From: Michal Hocko <mhocko@xxxxxxxx> Subject: mm, oom_reaper: skip mm structs with mmu notifiers Andrea has noticed that the oom_reaper doesn't invalidate the range via mmu notifiers (mmu_notifier_invalidate_range_start, mmu_notifier_invalidate_range_end) and that can corrupt the memory of the kvm guest for example. tlb_flush_mmu_tlbonly already invokes mmu notifiers but that is not sufficient as per Andrea: : mmu_notifier_invalidate_range cannot be used in replacement of : mmu_notifier_invalidate_range_start/end. For KVM : mmu_notifier_invalidate_range is a noop and rightfully so. A MMU : notifier implementation has to implement either : ->invalidate_range method or the invalidate_range_start/end : methods, not both. And if you implement invalidate_range_start/end : like KVM is forced to do, calling mmu_notifier_invalidate_range in : common code is a noop for KVM. : : For those MMU notifiers that can get away only implementing : ->invalidate_range, the ->invalidate_range is implicitly called by : mmu_notifier_invalidate_range_end(). And only those secondary MMUs : that share the same pagetable with the primary MMU (like AMD : iommuv2) can get away only implementing ->invalidate_range. As the callback is allowed to sleep and the implementation is out of hand of the MM it is safer to simply bail out if there is an mmu notifier registered. In order to not fail too early make the mm_has_notifiers check under the oom_lock and have a little nap before failing to give the current oom victim some more time to exit. [akpm@xxxxxxxxxxxxxxxxxxxx: coding-style fixes] Link: http://lkml.kernel.org/r/20170913113427.2291-1-mhocko@xxxxxxxxxx Fixes: aac453635549 ("mm, oom: introduce oom reaper") Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> Reported-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> Reviewed-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/mmu_notifier.h | 5 +++++ mm/oom_kill.c | 16 ++++++++++++++++ 2 files changed, 21 insertions(+) diff -puN include/linux/mmu_notifier.h~mm-oom_reaper-skip-mm-structs-with-mmu-notifiers include/linux/mmu_notifier.h --- a/include/linux/mmu_notifier.h~mm-oom_reaper-skip-mm-structs-with-mmu-notifiers +++ a/include/linux/mmu_notifier.h @@ -400,6 +400,11 @@ extern void mmu_notifier_synchronize(voi #else /* CONFIG_MMU_NOTIFIER */ +static inline int mm_has_notifiers(struct mm_struct *mm) +{ + return 0; +} + static inline void mmu_notifier_release(struct mm_struct *mm) { } diff -puN mm/oom_kill.c~mm-oom_reaper-skip-mm-structs-with-mmu-notifiers mm/oom_kill.c --- a/mm/oom_kill.c~mm-oom_reaper-skip-mm-structs-with-mmu-notifiers +++ a/mm/oom_kill.c @@ -40,6 +40,7 @@ #include <linux/ratelimit.h> #include <linux/kthread.h> #include <linux/init.h> +#include <linux/mmu_notifier.h> #include <asm/tlb.h> #include "internal.h" @@ -494,6 +495,21 @@ static bool __oom_reap_task_mm(struct ta goto unlock_oom; } + /* + * If the mm has notifiers then we would need to invalidate them around + * unmap_page_range and that is risky because notifiers can sleep and + * what they do is basically undeterministic. So let's have a short + * sleep to give the oom victim some more time. + * TODO: we really want to get rid of this ugly hack and make sure that + * notifiers cannot block for unbounded amount of time and add + * mmu_notifier_invalidate_range_{start,end} around unmap_page_range + */ + if (mm_has_notifiers(mm)) { + up_read(&mm->mmap_sem); + schedule_timeout_idle(HZ); + goto unlock_oom; + } + /* * MMF_OOM_SKIP is set by exit_mmap when the OOM reaper can't * work on the mm anymore. The check for MMF_OOM_SKIP must run _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
