On Tue, 6 Oct 2015, Michal Hocko wrote: > On Tue 06-10-15 18:28:04, Oleg Nesterov wrote: > > oom_kill_process() does atomic_inc(&mm->mm_users) to ensure that > > this ->mm can't go away and this is wrong, change it to rely on > > ->mm_count and mmdrop(). > > > > Firstly, we do not want to delay exit_mmap/etc if the victim exits > > before we do mmput(), but this is minor. > > > > More importantly, we simply can not do mmput() in oom_kill_process(), > > this can deadlock if (for example) the caller holds i_mmap_rwsem and > > mmput() actually leads to exit_mmap(); the victim can have this file > > mmaped and in this case unmap_vmas/free_pgtables paths will take the > > same lock for writing. And at least huge_pmd_share() does pmd_alloc() > > under i_mmap_rwsem because VM_HUGETLB memory is not reclaimable. > > Ouch, I have completely missed this during review! Thanks for catching > this. On the second thought it is clear now. We really want to pin the > mm_struct not the address space. > > > Signed-off-by: Oleg Nesterov <[email protected]> > > Acked-by: Michal Hocko <[email protected]>
Acked-by: Hugh Dickins <[email protected]> Thanks: looks like this is what was behind recent trinity/KSM deadlock, https://lkml.org/lkml/2015/10/1/563 > > > --- > > mm/oom_kill.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > > index 034d219..52abb78 100644 > > --- a/mm/oom_kill.c > > +++ b/mm/oom_kill.c > > @@ -571,7 +571,7 @@ void oom_kill_process(struct oom_control *oc, struct > > task_struct *p, > > > > /* Get a reference to safely compare mm after task_unlock(victim) */ > > mm = victim->mm; > > - atomic_inc(&mm->mm_users); > > + atomic_inc(&mm->mm_count); > > /* > > * We should send SIGKILL before setting TIF_MEMDIE in order to prevent > > * the OOM victim from depleting the memory reserves from the user > > @@ -609,7 +609,7 @@ void oom_kill_process(struct oom_control *oc, struct > > task_struct *p, > > } > > rcu_read_unlock(); > > > > - mmput(mm); > > + mmdrop(mm); > > put_task_struct(victim); > > } > > #undef K > > -- > > 2.4.3 > > > > -- > Michal Hocko > SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
