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.
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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