mirrors/linux
1
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2026-04-03 09:56:50 -04:00
Code Issues Packages Projects Releases Wiki Activity

mm: hugetlb: fix incorrect fallback for subpool

Browse Source 
During our testing with hugetlb subpool enabled, we observe that
hstate->resv_huge_pages may underflow into negative values.  Root cause
analysis reveals a race condition in subpool reservation fallback handling
as follow:

hugetlb_reserve_pages()
    /* Attempt subpool reservation */
    gbl_reserve = hugepage_subpool_get_pages(spool, chg);

    /* Global reservation may fail after subpool allocation */
    if (hugetlb_acct_memory(h, gbl_reserve) < 0)
        goto out_put_pages;

out_put_pages:
    /* This incorrectly restores reservation to subpool */
    hugepage_subpool_put_pages(spool, chg);

When hugetlb_acct_memory() fails after subpool allocation, the current
implementation over-commits subpool reservations by returning the full
'chg' value instead of the actual allocated 'gbl_reserve' amount.  This
discrepancy propagates to global reservations during subsequent releases,
eventually causing resv_huge_pages underflow.

This problem can be trigger easily with the following steps:
1. reverse hugepage for hugeltb allocation
2. mount hugetlbfs with min_size to enable hugetlb subpool
3. alloc hugepages with two task(make sure the second will fail due to
   insufficient amount of hugepages)
4. with for a few seconds and repeat step 3 which will make
   hstate->resv_huge_pages to go below zero.

To fix this problem, return corrent amount of pages to subpool during the
fallback after hugepage_subpool_get_pages is called.

Link: https://lkml.kernel.org/r/20250410062633.3102457-1-mawupeng1@huawei.com
Fixes: 1c5ecae3a9 ("hugetlbfs: add minimum size accounting to subpools")
Signed-off-by: Wupeng Ma <mawupeng1@huawei.com>
Tested-by: Joshua Hahn <joshua.hahnjy@gmail.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: Ma Wupeng <mawupeng1@huawei.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Wupeng Ma
2025-04-10 14:26:33 +08:00
committed by Andrew Morton
parent 82f2b0b97b
commit a833a693a4
1 changed files with 22 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

28
mm/hugetlb.c
View File

@@ -3010,7 +3010,7 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
struct hugepage_subpool *spool = subpool_vma(vma);
struct hstate *h = hstate_vma(vma);
struct folio *folio;
long retval, gbl_chg;
long retval, gbl_chg, gbl_reserve;
map_chg_state map_chg;
int ret, idx;
struct hugetlb_cgroup *h_cg = NULL;
@@ -3163,8 +3163,16 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
hugetlb_cgroup_uncharge_cgroup_rsvd(idx, pages_per_huge_page(h),
h_cg);
out_subpool_put:
if (map_chg)
hugepage_subpool_put_pages(spool, 1);
/*
* put page to subpool iff the quota of subpool's rsv_hpages is used
* during hugepage_subpool_get_pages.
*/
if (map_chg && !gbl_chg) {
gbl_reserve = hugepage_subpool_put_pages(spool, 1);
hugetlb_acct_memory(h, -gbl_reserve);
}
out_end_reservation:
if (map_chg != MAP_CHG_ENFORCED)
vma_end_reservation(h, vma, addr);
@@ -7239,7 +7247,7 @@ bool hugetlb_reserve_pages(struct inode *inode,
struct vm_area_struct *vma,
vm_flags_t vm_flags)
{
long chg = -1, add = -1;
long chg = -1, add = -1, spool_resv, gbl_resv;
struct hstate *h = hstate_inode(inode);
struct hugepage_subpool *spool = subpool_inode(inode);
struct resv_map *resv_map;
@@ -7374,8 +7382,16 @@ bool hugetlb_reserve_pages(struct inode *inode,
return true;
out_put_pages:
/* put back original number of pages, chg */
(void)hugepage_subpool_put_pages(spool, chg);
spool_resv = chg - gbl_reserve;
if (spool_resv) {
/* put sub pool's reservation back, chg - gbl_reserve */
gbl_resv = hugepage_subpool_put_pages(spool, spool_resv);
/*
* subpool's reserved pages can not be put back due to race,
* return to hstate.
*/
hugetlb_acct_memory(h, -gbl_resv);
}
out_uncharge_cgroup:
hugetlb_cgroup_uncharge_cgroup_rsvd(hstate_index(h),
chg * pages_per_huge_page(h), h_cg);