From 3a5dda7a17cf3706f79b86293f29db02d61e0d48 Mon Sep 17 00:00:00 2001 From: David Rientjes Date: Tue, 22 Mar 2011 16:30:09 -0700 Subject: [PATCH] oom: prevent unnecessary oom kills or kernel panics This patch prevents unnecessary oom kills or kernel panics by reverting two commits: 495789a5 (oom: make oom_score to per-process value) cef1d352 (oom: multi threaded process coredump don't make deadlock) First, 495789a5 (oom: make oom_score to per-process value) ignores the fact that all threads in a thread group do not necessarily exit at the same time. It is imperative that select_bad_process() detect threads that are in the exit path, specifically those with PF_EXITING set, to prevent needlessly killing additional tasks. If a process is oom killed and the thread group leader exits, select_bad_process() cannot detect the other threads that are PF_EXITING by iterating over only processes. Thus, it currently chooses another task unnecessarily for oom kill or panics the machine when nothing else is eligible. By iterating over threads instead, it is possible to detect threads that are exiting and nominate them for oom kill so they get access to memory reserves. Second, cef1d352 (oom: multi threaded process coredump don't make deadlock) erroneously avoids making the oom killer a no-op when an eligible thread other than current isfound to be exiting. We want to detect this situation so that we may allow that exiting thread time to exit and free its memory; if it is able to exit on its own, that should free memory so current is no loner oom. If it is not able to exit on its own, the oom killer will nominate it for oom kill which, in this case, only means it will get access to memory reserves. Without this change, it is easy for the oom killer to unnecessarily target tasks when all threads of a victim don't exit before the thread group leader or, in the worst case, panic the machine. Signed-off-by: David Rientjes Cc: KOSAKI Motohiro Cc: KAMEZAWA Hiroyuki Cc: Oleg Nesterov Cc: Hugh Dickins Cc: Andrey Vagin Cc: [2.6.38.x] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/oom_kill.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 7dcca55ede7c..b5a7b5f46e7a 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -292,11 +292,11 @@ static struct task_struct *select_bad_process(unsigned int *ppoints, unsigned long totalpages, struct mem_cgroup *mem, const nodemask_t *nodemask) { - struct task_struct *p; + struct task_struct *g, *p; struct task_struct *chosen = NULL; *ppoints = 0; - for_each_process(p) { + do_each_thread(g, p) { unsigned int points; if (oom_unkillable_task(p, mem, nodemask)) @@ -324,7 +324,7 @@ static struct task_struct *select_bad_process(unsigned int *ppoints, * the process of exiting and releasing its resources. * Otherwise we could get an easy OOM deadlock. */ - if (thread_group_empty(p) && (p->flags & PF_EXITING) && p->mm) { + if ((p->flags & PF_EXITING) && p->mm) { if (p != current) return ERR_PTR(-1UL); @@ -337,7 +337,7 @@ static struct task_struct *select_bad_process(unsigned int *ppoints, chosen = p; *ppoints = points; } - } + } while_each_thread(g, p); return chosen; } -- 2.20.1