Re: [PATCH] mm/hugetlb resv map memory leak for placeholder entries

[Mike Kravetz]

On 12/02/2015 01:26 AM, Dmitry Vyukov wrote:
> FWIW, I see this leak also with mlock, mmap, get_mempolicy and page
> faults. So it is not specific only to the new fancy mlock2.

I assume/hope the patch addresses leaks with those other calls as well?

-- 
Mike Kravetz

> 
> 
> 
> 
> On Wed, Dec 2, 2015 at 8:12 AM, Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx> wrote:
>>>
>>> Dmitry Vyukov reported the following memory leak
>>>
>>> unreferenced object 0xffff88002eaafd88 (size 32):
>>>   comm "a.out", pid 5063, jiffies 4295774645 (age 15.810s)
>>>   hex dump (first 32 bytes):
>>>     28 e9 4e 63 00 88 ff ff 28 e9 4e 63 00 88 ff ff  (.Nc....(.Nc....
>>>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>>>   backtrace:
>>>     [<     inline     >] kmalloc include/linux/slab.h:458
>>>     [<ffffffff815efa64>] region_chg+0x2d4/0x6b0 mm/hugetlb.c:398
>>>     [<ffffffff815f0c63>] __vma_reservation_common+0x2c3/0x390 mm/hugetlb.c:1791
>>>     [<     inline     >] vma_needs_reservation mm/hugetlb.c:1813
>>>     [<ffffffff815f658e>] alloc_huge_page+0x19e/0xc70 mm/hugetlb.c:1845
>>>     [<     inline     >] hugetlb_no_page mm/hugetlb.c:3543
>>>     [<ffffffff815fc561>] hugetlb_fault+0x7a1/0x1250 mm/hugetlb.c:3717
>>>     [<ffffffff815fd349>] follow_hugetlb_page+0x339/0xc70 mm/hugetlb.c:3880
>>>     [<ffffffff815a2bb2>] __get_user_pages+0x542/0xf30 mm/gup.c:497
>>>     [<ffffffff815a400e>] populate_vma_page_range+0xde/0x110 mm/gup.c:919
>>>     [<ffffffff815a4207>] __mm_populate+0x1c7/0x310 mm/gup.c:969
>>>     [<ffffffff815b74f1>] do_mlock+0x291/0x360 mm/mlock.c:637
>>>     [<     inline     >] SYSC_mlock2 mm/mlock.c:658
>>>     [<ffffffff815b7a4b>] SyS_mlock2+0x4b/0x70 mm/mlock.c:648
>>>
>>> Dmitry identified a potential memory leak in the routine region_chg,
>>> where a region descriptor is not free'ed on an error path.
>>>
>>> However, the root cause for the above memory leak resides in region_del.
>>> In this specific case, a "placeholder" entry is created in region_chg.  The
>>> associated page allocation fails, and the placeholder entry is left in the
>>> reserve map.  This is "by design" as the entry should be deleted when the
>>> map is released.  The bug is in the region_del routine which is used to
>>> delete entries within a specific range (and when the map is released).
>>> region_del did not handle the case where a placeholder entry exactly matched
>>> the start of the range range to be deleted.  In this case, the entry would
>>> not be deleted and leaked.  The fix is to take these special placeholder
>>> entries into account in region_del.
>>>
>>> The region_chg error path leak is also fixed.
>>>
>>> Fixes: feba16e25a57 ("add region_del() to delete a specific range of entries")
>>> Cc: stable@xxxxxxxxxxxxxxx [4.3]
>>> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
>>> Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
>>> ---
>>
>> Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
>>
>>>  mm/hugetlb.c | 12 ++++++++++--
>>>  1 file changed, 10 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>>> index 1101ccd94..ba07014 100644
>>> --- a/mm/hugetlb.c
>>> +++ b/mm/hugetlb.c
>>> @@ -372,8 +372,10 @@ retry_locked:
>>>               spin_unlock(&resv->lock);
>>>
>>>               trg = kmalloc(sizeof(*trg), GFP_KERNEL);
>>> -             if (!trg)
>>> +             if (!trg) {
>>> +                     kfree(nrg);
>>>                       return -ENOMEM;
>>> +             }
>>>
>>>               spin_lock(&resv->lock);
>>>               list_add(&trg->link, &resv->region_cache);
>>> @@ -483,7 +485,13 @@ static long region_del(struct resv_map *resv, long f, long t)
>>>  retry:
>>>       spin_lock(&resv->lock);
>>>       list_for_each_entry_safe(rg, trg, head, link) {
>>> -             if (rg->to <= f)
>>> +             /*
>>> +              * file_region ranges are normally of the form [from, to).
>>> +              * However, there may be a "placeholder" entry in the map
>>> +              * which is of the form (from, to) with from == to.  Check
>>> +              * for placeholder entries as well.
>>> +              */
>>> +             if (rg->to <= f && rg->to != rg->from)
>>>                       continue;
>>>               if (rg->from >= t)
>>>                       break;
>>> --
>>> 2.4.3
>>
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