Messages in this thread Patch in this message | | | Date | Wed, 3 Dec 2014 13:58:10 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH v2 1/1] oom: don't assume that a coredumping thread will exit soon |
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On Wed, 3 Dec 2014 20:50:20 +0100 Oleg Nesterov <oleg@redhat.com> wrote:
> oom_kill.c assumes that PF_EXITING task should exit and free the memory > soon. This is wrong in many ways and one important case is the coredump. > A task can sleep in exit_mm() "forever" while the coredumping sub-thread > can need more memory. > > Change the PF_EXITING checks to take SIGNAL_GROUP_COREDUMP into account, > we add the new trivial helper for that. > > Note: this is only the first step, this patch doesn't try to solve other > problems. The SIGNAL_GROUP_COREDUMP check is obviously racy, a task can > participate in coredump after it was already observed in PF_EXITING state, > so TIF_MEMDIE (which also blocks oom-killer) still can be wrongly set. > fatal_signal_pending() can be true because of SIGNAL_GROUP_COREDUMP so > out_of_memory() and mem_cgroup_out_of_memory() shouldn't blindly trust it. > And even the name/usage of the new helper is confusing, an exiting thread > can only free its ->mm if it is the only/last task in thread group. > > ... > > --- a/include/linux/oom.h > +++ b/include/linux/oom.h > @@ -92,6 +92,12 @@ static inline bool oom_gfp_allowed(gfp_t gfp_mask) > > extern struct task_struct *find_lock_task_mm(struct task_struct *p); > > +static inline bool task_will_free_mem(struct task_struct *task) > +{ > + return (task->flags & PF_EXITING) && > + !(task->signal->flags & SIGNAL_GROUP_COREDUMP); > +}
The SIGNAL_GROUP_COREDUMP test is utterly obscure. Let's help our poor readers?
--- a/include/linux/oom.h~oom-dont-assume-that-a-coredumping-thread-will-exit-soon-v2-fix +++ a/include/linux/oom.h @@ -89,6 +89,11 @@ extern struct task_struct *find_lock_tas static inline bool task_will_free_mem(struct task_struct *task) { + /* + * A coredumping process may sleep for extended periods in exit_mm(), so + * the oom killer cannot assume that the process will promptly exit and + * release memory. + */ return (task->flags & PF_EXITING) && !(task->signal->flags & SIGNAL_GROUP_COREDUMP); }
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