From: Andrew Morton Dave Peterson points out that badness() is playing with mm_structs without taking a reference on them. mmput() can sleep, so taking a reference here (inside tasklist_lock) is hard. Fix it up via task_lock() instead. Signed-off-by: Andrew Morton --- mm/oom_kill.c | 26 ++++++++++++++++++-------- 1 files changed, 18 insertions(+), 8 deletions(-) diff -puN mm/oom_kill.c~oom-kill-mm-locking-fix mm/oom_kill.c --- 25/mm/oom_kill.c~oom-kill-mm-locking-fix Fri Apr 14 14:31:29 2006 +++ 25-akpm/mm/oom_kill.c Fri Apr 14 14:31:29 2006 @@ -47,15 +47,25 @@ int sysctl_panic_on_oom; unsigned long badness(struct task_struct *p, unsigned long uptime) { unsigned long points, cpu_time, run_time, s; - struct list_head *tsk; + struct mm_struct *mm; + struct task_struct *child; - if (!p->mm) + task_lock(p); + mm = p->mm; + if (!mm) { + task_unlock(p); return 0; + } /* * The memory size of the process is the basis for the badness. */ - points = p->mm->total_vm; + points = mm->total_vm; + + /* + * After this unlock we can no longer dereference local variable `mm' + */ + task_unlock(p); /* * Processes which fork a lot of child processes are likely @@ -65,11 +75,11 @@ unsigned long badness(struct task_struct * child is eating the vast majority of memory, adding only half * to the parents will make the child our kill candidate of choice. */ - list_for_each(tsk, &p->children) { - struct task_struct *chld; - chld = list_entry(tsk, struct task_struct, sibling); - if (chld->mm != p->mm && chld->mm) - points += chld->mm->total_vm/2 + 1; + list_for_each_entry(child, &p->children, sibling) { + task_lock(child); + if (child->mm != mm && child->mm) + points += child->mm->total_vm/2 + 1; + task_unlock(child); } /* _