[PATCH 3/5] oom: introduce find_lock_task_mm() to fix !mm false positives
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From: KOSAKI Motohiro on 31 May 2010 05:40 From: Oleg Nesterov <oleg(a)redhat.com> Subject: [PATCH 3/5] oom: introduce find_lock_task_mm() to fix !mm false positives Almost all ->mm == NUL checks in oom_kill.c are wrong. The current code assumes that the task without ->mm has already released its memory and ignores the process. However this is not necessarily true when this process is multithreaded, other live sub-threads can use this ->mm. - Remove the "if (!p->mm)" check in select_bad_process(), it is just wrong. - Add the new helper, find_lock_task_mm(), which finds the live thread which uses the memory and takes task_lock() to pin ->mm - change oom_badness() to use this helper instead of just checking ->mm != NULL. - As David pointed out, select_bad_process() must never choose the task without ->mm, but no matter what badness() returns the task can be chosen if nothing else has been found yet. Note! This patch is not enough, we need more changes. - badness() was fixed, but oom_kill_task() still ignores the task without ->mm This will be addressed later. Signed-off-by: Oleg Nesterov <oleg(a)redhat.com> Cc: David Rientjes <rientjes(a)google.com> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro(a)jp.fujitsu.com> [rebase latest -mm and remove some obsoleted description] --- mm/oom_kill.c | 28 +++++++++++++++++----------- 1 files changed, 17 insertions(+), 11 deletions(-) diff --git a/mm/oom_kill.c b/mm/oom_kill.c index c87a6f4..162af2e 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -52,6 +52,19 @@ static int has_intersects_mems_allowed(struct task_struct *tsk) return 0; } +static struct task_struct *find_lock_task_mm(struct task_struct *p) +{ + struct task_struct *t = p; + do { + task_lock(t); + if (likely(t->mm)) + return t; + task_unlock(t); + } while_each_thread(p, t); + + return NULL; +} + /** * badness - calculate a numeric value for how bad this task has been * @p: task struct of which task we should calculate @@ -74,7 +87,6 @@ static int has_intersects_mems_allowed(struct task_struct *tsk) unsigned long badness(struct task_struct *p, unsigned long uptime) { unsigned long points, cpu_time, run_time; - struct mm_struct *mm; struct task_struct *child; int oom_adj = p->signal->oom_adj; struct task_cputime task_time; @@ -84,17 +96,14 @@ unsigned long badness(struct task_struct *p, unsigned long uptime) if (oom_adj == OOM_DISABLE) return 0; - task_lock(p); - mm = p->mm; - if (!mm) { - task_unlock(p); + p = find_lock_task_mm(p); + if (!p) return 0; - } /* * The memory size of the process is the basis for the badness. */ - points = mm->total_vm; + points = p->mm->total_vm; /* * After this unlock we can no longer dereference local variable `mm' @@ -117,7 +126,7 @@ unsigned long badness(struct task_struct *p, unsigned long uptime) */ list_for_each_entry(child, &p->children, sibling) { task_lock(child); - if (child->mm != mm && child->mm) + if (child->mm != p->mm && child->mm) points += child->mm->total_vm/2 + 1; task_unlock(child); } @@ -256,9 +265,6 @@ static struct task_struct *select_bad_process(unsigned long *ppoints, for_each_process(p) { unsigned long points; - /* skip the tasks which have already released their mm. */ - if (!p->mm) - continue; /* skip the init task and kthreads */ if (is_global_init(p) || (p->flags & PF_KTHREAD)) continue; -- 1.6.5.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |