎fs/proc/base.c

Lines changed: 17 additions & 34 deletions
Original file line numberDiff line numberDiff line change
@@ -1024,23 +1024,21 @@ static ssize_t oom_adj_read(struct file *file, char __user *buf, size_t count,
10241024
char buffer[PROC_NUMBUF];
10251025
int oom_adj = OOM_ADJUST_MIN;
10261026
size_t len;
1027-
unsigned long flags;
10281027

10291028
if (!task)
10301029
return -ESRCH;
1031-
if (lock_task_sighand(task, &flags)) {
1032-
if (task->signal->oom_score_adj == OOM_SCORE_ADJ_MAX)
1033-
oom_adj = OOM_ADJUST_MAX;
1034-
else
1035-
oom_adj = (task->signal->oom_score_adj * -OOM_DISABLE) /
1036-
OOM_SCORE_ADJ_MAX;
1037-
unlock_task_sighand(task, &flags);
1038-
}
1030+
if (task->signal->oom_score_adj == OOM_SCORE_ADJ_MAX)
1031+
oom_adj = OOM_ADJUST_MAX;
1032+
else
1033+
oom_adj = (task->signal->oom_score_adj * -OOM_DISABLE) /
1034+
OOM_SCORE_ADJ_MAX;
10391035
put_task_struct(task);
10401036
len = snprintf(buffer, sizeof(buffer), "%d\n", oom_adj);
10411037
return simple_read_from_buffer(buf, count, ppos, buffer, len);
10421038
}
10431039

1040+
static DEFINE_MUTEX(oom_adj_mutex);
1041+
10441042
/*
10451043
* /proc/pid/oom_adj exists solely for backwards compatibility with previous
10461044
* 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,
10571055
struct task_struct *task;
10581056
char buffer[PROC_NUMBUF];
10591057
int oom_adj;
1060-
unsigned long flags;
10611058
int err;
10621059

10631060
memset(buffer, 0, sizeof(buffer));
@@ -1083,11 +1080,6 @@ static ssize_t oom_adj_write(struct file *file, const char __user *buf,
10831080
goto out;
10841081
}
10851082

1086-
if (!lock_task_sighand(task, &flags)) {
1087-
err = -ESRCH;
1088-
goto err_put_task;
1089-
}
1090-
10911083
/*
10921084
* Scale /proc/pid/oom_score_adj appropriately ensuring that a maximum
10931085
* value is always attainable.
@@ -1097,10 +1089,11 @@ static ssize_t oom_adj_write(struct file *file, const char __user *buf,
10971089
else
10981090
oom_adj = (oom_adj * OOM_SCORE_ADJ_MAX) / -OOM_DISABLE;
10991091

1092+
mutex_lock(&oom_adj_mutex);
11001093
if (oom_adj < task->signal->oom_score_adj &&
11011094
!capable(CAP_SYS_RESOURCE)) {
11021095
err = -EACCES;
1103-
goto err_sighand;
1096+
goto err_unlock;
11041097
}
11051098

11061099
/*
@@ -1113,9 +1106,8 @@ static ssize_t oom_adj_write(struct file *file, const char __user *buf,
11131106

11141107
task->signal->oom_score_adj = oom_adj;
11151108
trace_oom_score_adj_update(task);
1116-
err_sighand:
1117-
unlock_task_sighand(task, &flags);
1118-
err_put_task:
1109+
err_unlock:
1110+
mutex_unlock(&oom_adj_mutex);
11191111
put_task_struct(task);
11201112
out:
11211113
return err < 0 ? err : count;
@@ -1133,15 +1125,11 @@ static ssize_t oom_score_adj_read(struct file *file, char __user *buf,
11331125
struct task_struct *task = get_proc_task(file_inode(file));
11341126
char buffer[PROC_NUMBUF];
11351127
short oom_score_adj = OOM_SCORE_ADJ_MIN;
1136-
unsigned long flags;
11371128
size_t len;
11381129

11391130
if (!task)
11401131
return -ESRCH;
1141-
if (lock_task_sighand(task, &flags)) {
1142-
oom_score_adj = task->signal->oom_score_adj;
1143-
unlock_task_sighand(task, &flags);
1144-
}
1132+
oom_score_adj = task->signal->oom_score_adj;
11451133
put_task_struct(task);
11461134
len = snprintf(buffer, sizeof(buffer), "%hd\n", oom_score_adj);
11471135
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,
11521140
{
11531141
struct task_struct *task;
11541142
char buffer[PROC_NUMBUF];
1155-
unsigned long flags;
11561143
int oom_score_adj;
11571144
int err;
11581145

@@ -1179,25 +1166,21 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
11791166
goto out;
11801167
}
11811168

1182-
if (!lock_task_sighand(task, &flags)) {
1183-
err = -ESRCH;
1184-
goto err_put_task;
1185-
}
1186-
1169+
mutex_lock(&oom_adj_mutex);
11871170
if ((short)oom_score_adj < task->signal->oom_score_adj_min &&
11881171
!capable(CAP_SYS_RESOURCE)) {
11891172
err = -EACCES;
1190-
goto err_sighand;
1173+
goto err_unlock;
11911174
}
11921175

11931176
task->signal->oom_score_adj = (short)oom_score_adj;
11941177
if (has_capability_noaudit(current, CAP_SYS_RESOURCE))
11951178
task->signal->oom_score_adj_min = (short)oom_score_adj;
1179+
11961180
trace_oom_score_adj_update(task);
11971181

1198-
err_sighand:
1199-
unlock_task_sighand(task, &flags);
1200-
err_put_task:
1182+
err_unlock:
1183+
mutex_unlock(&oom_adj_mutex);
12011184
put_task_struct(task);
12021185
out:
12031186
return err < 0 ? err : count;

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