linux-kernel - Re: [akpm-mm:mm-unstable 284/293] mm/khugepaged.c:2409 madvise_collapse() warn: possible memory leak of 'cc'

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Date:   Wed, 13 Jul 2022 07:24:14 -0700
From:   Zach O'Keefe <zokeefe@...gle.com>
To:     Yang Shi <shy828301@...il.com>
Cc:     Dan Carpenter <dan.carpenter@...cle.com>, kbuild@...ts.01.org,
        kernel test robot <lkp@...el.com>, kbuild-all@...ts.01.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [akpm-mm:mm-unstable 284/293] mm/khugepaged.c:2409
 madvise_collapse() warn: possible memory leak of 'cc'

On Jul 12 10:02, Yang Shi wrote:
> On Tue, Jul 12, 2022 at 5:36 AM Dan Carpenter <dan.carpenter@...cle.com> wrote:
> >
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-unstable
> > head:   0e9f775fb0b4adf1a4ef50ea156ead09a0fc5194
> > commit: 9f626ffb1d1c5c26b4a8e0fdffec784a5f773274 [284/293] mm/madvise: introduce MADV_COLLAPSE sync hugepage collapse
> > config: i386-randconfig-m021 (https://download.01.org/0day-ci/archive/20220710/202207100715.TBIYQ4fc-lkp@intel.com/config)
> > compiler: gcc-11 (Debian 11.3.0-3) 11.3.0
> >
> > If you fix the issue, kindly add following tag where applicable
> > Reported-by: kernel test robot <lkp@...el.com>
> > Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> >
> > smatch warnings:
> > mm/khugepaged.c:2409 madvise_collapse() warn: possible memory leak of 'cc'
> >
> > vim +/cc +2409 mm/khugepaged.c
> >
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2387  int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev,
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2388                 unsigned long start, unsigned long end)
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2389  {
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2390    struct collapse_control *cc;
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2391    struct mm_struct *mm = vma->vm_mm;
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2392    unsigned long hstart, hend, addr;
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2393    int thps = 0, last_fail = SCAN_FAIL;
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2394    bool mmap_locked = true;
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2395
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2396    BUG_ON(vma->vm_start > start);
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2397    BUG_ON(vma->vm_end < end);
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2398
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2399    cc = kmalloc(sizeof(*cc), GFP_KERNEL);
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2400    if (!cc)
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2401            return -ENOMEM;
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2402    cc->is_khugepaged = false;
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2403    cc->last_target_node = NUMA_NO_NODE;
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2404
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2405    *prev = vma;
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2406
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2407    /* TODO: Support file/shmem */
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06  2408    if (!vma->anon_vma || !vma_is_anonymous(vma))
> > 9f626ffb1d1c5c Zach O'Keefe 2022-07-06 @2409            return -EINVAL;
> 
> It seems better to move the cc kmalloc after the anonymous vma check?
>

Agreed - something I only noticed when fixing this. I've cleaned up some
ordering here, now looks like:

---8<---
	BUG_ON(vma->vm_start > start);
	BUG_ON(vma->vm_end < end);

	*prev = vma;

        /* TODO: Support file/shmem */
        if (!vma->anon_vma || !vma_is_anonymous(vma))
                return -EINVAL;

	if (!hugepage_vma_check(vma, vma->vm_flags, false, false, false))
		return -EINVAL;

	cc = kmalloc(sizeof(*cc), GFP_KERNEL);
	if (!cc)
		return -ENOMEM;
	cc->is_khugepaged = false;
	cc->last_target_node = NUMA_NO_NODE;

	mmgrab(mm);
	lru_add_drain_all();

	hstart = (start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
	hend = end & HPAGE_PMD_MASK;

	for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) {
---8<---
out_nolock:
	mmap_assert_locked(mm);
	mmdrop(mm);
	kfree(cc);
---8<---

> >
> > kfree(cc);?
> >
> >
> > --
> > 0-DAY CI Kernel Test Service
> > https://01.org/lkp
> >
> >