David, could you test with this patch please? --- >From c4a2a58d3856bc1e528f7c1622a59cef58033cb3 Mon Sep 17 00:00:00 2001 From: Michal Hocko <mho...@suse.com> Date: Thu, 7 Dec 2017 09:39:03 +0100 Subject: [PATCH] mm, oom_reaper: fix memory corruption
David Rientjes has reported the following memory corruption while the oom reaper tries to unmap the victims address space BUG: Bad page map in process oom_reaper pte:6353826300000000 pmd:00000000 addr:00007f50cab1d000 vm_flags:08100073 anon_vma:ffff9eea335603f0 mapping: (null) index:7f50cab1d file: (null) fault: (null) mmap: (null) readpage: (null) CPU: 2 PID: 1001 Comm: oom_reaper Call Trace: [<ffffffffa4bd967d>] dump_stack+0x4d/0x70 [<ffffffffa4a03558>] unmap_page_range+0x1068/0x1130 [<ffffffffa4a2e07f>] __oom_reap_task_mm+0xd5/0x16b [<ffffffffa4a2e226>] oom_reaper+0xff/0x14c [<ffffffffa48d6ad1>] kthread+0xc1/0xe0 Tetsuo Handa has noticed that the synchronization inside exit_mmap is insufficient. We only synchronize with the oom reaper if tsk_is_oom_victim which is not true if the final __mmput is called from a different context than the oom victim exit path. This can trivially happen from context of any task which has grabbed mm reference (e.g. to read /proc/<pid>/ file which requires mm etc.). The race would look like this oom_reaper oom_victim task mmget_not_zero do_exit mmput __oom_reap_task_mm mmput __mmput exit_mmap remove_vma unmap_page_range Fix this issue by providing a new mm_is_oom_victim() helper which operates on the mm struct rather than a task. Any context which operates on a remote mm struct should use this helper in place of tsk_is_oom_victim. The flag is set in mark_oom_victim and never cleared so it is stable in the exit_mmap path. Reported-by: David Rientjes <rient...@google.com> Debugged-by: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp> Fixes: 212925802454 ("mm: oom: let oom_reap_task and exit_mmap run concurrently") Cc: stable # 4.14 Signed-off-by: Michal Hocko <mho...@suse.com> --- include/linux/oom.h | 9 +++++++++ include/linux/sched/coredump.h | 5 +++-- mm/mmap.c | 2 +- mm/oom_kill.c | 4 +++- 4 files changed, 16 insertions(+), 4 deletions(-) diff --git a/include/linux/oom.h b/include/linux/oom.h index 27cd36b762b5..c4139e79771d 100644 --- a/include/linux/oom.h +++ b/include/linux/oom.h @@ -77,6 +77,15 @@ static inline bool tsk_is_oom_victim(struct task_struct * tsk) return tsk->signal->oom_mm; } +/* + * Use this helper if tsk->mm != mm and the victim mm needs a special + * handling. This is guaranteed to stay true after once set. + */ +static inline bool mm_is_oom_victim(struct mm_struct *mm) +{ + return test_bit(MMF_OOM_VICTIM, &mm->flags); +} + /* * Checks whether a page fault on the given mm is still reliable. * This is no longer true if the oom reaper started to reap the diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h index 9c8847395b5e..da673ca66e7a 100644 --- a/include/linux/sched/coredump.h +++ b/include/linux/sched/coredump.h @@ -68,8 +68,9 @@ static inline int get_dumpable(struct mm_struct *mm) #define MMF_RECALC_UPROBES 20 /* MMF_HAS_UPROBES can be wrong */ #define MMF_OOM_SKIP 21 /* mm is of no interest for the OOM killer */ #define MMF_UNSTABLE 22 /* mm is unstable for copy_from_user */ -#define MMF_HUGE_ZERO_PAGE 23 /* mm has ever used the global huge zero page */ -#define MMF_DISABLE_THP 24 /* disable THP for all VMAs */ +#define MMF_OOM_VICTIM 23 /* mm is the oom victim */ +#define MMF_HUGE_ZERO_PAGE 24 /* mm has ever used the global huge zero page */ +#define MMF_DISABLE_THP 25 /* disable THP for all VMAs */ #define MMF_DISABLE_THP_MASK (1 << MMF_DISABLE_THP) #define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\ diff --git a/mm/mmap.c b/mm/mmap.c index 476e810cf100..d00a06248ef1 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -3005,7 +3005,7 @@ void exit_mmap(struct mm_struct *mm) unmap_vmas(&tlb, vma, 0, -1); set_bit(MMF_OOM_SKIP, &mm->flags); - if (unlikely(tsk_is_oom_victim(current))) { + if (unlikely(mm_is_oom_victim(mm))) { /* * Wait for oom_reap_task() to stop working on this * mm. Because MMF_OOM_SKIP is already set before diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 3b0d0fed8480..e4d290b6804b 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -666,8 +666,10 @@ static void mark_oom_victim(struct task_struct *tsk) return; /* oom_mm is bound to the signal struct life time. */ - if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm)) + if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm)) { mmgrab(tsk->signal->oom_mm); + set_bit(MMF_OOM_VICTIM, &mm->flags); + } /* * Make sure that the task is woken up from uninterruptible sleep -- 2.15.0 -- Michal Hocko SUSE Labs