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From: Michal Hocko <mhocko@kernel.org>
To: <linux-mm@kvack.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
	David Rientjes <rientjes@google.com>,
	Oleg Nesterov <oleg@redhat.com>,
	Vladimir Davydov <vdavydov@parallels.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Michal Hocko <mhocko@suse.com>
Subject: [PATCH 01/10] proc, oom: drop bogus task_lock and mm check
Date: Fri,  3 Jun 2016 11:16:35 +0200	[thread overview]
Message-ID: <1464945404-30157-2-git-send-email-mhocko@kernel.org> (raw)
In-Reply-To: <1464945404-30157-1-git-send-email-mhocko@kernel.org>

From: Michal Hocko <mhocko@suse.com>

both oom_adj_write and oom_score_adj_write are using task_lock,
check for task->mm and fail if it is NULL. This is not needed because
the oom_score_adj is per signal struct so we do not need mm at all.
The code has been introduced by 3d5992d2ac7d ("oom: add per-mm oom
disable count") but we do not do per-mm oom disable since c9f01245b6a7
("oom: remove oom_disable_count").

The task->mm check is even not correct because the current thread might
have exited but the thread group might be still alive - e.g. thread
group leader would lead that echo $VAL > /proc/pid/oom_score_adj would
always fail with EINVAL while /proc/pid/task/$other_tid/oom_score_adj
would succeed. This is unexpected at best.

Remove the lock along with the check to fix the unexpected behavior
and also because there is not real need for the lock in the first place.

Reviewed-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 fs/proc/base.c | 22 ++++------------------
 1 file changed, 4 insertions(+), 18 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index be73f4d0cb01..a6014e45c516 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1083,15 +1083,9 @@ static ssize_t oom_adj_write(struct file *file, const char __user *buf,
 		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_lock;
+		goto err_put_task;
 	}
 
 	/*
@@ -1121,8 +1115,7 @@ static ssize_t oom_adj_write(struct file *file, const char __user *buf,
 	trace_oom_score_adj_update(task);
 err_sighand:
 	unlock_task_sighand(task, &flags);
-err_task_lock:
-	task_unlock(task);
+err_put_task:
 	put_task_struct(task);
 out:
 	return err < 0 ? err : count;
@@ -1186,15 +1179,9 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
 		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_lock;
+		goto err_put_task;
 	}
 
 	if ((short)oom_score_adj < task->signal->oom_score_adj_min &&
@@ -1210,8 +1197,7 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
 
 err_sighand:
 	unlock_task_sighand(task, &flags);
-err_task_lock:
-	task_unlock(task);
+err_put_task:
 	put_task_struct(task);
 out:
 	return err < 0 ? err : count;
-- 
2.8.1

  reply	other threads:[~2016-06-03  9:20 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-03  9:16 [PATCH 0/10 -v3] Handle oom bypass more gracefully Michal Hocko
2016-06-03  9:16 ` Michal Hocko [this message]
2016-06-03  9:16 ` [PATCH 02/10] proc, oom: drop bogus sighand lock Michal Hocko
2016-06-03  9:16 ` [PATCH 03/10] proc, oom_adj: extract oom_score_adj setting into a helper Michal Hocko
2016-06-03  9:16 ` [PATCH 04/10] mm, oom_adj: make sure processes sharing mm have same view of oom_score_adj Michal Hocko
2016-06-03  9:16 ` [PATCH 05/10] mm, oom: skip vforked tasks from being selected Michal Hocko
2016-06-03  9:16 ` [PATCH 06/10] mm, oom: kill all tasks sharing the mm Michal Hocko
2016-06-06 22:27   ` David Rientjes
2016-06-06 23:20     ` Oleg Nesterov
2016-06-07  6:37       ` Michal Hocko
2016-06-07 22:15       ` David Rientjes
2016-06-08  6:22         ` Michal Hocko
2016-06-08 22:51           ` David Rientjes
2016-06-09  6:46             ` Michal Hocko
2016-06-03  9:16 ` [PATCH 07/10] mm, oom: fortify task_will_free_mem Michal Hocko
2016-06-03  9:16 ` [PATCH 08/10] mm, oom: task_will_free_mem should skip oom_reaped tasks Michal Hocko
2016-06-03  9:16 ` [RFC PATCH 09/10] mm, oom_reaper: do not attempt to reap a task more than twice Michal Hocko
2016-06-03  9:16 ` [RFC PATCH 10/10] mm, oom: hide mm which is shared with kthread or global init Michal Hocko
2016-06-03 15:16   ` Tetsuo Handa
2016-06-06  8:15     ` Michal Hocko
2016-06-06 13:26     ` Michal Hocko
2016-06-07  6:26       ` Michal Hocko
2016-06-03 12:00 ` [PATCH 0/10 -v3] Handle oom bypass more gracefully Tetsuo Handa
2016-06-03 12:20   ` Michal Hocko
2016-06-03 12:22     ` Michal Hocko
2016-06-04 10:57       ` Tetsuo Handa
2016-06-06  8:39         ` Michal Hocko
2016-06-03 15:17     ` Tetsuo Handa
2016-06-06  8:36       ` Michal Hocko
2016-06-07 14:30         ` Tetsuo Handa
2016-06-07 15:05           ` Michal Hocko
2016-06-07 21:49             ` Tetsuo Handa
2016-06-08  7:27               ` Michal Hocko
2016-06-08 14:55                 ` Tetsuo Handa
2016-06-08 16:05                   ` Michal Hocko
2016-06-09 11:52 [PATCH 0/10 -v4] " Michal Hocko
2016-06-09 11:52 ` [PATCH 01/10] proc, oom: drop bogus task_lock and mm check Michal Hocko
2016-06-20 12:43 [PATCH 0/10 -v5] Handle oom bypass more gracefully Michal Hocko
2016-06-20 12:43 ` [PATCH 01/10] proc, oom: drop bogus task_lock and mm check Michal Hocko

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