>
> 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.
>
> V2: The original version of the patch did not correctly handle placeholder
> entries before the range to be deleted. The new check is more specific
> and only matches placeholders at the start of range.
>
> Fixes: feba16e25a57 ("add region_del() to delete a specific range of entries")
> Cc: [email protected] [4.3]
> Signed-off-by: Mike Kravetz <[email protected]>
> Reported-by: Dmitry Vyukov <[email protected]>
> ---
Acked-by: Hillf Danton <[email protected]>
> mm/hugetlb.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 1101ccd94..c895ab9 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);
> @@ -483,8 +485,16 @@ 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)
> + /*
> + * Skip regions before the range to be deleted. 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
> + * at the beginning of the range to be deleted.
> + */
> + if (rg->to <= f && (rg->to != rg->from || rg->to != f))
> continue;
> +
> if (rg->from >= t)
> break;
>
> --
> 2.4.3